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BIOLOGY (1353 journals)            First | 3 4 5 6 7 8 9 10 | Last

International Journal of Acarology     Hybrid Journal   (Followers: 1)
International Journal of Applied Sciences and Biotechnology     Open Access   (Followers: 1)
International Journal of Aquatic Biology     Open Access   (Followers: 8)
International Journal of Basic, Applied and Innovative Research     Open Access  
International Journal of Bio-Inspired Computation     Hybrid Journal   (Followers: 1)
International Journal of Bioassays     Open Access   (Followers: 6)
International Journal of Biodiversity     Open Access   (Followers: 3)
International Journal of Biological and Chemical Sciences     Open Access   (Followers: 2)
International Journal of Biological Macromolecules     Hybrid Journal   (Followers: 1)
International Journal of Biological Sciences     Open Access   (Followers: 7)
International Journal of Biology     Open Access   (Followers: 3)
International Journal of Biomaterials     Open Access   (Followers: 4)
International Journal of Biomathematics     Hybrid Journal  
International Journal of Biomedical Engineering and Technology     Hybrid Journal   (Followers: 5)
International Journal of Biomedical Nanoscience and Nanotechnology     Hybrid Journal   (Followers: 7)
International Journal of Biometrics     Hybrid Journal   (Followers: 2)
International Journal of Brain Science     Full-text available via subscription  
International Journal of Cell Biology     Open Access   (Followers: 6)
International Journal of Chemical and Life Sciences     Open Access   (Followers: 3)
International Journal of Computational Biology and Drug Design     Hybrid Journal   (Followers: 1)
International Journal of Design Engineering     Hybrid Journal   (Followers: 12)
International Journal of Ecological Economics and Statistics     Full-text available via subscription   (Followers: 1)
International Journal of Ecology & Development     Full-text available via subscription   (Followers: 2)
International Journal of Ecosystem     Open Access   (Followers: 1)
International Journal of Engineering Science     Hybrid Journal   (Followers: 5)
International Journal of Enteric Pathogens     Open Access  
International Journal of Evolution     Partially Free   (Followers: 2)
International Journal of Evolutionary Biology     Open Access   (Followers: 11)
International Journal of Experimental and Computational Biomechanics     Hybrid Journal   (Followers: 4)
International Journal of Genomics     Open Access   (Followers: 2)
International Journal of High Throughput Screening     Open Access   (Followers: 2)
International Journal of Impact Engineering     Hybrid Journal   (Followers: 7)
International Journal of Innovation and Applied Studies     Open Access   (Followers: 2)
International Journal of Insect Science     Open Access   (Followers: 5)
International Journal of Knowledge Discovery in Bioinformatics     Full-text available via subscription   (Followers: 2)
International Journal of Life Science and Medical Research     Open Access   (Followers: 4)
International Journal of Life Sciences     Open Access   (Followers: 1)
International Journal of Medical Informatics     Hybrid Journal   (Followers: 10)
International Journal of Myriapodology     Open Access  
International Journal of Nanoparticles     Hybrid Journal   (Followers: 6)
International Journal of Natural Sciences     Open Access   (Followers: 1)
International Journal of Peptide Research and Therapeutics     Partially Free   (Followers: 5)
International Journal of Peptides     Open Access   (Followers: 5)
International Journal of Pharmaceutical and Life Sciences     Open Access   (Followers: 5)
International Journal of Phytoremediation     Hybrid Journal   (Followers: 2)
International Journal of Plant Genomics     Open Access   (Followers: 2)
International Journal of Plant Research     Open Access   (Followers: 1)
International Journal of Primatology     Hybrid Journal   (Followers: 3)
International Journal of Proteomics     Open Access   (Followers: 1)
International Journal of Signs and Semiotic Systems     Full-text available via subscription   (Followers: 1)
International Journal of Speleology     Open Access   (Followers: 10)
International Journal of Systems Biology and Biomedical Technologies     Full-text available via subscription   (Followers: 2)
International Journal of Tropical Insect Science     Hybrid Journal   (Followers: 1)
International Journal of Tryptophan Research     Open Access  
International Research Journal of Applied Life Sciences     Open Access  
International Review of Cell and Molecular Biology     Full-text available via subscription   (Followers: 5)
Intervirology     Full-text available via subscription  
IntraVital     Full-text available via subscription  
Invertebrate Biology     Hybrid Journal   (Followers: 6)
Invertebrate Neuroscience     Hybrid Journal   (Followers: 2)
Invertebrate Systematics     Hybrid Journal   (Followers: 5)
Iranian Journal of Parasitology     Open Access   (Followers: 2)
IRBM     Full-text available via subscription  
IRBM News     Full-text available via subscription  
Islets     Full-text available via subscription  
Israel Journal of Ecology and Evolution     Full-text available via subscription   (Followers: 2)
ISRN Bioinformatics     Open Access   (Followers: 2)
ISRN Biomarkers     Open Access  
ISRN Biomathematics     Open Access   (Followers: 1)
ISRN Computational Biology     Open Access   (Followers: 1)
ISRN Genomics     Open Access  
ITBM-RBM News     Full-text available via subscription   (Followers: 1)
IUBMB Life     Hybrid Journal   (Followers: 1)
IUFS Journal of Biology     Open Access  
Izvestiya Atmospheric and Oceanic Physics     Hybrid Journal   (Followers: 3)
Izvestiya, Physics of the Solid Earth     Hybrid Journal   (Followers: 4)
Japanese Journal of Applied Physics     Full-text available via subscription   (Followers: 4)
JCP : BioChemical Physics     Hybrid Journal  
JETP Letters     Hybrid Journal   (Followers: 3)
Journal of Bacteriology & Parasitology     Open Access   (Followers: 3)
Journal of Bioanalysis & Biomedicine     Open Access   (Followers: 1)
Journal of Bioequivalence & Bioavailability     Open Access  
Journal of Biometrics & Biostatistics     Open Access   (Followers: 1)
Journal of Bioremediation & Biodegradation     Open Access   (Followers: 2)
Journal of Biosensors & Bioelectronics     Open Access   (Followers: 2)
Journal of Bioterrorism & Biodefense     Open Access   (Followers: 1)
Journal of Cell Science & Therapy     Open Access   (Followers: 2)
Journal of Computer Science & Systems Biology     Open Access   (Followers: 2)
Journal of Proteomics & Bioinformatics     Open Access   (Followers: 6)
Journal of Advance Researches In Biological Sciences     Open Access   (Followers: 3)
Journal of Advances in Biology     Open Access   (Followers: 2)
Journal of Agricultural, Biological & Environmental Statistics     Hybrid Journal   (Followers: 7)
Journal of Amino Acids     Open Access   (Followers: 3)
Journal of Analytical & Bioanalytical Techniques     Open Access   (Followers: 5)
Journal of AOAC International     Full-text available via subscription   (Followers: 8)
Journal of Applied Biobehavioral Research     Hybrid Journal  
Journal of Applied Bioinformatics & Computational Biology     Partially Free   (Followers: 1)
Journal of Applied Biosciences     Open Access  
Journal of Applied Ichthyology     Hybrid Journal   (Followers: 6)
Journal of Applied Phycology     Hybrid Journal   (Followers: 9)

  First | 3 4 5 6 7 8 9 10 | Last

Journal Cover   Journal of Avian Biology
  [SJR: 1.066]   [H-I: 50]   [19 followers]  Follow
   Hybrid Journal Hybrid journal (It can contain Open Access articles)
   ISSN (Print) 0908-8857 - ISSN (Online) 1600-048X
   Published by John Wiley and Sons Homepage  [1606 journals]
  • Nest desertion cannot be considered an egg‐rejection mechanism in a
           medium‐sized host: an experimental study with the common blackbird
           Turdus merula
    • Authors: Manuel Soler; Francisco Ruiz‐Raya, Gianluca Roncalli, Juan Diego Ibáñez‐Álamo
      Abstract: Two main mechanisms of egg rejection, the main defence of hosts against brood parasites, have been described: ejection and desertion. Desertion of the parasitized nest is much more costly and is usually exhibited by small‐sized host species unable to remove the parasitic egg. However, nest desertion is frequently assumed to be an anti‐parasite strategy even in medium or large‐sized host species. This assumption should be considered with caution because: 1) large‐sized hosts able to eject the parasitic egg should eject it rather than desert the nest, and 2) breeding birds may desert their nests in response to different disturbances other than brood parasitism. This problem is especially important in the common blackbird Turdus merula because this is a medium‐sized species, potential host of the common cuckoo Cuculus canorus, in which desertion has been frequently reported as a response to cuckoo egg models. Here, we seek to determine whether nest desertion can be considered a response unequivocally directed to the parasitic egg in medium‐sized hosts using the blackbird as the study species. In an experimental study in which we have manipulated levels of mimicry and size of experimental eggs, we have found that both colour (mimetic and non‐mimetic; at least for human vision) and size (small, medium, and large) significantly affected ejection rates but not nest desertion rates. In fact, although large eggs disproportionally provoked nest desertion more frequently than did small or medium‐sized eggs, cuckoo‐sized parasitic eggs were not deserted allowing us to conclude that desertion is unlikely to be an adaptive response to brood parasitism at least for this species.
      PubDate: 2015-02-02T06:40:12.544161-05:
      DOI: 10.1111/jav.00571
  • Exploration and exploitation of foraging patches by desert sparrows:
           environmental indicators and local evaluation of spatially correlated
           costs and benefits
    • Authors: Fernando A. Milesi; Luis Marone
      Abstract: Conventional evolutionary and behavioral reasoning expects foragers to show strong spatial preferences in environments with heterogeneous resource distribution. Moreover, consumers should benefit from exploiting the information embedded in environmental features that indicate resource abundance. In desert soils seed abundance associates strong and reliably with vegetation and litter cover at small spatial scales. However, other spatially correlated factors (substrate complexity, temperature, predation risk) may affect foraging costs, benefits and decisions by ground‐feeding granivores. We used a sequence of three semi‐controlled field experiments of binary spatial choice within a portable aviary to identify the main cause of foraging microhabitat selection by the most abundant postdispersal granivorous bird in the central Monte desert (Argentina). In the first experiment we placed the aviary at field to offer pairs of adjacent microhabitats of unmodified, naturally‐contrasting substrates and environmental conditions to single, untrained rufous‐collared sparrows Zonotrichia capensis. Birds selected covered microhabitats in winter and summer, ruling out substrate complexity or thermoregulation as main single causes of patch selection. The other two experiments dissociated seed abundance, tree cover and litter to reveal their effects on patch selection. The results indicate that 1) sparrows do not restrict microhabitat exploration relying on environmental indicators, 2) distance to tree cover influences the order of patch exploration, probably in association with apprehension or risk‐assessment behavior, and 3) patch exploitation is determined by short‐term local estimation of seed abundance. The integration of these with previous results obtained under variable degrees of realism and experimental control allows for a better explanation of the spatial component of postdispersal granivory and its consequences on plants. The unconstrained selective foraging strategy of these sparrows would allow them to detect sporadic or ephemeral rich patches with structural characteristics indicating ‘low‐quality’, should promote the spatial homogenization of the palatable seed bank, and would favor indirect interactions between plants.
      PubDate: 2015-02-02T06:39:56.899313-05:
      DOI: 10.1111/jav.00388
  • Low‐budget ready‐to‐fly unmanned aerial vehicles: an
           effective tool for evaluating the nesting status of canopy‐breeding
           bird species
    • Authors: M. H. Weissensteiner; J. W. Poelstra, J. B. W. Wolf
      Abstract: Remotely controlled, unmanned aerial vehicles (UAVs) promise to be of high potential for a variety of applications in ecological and behavioural research. Off‐the‐shelf solutions have recently become available for civil use at steeply decreasing costs. In this study, we explored the utility of an UAV equipped with an on‐board camera (14 megapixel photo and 1920 × 1080 pixel video resolution) in assessing the breeding status, offspring number and age of a canopy‐breeding bird species, the hooded crow Corvus [corone] cornix. We further quantified performance and potential time savings using the UAV versus inspection with alternative approaches (optical instruments, camera on a telescopic rod, tree climbing). Nesting status, number and approximate age of nestlings could be assessed with good success in all 24 attempts using the UAV. Eighty‐five percent of the time required for inspection by climbing could be saved. Disturbance was moderate and lower than caused by climbing or using a camera on a telescopic rod. Additionally, UAV usage avoided tree damage and circumvented health risks associated with tree‐climbing.
      PubDate: 2015-01-23T08:51:19.183193-05:
      DOI: 10.1111/jav.00619
  • Plain wrens Cantorchilus modestus zeledoni adjust their singing tempo
           based on self and partner's cues to perform precisely coordinated duets
    • Authors: Karla D. Rivera‐Cáceres
      Abstract: Precise coordination appears to be an important signal in several duetting species. However, little attention has been directed to the proximate mechanisms that might drive this behavior. To perform highly coordinated duets, individuals can either have an intrinsic fixed singing tempo or modify their singing tempo based on cues in their own and their partner's songs. In this study I determined whether autogenous and/or heterogenous factors are associated with duet coordination in plain wrens Cantorchilus modestus zeledoni by analyzing recorded duets from 8 territorial pairs in the field. Previous research has determined that plain wrens perform highly coordinated antiphonal duets with almost no overlap. I found that to achieve such precise coordination individuals perform phrase‐by‐phrase modifications to the duration between two consecutive phrases (inter‐phrase interval) based on a) whether their song is answered, b) the phrase type used in the duet and c) the position of the inter‐phrase interval within the duet. Moreover, there are several sex differences in how individuals use these cues to modify their inter‐phrase intervals. Females produce longer inter‐phrase intervals when their mates do not answer a phrase, whereas males produce shorter inter‐phrase intervals when their mates do not answer. Females modify their inter‐phrase intervals based only on the phrase type their mates sing, whereas males modify their inter‐phrase intervals based on both the phrase that they sing and the phrase the females use to answer. Both males and females produce longer inter‐phrase intervals for longer phrase types sung by their partners, but males do so with more precision than do females. Finally both sexes increase their inter‐phrase intervals as the duet progresses. That precise coordination is achieved by a complex and dynamic process supports the idea that this behavior could signal pair bond strength.
      PubDate: 2015-01-23T08:51:04.333372-05:
      DOI: 10.1111/jav.00575
  • Malaria infection status predicts extra‐pair paternity in the blue
    • Authors: Edyta Podmokła; Anna Dubiec, Aneta Arct, Szymon M. Drobniak, Lars Gustafsson, Mariusz Cichoń
      Abstract: Extra‐pair matings comprise a common reproductive strategy among socially monogamous bird species. However, it remains unclear why females decide to mate with extra‐pair males. Indirect benefits in terms of improving offspring genetic quality are usually invoked to explain this phenomenon. Parasite resistance genes are often considered as a female target of seeking extra‐pair matings, but the direct test of this hypothesis is generally lacking. Here, we report on a relationship between the status of infection with malaria parasites (Plasmodium and Haemoproteus) and occurrence of extra‐pair paternity in a wild population of the blue tit Cyanistes caeruleus inhabiting Gotland (Sweden). We found that the probability of extra‐pair paternity is significantly related to the infection status of social parents. Infected males showed higher probability of being cuckolded than uninfected ones. However, this was observed only among males mated to uninfected females. Thus, avian malaria may potentially contribute to explanation of extra‐pair mating behaviour.
      PubDate: 2015-01-23T03:44:58.634191-05:
      DOI: 10.1111/jav.00599
  • Avian compass systems: do all migratory species possess all three'
    • Authors: Nikita Chernetsov
      PubDate: 2015-01-23T03:44:05.280492-05:
      DOI: 10.1111/jav.00593
  • Evolution of island warblers: beyond bills and masses
    • Authors: Bernd Leisler; Hans Winkler
      Abstract: In this paper, we take a closer look into the evolution of Acrocephalus warblers on islands in the Atlantic, Indian and Pacific Oceans. The shape‐related morphological evolution of island species is characterized by changes in the hind limb, flight, and feeding apparatus. Birds on islands converged to a morphology with strong legs, shorter rictal bristles, and rounder, more slotted and broader wings. Because of their high variance among islands, body size and bill dimensions did not contribute to the separation of continental and island forms, although bills tend to be longer on islands. The wings of island birds hardly vary among islands, unsurprisingly due to a lack of the adaptive features associated with long distance flights. The tendency towards shorter rictal bristles in the island warblers can be explained by the diminished role of aerial feeding, and closer contact with various substrates in the course of extractive foraging. The shift towards stronger legs in several insular species is remarkable because reed warblers on continents have even stronger legs than other passerines of comparable size. This trait correlates with diverse, acrobatic feeding techniques that are typically associated with broad habitat use. Bills reach extreme lengths on some islands. However, short bills occur as frequently, rendering this character highly variable among islands. Short bills indicate gleaning feeding techniques, whereas long bills are typical for species that pursue hidden and difficult‐to‐access prey. Body sizes differ greatly from island to island. On average, the sizes of island birds do not differ from continental ones, however. We suggest that vegetation clutter is the major driving force for this variation. The main conclusion following from our results is that evolution on islands pertains to all functional complexes, and not only the hitherto studied body size and bill dimensions.
      PubDate: 2015-01-20T06:25:37.981622-05:
      DOI: 10.1111/jav.00509
  • Are European birds leaving traditional wintering grounds in the
    • Authors: José Luis Tellería; Álvaro Ramírez, José Ignacio Aguirre
      Abstract: Climate warming and other environmental changes seem to be causing a shift in the wintering grounds of European birds northwards. We tested this hypothesis by exploring whether the abundance of 14 common migratory passerines (Passeriformes) wintering in Spain has decreased during recent decades. We used data on ringed birds provided by the European Union for Bird Ringing (EURING) with a capture per unit of effort approach to detect whether the number of foreign ring recoveries controlled by the total number of ringed birds has decreased during the last 60 yr. We also explored if trends of breeding populations, diet and body mass explained the observed patterns. Results show that the arrival of extra Iberian wintering birds has decreased since the 1980s. This tendency was weakly associated with the trends of breeding populations reported by the European Bird Census Council (EBCC). However, diet produced some suggestive patterns since frugivorous birds, a group adapted to tracking spatiotemporal changes in food availability, depicted sharper reductions in the number of wintering individuals. In addition, larger birds, less affected by winter thermoregulatory requirements, lessened their migratory movements to the south more than small birds. The results suggest a long‐term rearrangement of migratory movements of European birds in which the Mediterranean basin is losing its traditional role as primary wintering ground.
      PubDate: 2015-01-20T06:24:09.453841-05:
      DOI: 10.1111/jav.00588
  • Conspicuous calling near cryptic nests: a review of hypotheses and a field
           study on white‐browed scrubwrens
    • Authors: T. M. Haff; A. G. Horn, M. L. Leonard, R. D. Magrath
      Abstract: Predation is an important source of nest mortality in many bird species and calling near the nest can increase this risk, yet adults of many species regularly vocalize near their nests. Some of these calls serve clearly adaptive functions, such as alarm or provisioning calls. However, many species also give conspicuous ‘contact’ calls near the nest, which is puzzling because the function of these calls is unclear, and they might attract predators. Most studies of parental vocalizations near nests have focused on specific vocalizations and single hypotheses, yet there is a diversity of vocalization types and potential functions. We review the literature on the diversity and possible function of parental vocalizations near the nest, and then investigate the puzzle of conspicuous contact calling near nests by white‐browed scrubwrens Sericornis frontalis. In scrubwrens, ‘chip‐zz’ contact calls were almost always used when adults approached nests, and when they approached one another or changed location. Call composition also changed: the proportion of ‘chip’ elements increased as callers approached the nest or other adults. Neither adult sex nor nestling age affected calling. Thus, chip‐zz calls appear to be used as ongoing signals to other group members of the caller's activity and location, particularly relative to the nest. Nestlings appeared to use the calls as cues of adult arrival, and increased calling as adults approached nests. Further, adults called less after a predator was on the territory, suggesting that parents may be able to reduce the risk of chip‐zz calls betraying nest location, or possibly use the absence of calling as a signal of danger. This study thus demonstrates that calling near nests could inform both adults and nestlings about the caller's behaviour, and could serve multiple functions. Future studies will need to experimentally test these functions, as well as the other hypotheses reviewed here.
      PubDate: 2014-12-22T06:47:44.821645-05:
      DOI: 10.1111/jav.00622
  • Increased syllable rate during aggressive singing in a bird with complex
           and fast song
    • Authors: Caterina Funghi; Gonçalo C. Cardoso, Paulo G. Mota
      Abstract: Sexual signals can comprise traits with multiple functions, and species with extreme phenotypes offer an opportunity to link function with signal evolution. This is the case in the serin Serinus serinus, a songbird with extremely fast syllable rate compared to related finches, and high sound frequency for its body size. Previous work on receiver responses showed that playback of artificially increased syllable rate is avoided and inhibits vocal responses, suggesting it is perceived as aggressive, while, on the contrary, higher sound frequency appears preferred by females. We tested whether senders also change these traits during aggressive singing, with a field playback experiment. Serin males responding aggressively by approaching the playback loudspeaker also increased syllable rate, while males responding less aggressively did not change syllable rate. Together with work on receiver responses, this suggests that aggressive signalling may have been an important selective pressure for the evolution of extremely fast syllable rate in this species. It is noteworthy that aggressive male serins still increase syllable rate, despite of their already elevated natural syllable rate. We found no changes in sound frequency when singing aggressively, which agrees with previous work that instead showed a female preference for high song frequency. We conclude that the evolution of extreme traits in serin song is best explained by multiple functions.
      PubDate: 2014-12-22T06:47:31.254708-05:
      DOI: 10.1111/jav.00480
  • Incorporating site and year‐specific deuterium ratios (δ2H)
           from precipitation into geographic assignments of a migratory bird
    • Authors: Christopher M. Tonra; Christiaan Both, Peter P. Marra
      Pages: n/a - n/a
      Abstract: The study of migratory connectivity is rapidly growing in ornithology, as is the technology used to measure it. While use of extrinsic markers, such as archival tags, is becoming more prevalent, for many small species the best tool available for tracking birds remains intrinsic markers, such as stable‐hydrogen isotope ratios (δ2H). Many researchers have raised concerns that spatial and temporal environmental variation introduces a large amount of error into isotope‐based assignments, limiting their utility. Here, using feathers, we sought to address these issues in developing δ2H base maps for assigning pied flycatchers Ficedula hypoleuca of known origin to 15 sites across the breeding range (approx. 4 020 800 km2). We evaluated the effects of including random site variation and year‐specific precipitation δ2H (δ2HP) maps on assignments, compared to using mean annual growing season δ2Hp and no site effects. We found a positive correlation between feather δ2H (δ2HF) and mean annual δ2HP, resulting from large scale geographic variation. Repeatability of feather δ2H for individuals sampled in multiple years was strong overall, but variable among populations. Annual variation in δ2HP explained 21% of within individual variation in δ2HF. Neither year‐ nor site‐specific methods improved assignment precision or accuracy. All three methods assigned flycatchers of unknown origin captured at an African overwintering site to similar breeding areas. However, methods using long‐term means of δ2Hp assigned birds more precisely than year‐specific methods. Our results suggest that annual variation in this system is primarily a result of food web or individual level processes and that random site effects are not strong enough to drastically impact accuracy. We conclude that improvements in isotope based geographic assignments will rely on the addition of prior information, such as relative abundance in a Bayesian framework, or additional intrinsic markers.
      PubDate: 2014-12-12T03:38:40.187105-05:
      DOI: 10.1111/jav.00553
  • Egg removal by cuckoos forces hosts to accept parasite eggs
    • Authors: Osamu K. Mikami; Nozomu J. Sato, Keisuke Ueda, Keita D. Tanaka
      Pages: n/a - n/a
      Abstract: Many avian brood parasites remove one or more host eggs before laying their own eggs in the host nest. Various hypotheses have been proposed to explain the adaptive significance of this behaviour, but none of them provides an adequate explanation. Here we provide a new hypothesis for explaining why a parasite removes host eggs before laying its own. In this study, we attempted to answer this question by constructing a mathematical model that focused on the changes in host decision making according to reduced clutch size as a consequence of egg removal by parasites. We assume that a host selects one of the following two options to maximise the number of its own chicks: trying to eject a suspicious egg from the nest (trying‐to‐eject) or acceptance without trying to eject the egg (acceptance). The option selected depends on the number of eggs in the nest. Our model provides a new explanation for egg removal behaviour by showing that the host should select trying‐to‐eject if there is a large number of eggs in the nest but acceptance with a small number of eggs. This is because the relative payoff for a host that selects trying‐to‐eject decreases with the number of eggs in the nest. Therefore, parasites benefit by removing the host egg because this behaviour reduces the number of eggs in the nest, thereby increasing the probability of their own eggs being accepted. Thus, hosts have evolved egg ejection to combat brood parasites, but it may also have facilitated the evolution of egg removal by parasites. This hypothesis may also apply to brood parasitic species that do not eject host chicks. In addition, this hypothesis may explain other parasitic behaviours, such as egg damaging and egg puncturing, which lead to reductions in the host clutch size.
      PubDate: 2014-12-12T03:38:25.292508-05:
      DOI: 10.1111/jav.00410
  • The effects of spatial and temporal ecological variation on fatty acid
           compositions of wild great tits Parus major
    • Authors: Caroline Isaksson; Mark A. Hanson, Graham C. Burdge
      Pages: n/a - n/a
      Abstract: In birds, fatty acids (FA) have three main functions; they are structural components of cell membranes, metabolic fuel, and inflammatory molecules. Environmental factors, such as diet and ambient temperature, affect FA composition, thereby function and ultimately fitness. Thus, variation in FA compositions can be the underlying mechanism for varying performance of birds in different habitats. Here we examine variation in plasma FA composition in nestling and adult great tits Parus major, between 1) deciduous and coniferous, and 2) sun‐exposed and shaded habitats. The main results revealed that nestlings had a higher proportion of α‐linolenic acid (α‐LNA) in deciduous habitats and arachidonic acid in coniferous habitats. This reflects a difference in caterpillar availability between habitats with the deciduous habitat being caterpillar‐rich, whereas the coniferous habitats are rich in spiders. In addition, α‐LNA increased with nestling body condition in the coniferous habitat, supporting the importance of caterpillars for fledging success in this species. In line with dietary intake, the proportion of the essential α‐LNA and linoleic acid (LA) increased over the course of the day for all birds. In the deciduous habitat, adult females showed a positive association between LA and body condition. Furthermore, habitat sun‐exposure showed significant interactions with body condition for polyunsaturated FAs in nestlings, and with saturated FA in adult males, which is in accordance with the homeoviscous hypothesis stating that the proportion of saturated FA should decrease with decreasing ambient temperature. Taken together, small‐scale heterogeneity in habitat structure significantly influences FA compositions of great tits. Many of the results can be linked to dietary, and possibly, ambient temperature differences between habitats. These habitat effects on FA compositions can lead to different capacities of individual birds to deal with infections and low temperatures, two stressors that cause major mortality among wild birds.
      PubDate: 2014-12-12T03:38:12.374864-05:
      DOI: 10.1111/jav.00409
  • Timing of migration and residence areas during the non‐breeding
    • Authors: Felix Liechti; Chiara Scandolara, Diego Rubolini, Roberto Ambrosini, Fränzi Korner‐Nievergelt, Steffen Hahn, Roberto Lardelli, Maria Romano, Manuela Caprioli, Andrea Romano, Beatrice Sicurella, Nicola Saino
      Abstract: We investigated sex‐ and year‐dependent variation in the temporal and spatial movement pattern of barn swallows Hirundo rustica during the non‐breeding period. Hundred and three individuals equipped with miniaturized light‐level geolocators at three different breeding areas in southern Switzerland and northern Italy provided data for the analysis. We identified a region 1000 km in radius centred in Cameroon as the main non‐breeding residence area of these three geographical populations. Five residence areas of males only were in southern Africa, south of 19°S. Most individuals occupied a single site during their stay south of the Sahara. The timing of migration broadly overlapped between sexes and all geographical breeding populations. Between the two study years there was a distinct difference of 5 to 10 d in departure dates from and arrival at the breeding sites. Remarkably, the period of residence in sub‐Saharan Africa was very similar (157 d) in the two study years, but their positions in the first year (2010–2011) were about 400 km more to the north than in the second (2011–2012). Independent of the year, individuals with sub‐Saharan residence areas further north and east had a shorter pre‐breeding migration and arrived earlier than those staying further south and west. In addition, birds breeding in southern Switzerland arrived at their breeding colony 7–10 d later than those breeding only 100 km south, in the Po river plain. Our study provides new information on the variance in migration phenology and the distribution of residence areas in sub‐Saharan Africa in relation to sex, population and year. It supports the usefulness of light‐level geolocators for the study of annual routines of large samples of small birds.
      PubDate: 2014-12-01T03:16:42.856868-05:
      DOI: 10.1111/jav.00485
  • Wide ranging stopover movements and substantial fuelling in first year
           garden warblers at a northern stopover site
    • Authors: Robert Stach; Thord Fransson, Sven Jakobsson, Cecilia Kullberg
      Abstract: Migratory birds use stopovers to replenish their fuel reserves and they generally spend more time at stopover sites than they do in actual flight. When arriving at a new stopover site birds may need to search extensively to find a suitable feeding area and this search and settling period may affect the duration of stopover. Stopover behaviour can thus have profound effects on the migratory programme and studies on stopover behaviour are important to understand migratory strategies. We followed 51 first‐year garden warblers Sylvia borin with radio‐transmitters at an autumn stopover site on the island of Gotland in southern Sweden. Our aim was to determine the distance birds relocated from the coastal capture site when searching for an area to settle in, and also to establish the duration of stopover and put it in relation to refuelling rate by recapturing a subset of the radio‐tracked individuals. Sixteen birds made an extended stopover (> 2 d), relocated inland from the capture site and settled on average 5.6 km from the capture site, with the longest recorded relocation being fourteen kilometres. Birds that relocated nocturnally settled in areas further away than birds that relocated diurnally. Thirteen birds that continued migration after a short stop carried larger fuel stores than birds that stopped over longer and they remained close to the capture site until departure. Three birds were re‐trapped and showed high fuelling rates, between 0.3 and 1.1 g d–1. They left the stopover site with fuel loads between 40–56 percent of lean body mass, which possibly would have allowed them to reach the Mediterranean area without additional refuelling stops.
      PubDate: 2014-11-27T03:08:28.059439-05:
      DOI: 10.1111/jav.00492
  • Testing assumptions of central place foraging theory: a study of
           Adélie penguins Pygoscelis adeliae in the Ross Sea
    • Authors: R. Glenn Ford; David G. Ainley, Amelie Lescroël, Phil O'B. Lyver, Viola Toniolo, Grant Ballard
      Abstract: We investigated central place foraging (CPF) in the context of optimal foraging theory in Adélie penguins Pygoscelis adeliae of the southern Ross Sea by using satellite tracking and time‐depth recorders to explore foraging at two spatio‐temporal scales: within the day‐to‐day (sub‐mesoscale: single foraging trip, 10s of km2) and the entire breeding season (mesoscale: trips by multiple individuals across the collective foraging area, 100s of km2). Specifically, we examine whether three basic assumptions of the Orians–Pearson CPF model, shown to occur in other CPF species, are met: 1) within a patch, the rate of prey acquisition declines with time spent in that patch; 2) food is distributed in discrete patches and is not available between those patches; and 3) CPF species have knowledge of the potential (or average, at least) feeding rate within their universe of patches, and use this knowledge to determine their foraging strategy when planning or engaging in a foraging trip. We found that prey consumption rates did not decline with time spent in patches, and penguins foraged to some degree most of the time when at sea. Food availability, as measured by foraging dive rate, appeared to be predictable within the same day at the same location, but predictability broke down after 2 d at distances > 10 km away. We conclude that the assumptions of the Orians–Pearson CPF model are not a good fit to the circumstances of Ross Sea penguins, which clearly are central place foragers.
      PubDate: 2014-11-27T03:07:36.871499-05:
      DOI: 10.1111/jav.00491
  • Hawk mimicry in cuckoos and anti‐parasitic aggressive behavior of
           barn swallows in Denmark and China
    • Authors: Wei Liang; Anders Pape Møller
      Abstract: Hosts of brood parasites defend their nests against parasitism by aggression and subsequently, if parasitized, by rejection of the parasite egg or nestling. Cuckoos have evolved plumage mimicry with convergence towards the phenotype of Accipiter hawks that are common predators of cuckoo hosts. Here we tested two alternative hypotheses 1) whether barn swallows Hirundo rustica have evolved less aggressive behavior towards cuckoos in areas of sympatry with more abundant Accipiter hawks; and 2) whether barn swallows have evolved more aggressive anti‐parasite behavior in areas with a single species of cuckoo. We presented dummies of common cuckoo Cuculus canorus, sparrowhawk Accipiter nisus and Oriental turtledove Streptopelia orientalis (a benign control) at the nests of barn swallows during breeding, while recording intensity of response and proximity of barn swallows to the dummy. We demonstrated that cuckoos moved away when attacked aggressively and approached more closely by barn swallows showing that barn swallow behavior was efficient at driving away cuckoos. Barn swallows were significantly more aggressive and approached cuckoo and sparrowhawk dummies more closely in Denmark than in China, despite sparrowhawks being relatively more common in Denmark. Responses towards cuckoo dummies differed from responses towards sparrowhawk dummies, showing that barn swallows distinguished between the two different causes of danger. These findings are inconsistent with a less aggressive response towards cuckoo dummies in areas of sympatry with more abundant Accipiter hawks, but consistent with the alternative hypothesis that barn swallows have evolved more aggressive behavior towards cuckoos in areas with a single species of brood parasite, but not in areas with multiple species of parasites, where it is harder for hosts to tell the difference.
      PubDate: 2014-11-06T09:13:00.676307-05:
      DOI: 10.1111/jav.00515
  • Pair bond characteristics and maintenance in free‐flying jackdaws
           Corvus monedula: effects of social context and season
    • Authors: Robin J. Kubitza; Thomas Bugnyar, Christine Schwab
      Abstract: Most birds rely on cooperation between pair partners for breeding. In long‐term monogamous species, pair bonds are considered the basic units of social organization, albeit these birds often form foraging, roosting or breeding groups in which they repeatedly interact with numerous conspecifics. Focusing on jackdaws Corvus monedula, we here investigated 1) the interplay between pair bond and group dynamics in several social contexts and 2) how pair partners differ in individual effort of pair bond maintenance. Based on long‐term data on free‐flying birds, we quantified social interactions between group members within three positive contexts (spatial proximity, feeding and sociopositive interactions) for different periods of the year (non‐breeding, pre‐breeding, parental care). On the group level, we found that the number of interaction partners was highest in the spatial proximity context while in the feeding and sociopositive contexts the number of interaction partners was low and moderately low, respectively. Interactions were reciprocated within almost all contexts and periods. Investigating subgrouping within the flock, results showed that interactions were preferentially directed towards the respective pair partner compared to unmated adults. When determining pair partner effort, both sexes similarly invested most into mutual proximity during late winter, thereby refreshing their bond before the onset of breeding. Paired males fed their mates over the entire year at similar rates while paired females hardly fed their mates at all but engaged in sociopositive behaviors instead. We conclude that jackdaws actively seek out positive social ties to flock members (close proximity, sociopositive behavior), at certain times of the year. Thus, the group functions as a dynamic social unit, nested within are highly cooperative pair bonds. Both sexes invested into the bond with different social behaviors and different levels of effort, yet these are likely male and female proximate mechanisms aimed at maintaining and perpetuating the pair bond.
      PubDate: 2014-11-06T09:12:44.769876-05:
      DOI: 10.1111/jav.00508
  • Breeding performance and survival in the peregrine falcon Falco peregrinus
           support an age‐related competence improvement hypothesis mediated
           via an age threshold
    • Authors: Jabi Zabala; Iñigo Zuberogoitia
      Abstract: We studied the effects of age on breeding performance and survival probability in a peregrine falcon population, using data from a long term monitoring programme (carried out over 16 yr), in which we were able to identify individual birds. We compared the breeding performance and survival of yearling breeders, first‐time adult breeders and adult breeders. We found significant differences in breeding performance but not in survival. Yearling breeders had lower breeding success than older individuals but the breeding performance of inexperienced adults did not differ from that of experienced adults. We did not find changes in terminal breeding success since peregrines in their last year of life sustained the performance levels shown in previous years although with increasing variability. We found no evidence that attempting to breed affected survival probability in any age group. We argue that differences in breeding performance are related to age, not to breeding experience, and that there is an age threshold, coincident with the development of adult plumage, after which breeding performance is not affected either by age or experience. Peregrines that start breeding as yearlings are likely to have greater lifetime reproductive success than birds entering the breeding pool as adults. Consequently, such birds may represent a set of high quality individuals. Our results support the age‐related competence improvement hypothesis as being the relevant explanation for the increase in breeding performance with age.
      PubDate: 2014-11-06T09:12:32.782623-05:
      DOI: 10.1111/jav.00505
  • Ratios, adaptations, and the differential metabolic capability of avian
           flight muscles
    • Authors: Joseph R. Jehl; Annette E. Henry, David L. Swanson
      Abstract: The eared grebe Podiceps nigricollis shows seasonal variation in the relative size of the major flight muscles that lift and lower the wing: respectively, supracoracoideus (s) and pectoralis (p). S/p ratios are low (≈0.07–0.12) when grebes are in flying condition, higher (≈0.11–0.15) when staging and flightless, and extreme (to 0.29) when starving. Shifts were driven by changes in the protein content in the pectoralis; intramuscular fat had little effect. S/p ratios also vary seasonally in the red knot Calidris canutus and are higher in birds newly arrived in breeding areas than at other times. If that increase was an adaptive response to promote wing‐lifting in association with various breeding behaviors as suggested, one would expect it to result from an absolute increase in the post‐arrival size of the supracoracoideus, which was not observed. Instead, we propose that it is unrelated to enhancing the upstroke but results from a decrease in the size of the pectoralis, which is a consequence of the greater rate at which this muscle is catabolized in times of exertion and stress, as at the end of a long migration or during starvation. Fuller data on the size, morphology and physiology of individual muscles at various stages of the annual cycle and migration will help to clarify how ratio changes are achieved, and evaluate potential adaptive significance.
      PubDate: 2014-11-06T09:12:26.34457-05:0
      DOI: 10.1111/jav.00506
  • Testis asymmetry in birds: the influences of sexual and natural selection
    • Authors: Sara Calhim; Robert Montgomerie
      Abstract: Gonad size and shape asymmetries are particularly common in birds. Although some obvious size and shape differences between the left and right testes in birds were first documented more than a century ago, little is known about what influences the variation across species in either the degree or the direction of these asymmetries. Here we show that a left bias in size is the most likely ancestral state in most orders and families, and that there is a weak but significant negative relation between the degree of size and shape asymmetries. In extant species, testis size and shape symmetries increase with the degree of sperm competition (relative testes mass), but those relations are significant only in those species with left bias in each of these traits. When space is particularly constrained on the left side of the body cavity due to a large gizzard (e.g. in granivores), the left testis is more elongated and the degree of size symmetry is larger. Despite significant patterns, relative testes mass and gizzard complexity together explain < 10% of the variation in testis asymmetry in species with left biases. Thus our analyses suggest that some other factor is largely responsible for the evolution of gonad asymmetry in birds: 1) that a left bias in testis size might be a correlated response to selection for a left bias in the development of a single (left) ovary in females of most bird species, and/or 2) that physiological efficiency due to the dramatic and rapid increase in testis size of most species during the breeding season might favour enlargement of one testis. Our conclusions highlight the need to rethink and improve our understanding of the physiological processes underlying the investment in gonads by male birds.
      PubDate: 2014-10-15T09:42:13.153406-05:
      DOI: 10.1111/jav.00503
  • Systematics and evolution of the Pan‐Alcidae (Aves, Charadriiformes)
    • Authors: N. Adam Smith; Julia A. Clarke
      Pages: n/a - n/a
      Abstract: Puffins, auks and their allies in the wing‐propelled diving seabird clade Pan‐Alcidae (Charadriiformes) have been proposed to be key pelagic indicators of faunal shifts in Northern Hemisphere oceans. However, most previous phylogenetic analyses of the clade have focused only on the 23 extant alcid species. Here we undertake a combined phylogenetic analysis of all previously published molecular sequence data (∼ 12 kb) and morphological data (n = 353 characters) with dense species level sampling that also includes 28 extinct taxa. We present a new estimate of the patterns of diversification in the clade based on divergence time estimates that include a previously vetted set of twelve fossil calibrations. The resultant time trees are also used in the evaluation of previously hypothesized paleoclimatic drivers of pan‐alcid evolution. Our divergence dating results estimate the split of Alcidae from its sister taxon Stercorariidae during the late Eocene (∼ 35 Ma), an evolutionary hypothesis for clade origination that agrees with the fossil record and that does not require the inference of extensive ghost lineages. The extant dovekie Alle alle is identified as the sole extant member of a clade including four extinct Miocene species. Furthermore, whereas an Uria + Alle clade has been previously recovered from molecular analyses, the extinct diversity of closely related Miocepphus species yields morphological support for this clade. Our results suggest that extant alcid diversity is a function of Miocene diversification and differential extinction at the Pliocene–Pleistocene boundary. The relative timing of the Middle Miocene climatic optimum and the Pliocene–Pleistocene climatic transition and major diversification and extinction events in Pan‐Alcidae, respectively, are consistent with a potential link between major paleoclimatic events and pan‐alcid cladogenesis.
      PubDate: 2014-10-10T03:34:25.839682-05:
      DOI: 10.1111/jav.00487
  • Long‐term phenological shifts and intra‐specific differences
           in migratory change in the willow warbler Phylloscopus trochilus
    • Authors: Johanna S. U. Hedlund; Sven Jakobsson, Cecilia Kullberg, Thord Fransson
      Pages: n/a - n/a
      Abstract: Climate change can influence many aspects of avian phenology and especially migratory shifts and changes in breeding onset receive much research interest in this context. However, changes in these different life‐cycle events in birds are often investigated separately and by means of ringing records of mixed populations. In this long‐term study on the willow warbler Phylloscopus trochilus, we investigated timing of spring and autumn migration in conjunction with timing of breeding. We made distinction among individuals with regard to age, sex, juvenile origin and migratory phase. The data set comprised 22‐yr of ringing records and two temporally separated data sets of egg‐laying dates and arrival of the breeding population close to the ringing site. The results reveal an overall advancement consistent in most, but not all, phenological events. During spring migration, early and median passage of males and females became earlier by between 4.4 to 6.3 d and median egg‐laying dates became earlier by 5 d. Male arrival advanced more, which may lead to an increase in the degree of protandry in the future. Among breeding individuals, only female arrival advanced in timing. In autumn, adults and locally hatched juvenile females did not advanced median passage, but locally hatched juvenile males appeared 4.2 d earlier. Migrating juvenile males and females advanced passage both in early and median migratory phase by between 8.4 to 10.1 d. The dissimilarities in the response between birds of different age, sex and migratory phase emphasize that environmental change may elicit intra‐specific selection pressures. The overall consistency of the phenological change in spring, autumn and egg‐laying, coupled with the unchanged number of days between median spring and autumn migration in adults, indicate that the breeding area residence has advanced seasonally but remained temporally constant.
      PubDate: 2014-10-10T03:34:10.821314-05:
      DOI: 10.1111/jav.00484
  • Survival of Gunnison sage‐grouse Centrocercus minimus in Colorado,
    • Authors: Amy J. Davis; Michael L. Phillips, Paul F. Doherty
      Pages: n/a - n/a
      Abstract: Gunnison sage‐grouse Centrocercus minimus has declined from their historic range and recent monitoring has provided evidence that some populations are continuing to decline. The evaluation of long‐term, population‐specific survival rates is important to assess population stability, and is necessary for conservation of this species of concern. We evaluated adult and yearling survival in two dynamically different populations of Gunnison sage‐grouse (a relatively large, more stable population and a small, declining population). Our goal was to examine the relationship between annual survival and population, and test hypotheses with regards to temporal effects (across years and within year) and individual effects (sex and age). We also evaluated the effects of snow depth on sage‐grouse survival. We tracked 214 radiomarked birds in the large population from 2005–2010 and 25 birds in the small population from 2007–2010. We found no evidence for a difference in survival between yearlings and adults nor did we find an influence of snow depth on survival. Males had the lowest survival during the lekking season (March–April); females had lower survival during the nesting and chick rearing season (May–July) and late‐summer and fall (August–October). The annual survival rate was 0.61 (SE 0.06) for females and 0.39 (SE 0.08) for males. Survival was constant across years and between the populations suggesting observed population changes during this time period are not a result of changes in adult survival.
      PubDate: 2014-10-10T03:33:56.653144-05:
      DOI: 10.1111/jav.00473
  • The decline of a peripheral population of the European robin Erithacus
    • Authors: José Luis Tellería
      Pages: n/a - n/a
      Abstract: This paper examines the potential effect of some factors involved in the decline of a winter population of the European robin Erithacus rubecula in southern Spain. The area receives extra‐Iberian immigrants that come into contact with resident conspecifics. Given this interspersed distribution, three hypotheses were tested to explain the decline: a) the depletion of the carrying capacity of the area during winter, b) the decline of the resident population, and c) the reduction of foreign individuals in this wintering area. Winter robin and fruit (a main winter food) abundances were assessed at 43 sites from 1999 to 2014, and the abundance of breeding robins was evaluated from 1998 to 2012. Rainfall and temperatures were recorded throughout this period and changes in forests occupied by breeding robins were assessed in 1999 and 2013. Results showed a decline in winter temperatures and an increase in fruit availability. Given that food increases could buffer the thermoregulatory costs of colder conditions, the depletion of the carrying capacity of the area was discarded as a main driver of robin decline. Spring counts showed a reduction of 45% in the breeding population that was not explained by changes in forest management. However, a significant increase in summer temperatures could boost the pervasive effect of drought on robins inhabiting this marginal area of the species' range. Foreign immigrants, despite the increase in breeding populations in most of Europe, did not buffer the decline caused by the reduction of residents. In fact, an analysis of ring recoveries reported in this area depicted a sharp decrease in extra‐Iberian wintering individuals. These results may be related to the effect of global warming on migratory schedules (the northwards retreat of wintering areas) and on the suitability for robins of local habitats in this peripheral region of the Palaearctic.
      PubDate: 2014-10-10T03:32:32.672192-05:
      DOI: 10.1111/jav.00451
  • House sparrow Passer domesticus survival is not associated with
           MHC‐I diversity, but possibly with specific MHC‐I alleles
    • Authors: Maria Karlsson; Julia Schroeder, Shinichi Nakagawa, Henrik G. Smith, Terry Burke, Helena Westerdahl
      Pages: n/a - n/a
      Abstract: The MHC (Major Histocompatibility Complex) plays an important role in the immune system of vertebrates. MHC genes are extremely polymorphic and this variation is considered to be maintained by selection from pathogens. We investigate whether MHC diversity (number of different alleles per individual) affects the survival and recruitment of nestling house sparrows. We hypothesize that individuals with higher MHC diversity can recognize and combat a wider range of pathogens, and therefore are more likely to survive and recruit into the breeding population. Additionally, we hypothesize that specific MHC class I alleles (MHC‐I) could be associated with survival and recruitment. We screened MHC‐I genotypes in 518 house sparrow chicks hatched on Lundy Island but we found no evidence for a relationship between nestling survival, post‐fledging survival or recruitment success with MHC diversity. Then we investigated effects of specific MHC‐I alleles in 195 individuals from a single cohort. Twenty‐one MHC‐I alleles were tested for relationships with nestling survival, post‐fledging survival and recruitment, and we detected associations with survival for three different alleles. This pattern was, however, not different to what would be expected from random, so we could not conclude that particular MHC‐I alleles are associated with survival in house sparrows on Lundy Island. Nonetheless, one of these alleles (1105) showed both a tendency for a higher probability of surviving in nestlings, and a significant association with survival in fledglings. We envision that allele 1105 could be an interesting candidate gene for testing associations with survival in house sparrows in the future.
      PubDate: 2014-10-10T03:32:18.953319-05:
      DOI: 10.1111/jav.00413
  • Neighbour recognition in two sister songbird species with a simple and
           complex repertoire – a playback study
    • Authors: Pavel Jaška; Pavel Linhart, Roman Fuchs
      Abstract: The ability of individuals to recognize others based on vocalizations has been proven in many species of birds. However, we are still far from understanding important aspects of the discrimination process. For example, it is still not fully understood whether, and why, repertoire size hinders discrimination between individuals. Further, the strategies and vocal cues used for discrimination between individuals are largely unexplored. In this study, we tested the ability of chiffchaffs Phylloscopus collybita and willow warblers Phylloscopus trochilus, two closely related species with different repertoire sizes and song organization, to differentiate between their neighbours on the basis of a single song of a neighbouring male. We did playback experiments within the ‘dear enemy’ paradigm in which we tested resident males with a single song of a neighbour broadcast from the correct and opposite, incorrect territory border. Both species displayed a strong ability to discriminate between their neighbours representing further evidence that repertoire size per se has no negative impact on individual recognition in songbirds. Using a single song for playback allowed us to speculate about the nature of the possible cues used by males for recognition. Individual recognition in both species is most likely based on the modulation of syllables or on general voice characteristics. We suggest that specific changes in song organization, for example the tendency of individuals to insert a distinct phrase at the beginning of each song, may facilitate individual recognition and compensate for increased repertoire size in willow warblers.
      PubDate: 2014-09-30T06:56:40.800782-05:
      DOI: 10.1111/jav.00482
  • Automated tracking of wild hummingbird mass and energetics over multiple
           time scales using radio frequency identification (RFID) technology
    • Authors: Lily Hou; Michael Verdirame, Kenneth C. Welch
      First page: 1
      Abstract: We examined the feasibility of automating the collection of hummingbird mass data facilitated by low‐cost, low‐power radio frequency identification (RFID) technology. In a field study in southern Ontario, wild hummingbirds were captured, subcutaneously implanted with passive integrated transponder (PIT) tags, and released over a three‐year period. Tagged hummingbirds were detected at specially designed feeder stations outfitted with low‐cost, low‐power RFID readers coupled with a perch secured to a digital balance. When tagged birds visited the feeder, transponder detection initiated the recording of the perched hummingbird's mass at regular intervals continuing as long as the bird remained. This permitted a nearly continuous record of mass during each visit. Mass data collected from tagged hummingbirds showed consistent trends at multiple temporal scales: the individual feeder visit, single days, and even whole seasons. These results further confirm that RFID technology is safe for use in the smallest birds. The effective detection range is a function of RFID reader power, antenna, and tag size. Yet, we find that careful arrangement of feeders and detectors allows for reliable detection even when detection range is low. When coupled with additional technologies, such as a precision electronic balance, this approach can yield robust serial measures of physiological parameters such as mass, an indicator of energy balance over time.
      PubDate: 2014-09-08T07:34:56.462379-05:
      DOI: 10.1111/jav.00478
  • Sexual pigmentation and parental risk‐taking in yellow warblers
           Setophaga petechia
    • Authors: Andrea S. Grunst; Melissa L. Grunst, John T. Rotenberry
      First page: 9
      Abstract: Adult‐directed predation risk imposes important behavioral constraints on parents and might thus alter relationships between costly sexual ornaments and parental performance. For instance, under low predation risk, highly ornamented individuals might display better parental performance than others, as predicted by ‘good parent’ models of sexual selection. However, under high risk of predation, highly ornamented individuals might abandon parental effort if conspicuous to predators, or if social partners are more willing to take parental risks when paired with highly ornamented mates. We experimentally elevated perceived adult‐directed predation risk near nests to explore how carotenoid‐ and phaeomelanin‐based pigmentation in both sexes relate to parental risk‐taking for offspring in the yellow warbler Setophaga petechia. Compared to other males, males with more intense carotenoid‐based pigmentation maintained higher levels of paternal effort under predation risk at highly concealed nests, but reduced nestling provisioning rate more at exposed nests. Further, when faced with predation risk, females with more phaeomelanin‐based pigmentation reduced nestling provisioning rate less than other females, regardless of nest concealment. Females displayed higher parental effort across treatments when paired to males with more colorful carotenoid pigmentation. However, birds did not reduce parental effort under risk less when paired to a highly ornamented mate, suggesting that predation risk did not accentuate differential allocation. Males did not take fewer parental risks than females. Results indicate that nest concealment modifies parental risk‐taking by males with colorful carotenoid‐based pigmentation, and suggest that female melanin‐based pigmentation may indicate boldness and greater a propensity to take parental risks.
      PubDate: 2014-09-08T07:35:09.534906-05:
      DOI: 10.1111/jav.00496
  • Nutritional stress affects corticosterone deposition in feathers of
           Caspian tern chicks
    • Authors: Allison G. L. Patterson; Alexander S. Kitaysky, Donald E. Lyons, Daniel D. Roby
      First page: 18
      Abstract: Stressful environmental conditions affect the adrenocortical function of developing animals, which can have consequences for their fitness. Discovery of the avian stress hormone corticosterone (CORT) in feathers has the potential to broaden the application of endocrine research in ecological and evolutionary studies of wild birds by providing a long‐term measure of CORT secretion. Mechanisms of CORT deposition in feathers are not well known and few studies have related feather CORT to circulating plasma CORT during feather growth. Our objective was to experimentally test the validity of using feather CORT as a measure of CORT secretion in developing birds experiencing nutritional stress. Caspian tern Hydroprogne caspia chicks were fed ad libitum or restricted (35% less than ad libitum) diets for four weeks. We measured CORT in feathers from these chicks to examine the relationship between feather CORT concentrations and nutritional limitation, circulating plasma CORT, and feather development. We found that feather CORT was higher in controls fed ad libitum than in restricted individuals, despite higher levels of plasma CORT in restricted chicks compared to controls. Feather mass and growth rates were strongly and positively related to feather CORT concentrations in both treatments. This is the first experimental study to show that feather CORT concentrations can be lower in response to nutritional stress, even when plasma CORT concentrations are elevated. Our results indicate that CORT deposition in feathers may be confounded when feather mass and growth rates are compromised by nutritional stress. We conclude that feather CORT can be used for assessing nutritional stress in growing birds, but the direction of response depends on how strongly stress affects feather development.
      PubDate: 2014-07-09T07:43:45.970039-05:
      DOI: 10.1111/jav.00397
  • Regional and seasonal flight speeds of soaring migrants and the role of
           weather conditions at hourly and daily scales
    • Authors: W. M. G. Vansteelant; W. Bouten, R. H. G. Klaassen, B. J. Koks, A. E. Schlaich, J. van Diermen, E. E. van Loon, J. Shamoun‐Baranes
      First page: 25
      Abstract: Given that soaring birds travel faster with supportive winds or in good thermal soaring conditions, we expect weather conditions en route of migration to explain commonly observed regional and seasonal patterns in the performance of soaring migrants. We used GPS‐loggers to track 13 honey buzzards and four Montagu's harriers for two to six migrations each. We determined how tailwinds, crosswinds, boundary layer height (a proxy for thermal convection) and precipitation affected hourly speeds, daily distances and daily mean speeds with linear regression models. Honey buzzards mostly travel by soaring while Montagu's harriers supplement soaring with flapping. Therefore, we expect that performance of harriers will be less affected by weather than for buzzards. Weather conditions explained between 30 and 50% of variation in migration performance of both species. Tailwind had the largest effect on hourly speeds, daily mean speeds and daily travel distances. Honey buzzards travelled significantly faster and farther, and Montagu's harriers non‐significantly faster, under better convective conditions. Honey buzzards travelled at slower speeds and shorter distances in crosswinds, whereas harriers maintained high speeds in crosswinds. Weather conditions varied between regions and seasons, and this variation accounted for nearly all regional and seasonal variation in flight performance. Hourly performance was higher than predicted at times when we suspect birds had switched to intermittent or continuous flapping flight, for example during sea‐crossings. The daily travel distance of Montagu's harriers was determined to a significant extent by their daily travel time, which differed between regions, possibly also due to weather conditions. We conclude with the implications of our work for studies on migration phenology and we suggest an important role for high‐resolution telemetry in understanding migratory behavior across entire migratory journeys.
      PubDate: 2014-08-01T03:11:51.251805-05:
      DOI: 10.1111/jav.00457
  • Body‐mass‐dependent trade‐off between immune response
           and uropygial gland size in house sparrows Passer domesticus
    • Authors: Gregorio Moreno‐Rueda
      First page: 40
      Abstract: Parasites greatly impact host fitness. The immune system is fundamental to combat endoparasites, and survival increases with greater investment in immunity. Some ectoparasites, by contrast, are reportedly combated by the use of the uropygial gland, an organ exclusive to birds, which secretes an oily substance (preen oil) that is spread on plumage. However, both mounting an immune response against a parasite and producing uropygial gland secretion depend on the same resources, a situation which may induce trade‐offs between the two antiparasitic functions. In this study, I experimentally test whether immune response is traded off against uropygial gland size in the house sparrow Passer domesticus. In the experiment, a group of sparrows were injected with an antigen (lipopolysaccharide, LPS), which stimulates the immune system, while the other group received a sham injection. The uropygial gland of LPS‐treated birds decreased significantly more than that of the control birds after treatment. Nevertheless, the effect of the treatment was limited to house sparrows with low body mass, suggesting that heavy house sparrows were able to produce an immune response while maintaining a relatively large uropygial gland. Given that uropygial gland size is strongly related to production of preen oil, these results suggest that preen oil production declines in birds in poor body condition when resources are preferentially diverted to other demanding functions, such as the immune system. Considering that the uropygial gland is involved in several fitness‐related processes in birds, the trade‐off between immune response and uropygial gland size may have important consequences for bird life histories.
      PubDate: 2014-07-24T04:22:17.032446-05:
      DOI: 10.1111/jav.00358
  • Laying‐sequence variation in yolk carotenoids and egg
           characteristics in the red‐winged blackbird Agelaius phoeniceus
    • Authors: Jennifer L. Newbrey; Cynthia A. Paszkowski, Kevin J. McGraw, Susanna Ogle
      First page: 46
      Abstract: In many bird species with asynchronous hatching, smaller, later‐hatched nestlings are out‐competed for food by their larger, earlier‐hatched siblings and therefore suffer increased mortality via starvation. It is thought that female birds can either maintain or reduce the survival disadvantage of later‐hatched nestlings by differentially allocating maternal resources across the eggs of a clutch. Carotenoid pigments are an example of resources that female birds allocate differentially when producing a clutch, but laying sequence patterns for these pigments remain poorly studied in North American songbirds. We examined intraclutch variation in yolk carotenoids and egg metrics in 27 full clutches of red‐winged blackbird Agelaius phoeniceus eggs collected from eight wetlands in central Alberta, Canada. We predicted that carotenoids would decrease across the laying sequence, as in this species, later‐hatched, marginal nestlings suffer greater mortality than earlier‐hatched, core nestlings. We found nine carotenoid pigments in red‐winged blackbird egg yolks, including two that have never been described from avian yolks: α‐doradexanthin and adonirubin. As predicted, concentrations and amounts of most carotenoids decreased across the laying sequence, suggesting that female red‐winged blackbirds depleted their carotenoid resources as they laid more eggs. However, egg mass and yolk mass both increased across the laying sequence, suggesting that female red‐winged blackbirds may use other maternal resources to compensate for the size and survival disadvantage experienced by later‐hatched, marginal nestlings.
      PubDate: 2014-07-24T04:22:14.690207-05:
      DOI: 10.1111/jav.00332
  • Song‐based species discrimination in a rapid Neotropical radiation
           of grassland seedeaters
    • Authors: Pilar Benites; Leonardo Campagna, Pablo L. Tubaro
      First page: 55
      Abstract: Acoustic signals among newly diverged taxa have the potential to convey species identity, information that is key to reducing hybridization. Capuchino seedeaters constitute a remarkable example of recently radiated endemic species from the grasslands of South America. They are sexually dimorphic and show striking differences in male plumage coloration and song. Contrasting with this divergence in phenotype most species show extremely low neutral genetic differentiation and lack of reciprocal monophyly, which is interpreted to be a product of recent common ancestry and hybridization. Here we use field‐based playback experiments to test for the first time if males of two species, Sporophila hypoxantha and S. palustris, discriminate between conspecific and heterospecific song. Using various measures of behavior we find that both species react more strongly to their own songs. The response to playback from another southern capuchino cannot be differentiated from that of a control song from a more distantly related Sporophila species. Additionally, we did not find evidence for reinforcement as the response of S. hypoxantha did not differ between individuals that co‐occur with S. palustris and those that do not. Our finding suggests that song, a culturally inherited trait, may help maintain reproductive isolation between species in the rapid and explosive capuchino radiation.
      PubDate: 2014-07-24T04:22:19.368748-05:
      DOI: 10.1111/jav.00447
  • Impacts of climate and land‐use change on wintering bird populations
           in Finland
    • Authors: Sara Fraixedas; Aleksi Lehikoinen, Andreas Lindén
      First page: 63
      Abstract: Few studies have covered both the effects of climate and land‐use change on animal populations under a single framework. Besides, the scarce multi‐species studies conducted have focused on breeding data, and there is little information published on changes in wintering populations. Here, we relate the pattern of long‐term temporal trends of wintering bird populations in Finland, north Europe, to covariates associated with climate and land‐use change. Finnish wintering populations have been monitored using ca 10 km winter bird census routes (> 420 routes counted annually) during 1959–2012. Population trends of 63 species were related to migratory strategy, urbanity, and thermal niche measured as species‐specific centre of gravity of the wintering distribution. Waterbird trends have shown a marked increase compared to landbirds. Among landbirds, forest species have suffered severe declines, whereas urban species have considerably increased in their wintering numbers. To follow up these results, we produced three multi‐species indices (for waterbirds, forest and urban species, respectively), which can improve our ability to detect and monitor the specific consequences of climate change and changes in land‐use, but at the same time act as a feedback to track the conservation status of the species. Our results suggest that waterbirds are responding to climate change, given their dependence on open water and the correlation with early‐winter temperature over the last decades. On the other hand, we believe trends of landbirds have been mainly driven by human‐induced land‐use changes. While urban species have likely benefited from the increase of supplementary feeding, forest species have probably suffered from the loss of native habitats.
      PubDate: 2014-09-08T07:29:30.324774-05:
      DOI: 10.1111/jav.00441
  • Factors influencing migratory decisions made by songbirds on spring
    • Authors: Kristen M. Covino; Rebecca L. Holberton, Sara R. Morris
      First page: 73
      Abstract: Behavioral decisions made by migrating songbirds may depend on a variety of biotic and abiotic factors. To investigate which factors most influence songbird behavior on stopover, we related departure and directional decisions of captive birds released at the capture site to a variety of factors including, weather, date, energetic condition, age, sex, and species. We captured spring migrants during the day, released them after sunset, and visually assessed whether they departed the study site and if so, in which direction. Departure was strongly influenced by wind direction and energetic condition, especially fat stores. The proportion of birds departing increased as the season progressed. Directional decisions were also strongly influenced by energetic condition, particularly fat stores and plasma triglyceride levels. Wind direction also influenced the direction in which birds made migratory flights. While energetic condition, stage of migration, and weather seem to be important proximate determinants in departure and directional decisions, habitat availability and other factors may also need to be considered.
      PubDate: 2014-09-30T06:56:03.314627-05:
      DOI: 10.1111/jav.00463
  • Availability of optimal‐sized prey affects global distribution
           patterns of the golden eagle Aquila chrysaetos
    • Authors: Andreas Schweiger; Hans‐Joachim Fünfstück, Carl Beierkuhnlein
      First page: 81
      Abstract: Climate and landscape change are expected to significantly affect trophic interactions, which will especially harm top predators such as the golden eagle Aquila chrysaetos. Availability of optimal prey is recognized to influence reproductive success of raptors on a regional scale. For the golden eagle, medium‐sized prey species between 0.5 and 5 kg are widely considered to be optimal prey during the breeding season, whereas smaller and larger species are deemed as energetically sub‐optimal. However, knowledge about the effects of optimal prey availability is still scarce on larger scales. To decrease this apparent knowledge gap, we combined biogeographical information on range margins with information about the foraging behaviour and reproductive success of golden eagles from 67 studies spanning the Northern Hemisphere. We hypothesized that availability of optimal prey will affect foraging behaviour and breeding success and, thus, distribution patterns of the golden eagle not only on a local but also on a continental scale. We correlated the diet breadth quantifying foraging generalism, breeding success and proportions of small (< 0.5 kg), medium (0.5–5 kg) and large‐sized (> 5 kg) prey species within the diet with the minimum distance of the examined eagles to the actual species distribution boundary. Closer to the range edge, we observed decreased proportions of medium‐sized prey species and decreasing breeding success of golden eagles. Diet breadth as well as proportions of small and large‐sized prey species increased, however, towards the range edge. Thus, availability of optimal‐sized prey species seems to be a crucial driver of foraging behaviour, breeding success and distribution of golden eagles on a continental scale. However, underlying effects of landscape characteristics and human influence on optimal prey availability has to be investigated in further large‐scale studies to fully understand the major threats facing the golden eagle and possibly other large terrestrial birds of prey.
      PubDate: 2014-09-08T07:29:17.549849-05:
      DOI: 10.1111/jav.00396
  • Nutritional composition of the preferred prey of insectivorous birds:
           popularity reflects quality
    • Authors: Emma Razeng; David M. Watson
      First page: 89
      Abstract: Food availability is emerging as a key determinant of avian occurrence and habitat use in a variety of systems, but insectivores have received less attention than other groups and the potential influence of nutritional quality has rarely been considered. Rather than a uniform food source, arthropods vary greatly in terms of nutritional composition, but does this variation translate into differential consumption' Building on previous work that demonstrated clear preference for some arthropod groups by 13 species of ground‐foraging insectivores, we compare the nutritional composition of these arthropod groups with other groups commonly encountered but seldom consumed in the same habitat types. Using samples of arthropods collected from a eucalypt woodland in southern Australia, we found the high frequency prey groups (Coleoptera, Lepidoptera, Orthoptera and Araneae) consistently contained higher fractions of crude protein and total fat than the low frequency groups (Diptera, Hymenoptera and Odonata). Even more clear‐cut differences were noted in terms of micronutrients; high frequency prey containing significantly greater concentrations of seven elements than low frequency prey and significantly greater amounts per individual arthropod for all eleven elements measured. These results indicate that the nutritional quality plays an important role in prey selection in insectivores and suggests that micronutrients may be more important determinants of prey choice than previously recognized. Integrating these findings with previous work suggesting food limitation may constrain distribution patterns of birds in fragmented landscapes, we contend that variation in nutritional quality helps explain observed patterns in insectivore diets and occurrence. In addition to explaining why smaller and more disturbed habitats are unable to support resident insectivore populations, this bottom‐up mechanism may underlie the disproportionate sensitivity of insectivores to land‐use intensification.
      PubDate: 2014-09-30T06:56:19.843861-05:
      DOI: 10.1111/jav.00475
  • Hatching date vs laying date: what should we look at to study avian
           optimal timing of reproduction'
    • Authors: Gustavo Tomás
      First page: 107
      Abstract: Most research conducted on optimal timing of reproduction in birds has traditionally considered laying date of the first egg as the event that needs to be related to the time of maximum food availability. However, what (most) birds need to time with the seasonal peak of food availability is the moment of maximum food demand of their nestlings, which is more tightly related with hatching date than with laying date. After initiating egg laying, birds still have some opportunities to adjust the time of highest food demand, as during the several days elapsed between laying of the first egg until hatching, more precise cues will become available to birds in order to make a more accurate match with food availability. I provide an overview of the suite of mechanisms available to birds for shortening or enlarging the interval between laying and hatching date, which include laying gaps, adjustment of clutch size, variation in onset and intensity of incubation, and differential investment on eggs. Then I illustrate with an example the extent to which birds can adjust hatching dates after egg laying. I argue that birds should more accurately time hatching date rather than laying date to maximum food availability on the basis of available cues. Therefore, I suggest that researchers should target on hatching date rather than laying date to better study optimal timing of reproduction in birds. Exploration of responses other than adjusting laying date to changing environmental conditions will surely uncover key aspects of avian reproductive biology and behaviour that have been ignored until now. This is a necessary step towards a better understanding of capacities of organisms to adapt to a changing world in particular, and of fitness consequences of timing of reproduction in general.
      PubDate: 2014-09-08T07:29:42.610853-05:
      DOI: 10.1111/jav.00499
  • Allelic variation at innate immune genes (avian β‐defensins),
           with in a natural population of great tits
    • Authors: Olof Hellgren
      First page: 113
      Abstract: In order to fully understand pathogen induced natural variation in fitness in wild animal populations it is important to identify and study the degree of non‐synonymous alleles in genes that code for components of the immune system. This study investigates the degree of natural genetic variation at 6 innate immune genes belonging to the β‐defensin family within a single population of birds, the great tits Parus major. In 40 adult individuals, all belonging to the same local population in Wytham Woods, Oxford, UK, screened across 6 different β‐defensin genes, all but one individual showed non‐synonymous heterozygosity within the exon coding for the mature defensin peptide. The non‐synonomous variation was thus associated with the part of the defensin gene that directly interacts with potential pathogens. Within the sample, 31 different genotypes were identified across the 6 different loci. Much of the found allelic variation affected the amino acid composition, which in turn alter the net charge and hydrophilicity of the produced peptide; properties associated with the efficiency of binding to and rupture pathogens. This study demonstrates that non‐synonymous genetic variation exists at β‐defensins genes, a part of the immune system that forms an important first line of defence against various pathogens. Understanding the degree of underlying genetic variation at different parts of the immune system will help achieve a holistic view of the reasons behind individual variation in pathogen susceptibility, as well as why individuals are affected differently once they become infected.
      PubDate: 2014-10-15T09:41:59.118103-05:
      DOI: 10.1111/jav.00370
  • Seasonal mortality and sequential density dependence in a migratory bird
    • Abstract: Migratory bird populations may be limited during one or more seasons, and thus at one or more places, but there is a dearth of empirical examples of this possibility. We analyse seasonal survival in a migratory shellfish‐eating shorebird (red knot Calidris canutus islandica) during a series of years of intense food limitation on the nonbreeding grounds (due to overfishing of shellfish stocks), followed by a relaxation period when destructive harvesting had stopped and food stocks for red knots recovered. For the estimation of seasonal survival from the 15 yr‐long near‐continuous capture–resight dataset, we introduce a ‘rolling window’ approach for data exploration, followed by selection of the best season definition. The average annual apparent survival over all the years was 0.81 yr−1. During the limitation period, survival probability of adult red knots was low in winter (0.78 yr−1), but this was compensated by high survival in summer (0.91 yr−1). During the relaxation period survival rate levelled out with a winter value of 0.81 yr−1 and a summer survival of 0.82 yr−1. The fact that during the cockle‐dredging period the dip in survival in winter was completely compensated by higher survival later in the annual cycle suggests sequential density dependence. We conclude that seasonal compensation in local survival (in concert with movements to areas apparently below carrying capacity) allowed the islandica population as a whole to cope, in 1998–2003, with the loss of half of the suitable feeding habitat in part of the nonbreeding range, the western Dutch Wadden Sea. As a more general point, we see no reason why inter‐seasonal density dependence should not be ubiquitous in wildlife populations, though its limits and magnitude will depend on the specific ecological contexts. We elaborate the possibility that with time, and in stable environments, seasonal mortality evolves so that differences in mortality rates between seasons would become erased.
  • Loss of sexual dimorphism is associated with loss of lekking behavior in
           the green manakin Xenopipo holochora
    • Abstract: Manakins (Pipridae) are well know for elaborate male sexual displays and ornate plumage coloration, both of which are thought to have evolved as a consequence of lekking breeding, the prevalent mating system in the family. Less attention has been paid to a handful of ‘drab’ manakin species, in which sexual dimorphism appears to be reduced or absent. Using character reconstruction, we show that these ‘exceptions to the rule’ represent phylogenetically independent cases of losses in sexual dimorphism, and as such could provide a focal group to investigate the link between changes in morphology and in life history (e.g. mating system). We take a first step in this direction by focusing on two subspecies of the putatively monomorphic green manakin Xenopipo holochlora to formally confirm that the species is sexually monomorphic in size and plumage color and test the prediction that sexual monomorphism is associated with the loss of lekking behavior in this species. Our results show that size dimorphism is present but limited in the green manakin, with substantial overlap in male and female morphometric measures, and that sexes are largely monochromatic (including from an avian perspective), despite marked coloration differences between subspecies. Behavioral observations indicate that males do not form leks and do not engage in elaborate sexual displays, that there is no stable pair bond formation, and that females provide parental care alone. These findings are consistent with the idea that changes in mating behavior may have driven changes in morphology in Pipridae, and we encourage similar studies on other drab manakins to better understand this relationship.
  • Always together: mate guarding or predator avoidance as determinants of
           group cohesion in white‐breasted mesites'
    • Abstract: Being a member of a cohesive group can have fitness benefits such as decreased predation risk, increased feeding efficiency as well as enhanced access to social information and mates. However, competition and the risk of parasite transmission exert centrifugal forces on group‐living. Thus, the actual degree of cohesion is expected to vary as a function of the relative importance of several social and ecological factors. White‐breasted mesites Mesitornis variegata are medium‐sized ground‐dwelling birds endemic to the dry deciduous forests of western Madagascar. They live in stable breeding pairs or small family groups, mate monogamously and often form temporary heterospecific associations with canopy‐dwelling bird species that give alarm calls to which mesites respond with anti‐predator behaviours. We investigated the potential effects of predation risk and mate defence on mesite group cohesion by analysing inter‐individual distances of 20 groups as a function of mesite social organization, alarm call events, the size of associated heterospecific flocks, and the adults' reproductive state. Mesite social units were very cohesive, particularly in families, when associated with smaller heterospecific flocks, and after an alarm call event. Adult reproductive state did not influence breeding partners' cohesion. Therefore, the pronounced group cohesion in mesites seems to be mainly a response to the high predation risk typically associated with a terrestrial life‐style, and not to mate‐guarding. However, we suggest that high group cohesion due to predation risk could limit opportunities for solitary extra‐territorial forays to obtain extra‐pair copulations, thereby contributing to a strictly monogamous system in this species.
  • Ecological and environmental factors related to variation in egg size of
           New World flycatchers
    • Abstract: Geographical variation in egg size is well documented for several taxa, but remains insufficiently described for birds in spite of a well‐known latitudinal gradient in clutch size. Several hypotheses have been proposed to explain avian egg size variation; however, they were not tested on a continental scale. Egg size is a key component of reproductive investment that influences offspring fitness. It is thought to vary geographically as one of a set of correlated life‐history traits that are under selection from varying ecological conditions. We completed a comprehensive literature review and calculated egg sizes for the most widespread clade within tyrant flycatchers, describing for the first time the geographical variation in egg size on a continental scale. We examined the relative support for ecological and environmental variables in explaining egg size variation using multi‐model inference and linear mixed models controlled for phylogenetic autocorrelation among species. We tested five hypotheses and found that: larger eggs occur in colder sites, which is consistent with the embryonic temperature hypothesis; medium/long‐distance migrants had smaller eggs than resident species while short‐distance migrants had the largest eggs; neither species clutch size, nor species nest type, nor evapotranspiration seasonality influenced egg size. Avian egg size is larger in Austral and Neotropical America (ANA), where species are resident or short‐distance migrants, and smaller across the medium/long‐distance migrants of the Nearctic region. In addition, while clutch size increases towards higher northern latitudes and is almost invariable across ANA species, egg sizes vary largely across ANA sites, increasing with southern latitudes and higher elevations and being influenced by summer temperature. While the embryonic temperature hypothesis has been usually linked to parental nest attentiveness, we highlight that environmental temperatures also have strong effects in shaping investment in egg size.
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