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Journal of Avian Biology 
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ISSN (Print) 0908-8857 - ISSN (Online) 1600-048X
Published by John Wiley and Sons
[1587 journals]
[10 followers] Follow Subscription journalISSN (Print) 0908-8857 - ISSN (Online) 1600-048X
Published by John Wiley and Sons
[1587 journals]- Larger body size on islands affects silvereye Zosterops lateralis song and call frequency
- Authors: Dominique A. Potvin
Pages: no - no
Abstract: Differences in song repertoires and characteristics of island and mainland populations of the same avian species are usually explained by dispersal, cultural evolution and/or habitat differences. The influence of morphology is often overlooked, even though island populations are frequently morphologically distinct from mainland populations, and morphology could affect vocalizations. I compared morphological features, songs, contact calls and alarm calls of six isolated island populations of silvereye Zosterops lateralis with those of two mainland populations to examine whether differences between mainland and island vocalizations were consistent across vocalization types, and whether these differences could be linked to morphological differences. Vocalizations were lower in frequency on islands. Island individuals were larger (both in mass and body structure), and body mass was an important predictor of frequency in contact and alarm calls. I argue that this strong association results from the island rule (islands promote larger body sizes) and cascading effects of morphology on vocalization frequency in this species.
PubDate: 2013-02-27T11:33:44.408685-05:
DOI: 10.1111/j.1600-048X.2012.05820.x
- Authors: Dominique A. Potvin
- Great tits provided with ad libitum food lay larger eggs when exposed to colder temperatures
- Authors: Sonja V. Schaper; Marcel E. Visser
Pages: no - no
Abstract: The amount of nutrients deposited into a bird egg varies both between and within clutches of the same female. Larger eggs enhance offspring traits, but as a tradeoff, laying large eggs also infers energetic costs to the female. Income breeders usually lay larger eggs later in the season, when temperatures and food availability are higher. Egg size is thus affected by the daily amount of energy available to produce an egg under cold conditions, but it is less well known in how far temperature exerts direct effects on egg size. We show that great tit females Parus major with access to ad libitum food and breeding in climate‐controlled aviaries varied their egg investments. The size of an individual egg was best predicted by mean temperatures one week pre‐laying, with females laying larger, rather than smaller, eggs under colder conditions. Eggs increased in size over the season, but not significantly over the laying sequence. The degree of daily temperature fluctuation did not influence egg size. In addition to a substantial between‐female variation, sisters were more similar to each other than unrelated females, showing that egg size does also reflect heritable intrinsic female properties. Natural variation in egg size is thus not only determined by energy‐limitation, but also due to females allocating more resources to eggs laid in colder environments, thus increasing early survival of the chicks. That the positive correlation between temperature and egg investments that is found in a natural population is reversed under ad libitum food conditions demonstrates that wild great tits tradeoff own condition with survival prospects of their chicks as a function of available food, not ambient temperature.
PubDate: 2013-02-27T11:33:23.459285-05:
DOI: 10.1111/j.1600-048X.2012.00129.x
- Authors: Sonja V. Schaper; Marcel E. Visser
- Brown tawny owls moult more flight feathers than grey ones
- Authors: Patrik Karell; Jon E. Brommer, Kari Ahola, Teuvo Karstinen
Pages: no - no
Abstract: The mechanisms by which melanin‐based colour polymorphism can evolve and be maintained in wild populations are poorly known. Theory predicts that colour morphs have differential sensitivity to environmental conditions. Recently it has been proposed that colour polymorphism covaries genetically with intrinsic and behavioural properties. Plumage moult is a costly and crucial somatic maintenance function in birds. We used a long‐term data set consisting of 761 observations on 307 individuals captured between 1985 and 2010 to examine differences in partial flight feather moult between grey (pale) and brown (pheomelanic dark) colour morphs of the tawny owl. We find that the brown morph consistently moult more primary flight feathers than the grey morph whereas there is no clear difference between colour morphs in the moulting of secondary feathers. Contrary to expectations, the difference in the number of moulted flight feathers between the morphs was independent of environmental conditions, as quantified by the abundance of prey. We discuss the potential physiological and behavioural causes for and costs of the observed difference in maintenance functions between colour morphs.
PubDate: 2013-02-22T10:09:22.562867-05:
DOI: 10.1111/j.1600-048X.2012.05868.x
- Authors: Patrik Karell; Jon E. Brommer, Kari Ahola, Teuvo Karstinen
- Energetic consequences of contrasting winter migratory strategies in a sympatric Arctic seabird duet
- Authors: Jérôme Fort; Harald Steen, Hallvard Strøm, Yann Tremblay, Eirik Grønningsæter, Emeline Pettex, Warren P. Porter, David Grémillet
Pages: no - no
Abstract: At the onset of winter, warm‐blooded animals inhabiting seasonal environments may remain resident and face poorer climatic conditions, or migrate towards more favourable habitats. While the origins and evolution of migratory choices have been extensively studied, their consequences on avian energy balance and winter survival are poorly understood, especially in species difficult to observe such as seabirds. Using miniaturized geolocators, time‐depth recorders and a mechanistic model, we investigated the migratory strategies, the activity levels and the energy expenditure of the closely‐related, sympatrically breeding Brünnich's guillemots Uria lomvia and common guillemots Uria aalge from Bjørnøya, Svalbard. The two guillemot species from this region present contrasting migratory strategies and wintering quarters: Brünnich's guillemots migrate across the North Atlantic to overwinter off southeast Greenland and Faroe Islands, while common guillemots remain resident in the Barents, the Norwegian and the White Seas. Results show that both species display a marked behavioural plasticity to respond to environmental constraint, notably modulating their foraging effort and diving behaviour. Nevertheless, we provide evidence that the migratory strategy adopted by guillemots can have important consequences for their energy balance. Overall energy expenditure estimated for the non‐breeding season is relatively similar between both species, suggesting that both southward migration and high‐arctic winter residency are energetically equivalent and suitable strategies. However, we also demonstrate that the migratory strategy adopted by Brünnich's guillemots allows them to have reduced daily energy expenditures during the challenging winter period. We therefore speculate that ‘resident’ common guillemots are more vulnerable than ‘migrating’ Brünnich's guillemots to harsh winter environmental conditions.
PubDate: 2013-02-22T10:07:57.611127-05:
DOI: 10.1111/j.1600-048X.2012.00128.x
- Authors: Jérôme Fort; Harald Steen, Hallvard Strøm, Yann Tremblay, Eirik Grønningsæter, Emeline Pettex, Warren P. Porter, David Grémillet
- Gene‐flow across the European crow hybrid zone – a spatial simulation
- Authors: Anders Brodin; Fredrik Haas, Bengt Hansson
Pages: no - no
Abstract: In hybrid zones populations that are otherwise allopatric meet and produce hybrids. One of the most well‐known hybrid zones occurs throughout much of Europe between the hooded and carrion crows. Even though these species (or subspecies) of crows look very different, genetic differentiation is weak, and introgression seems to be common. In a spatial simulation that was based on empirically estimated values, we investigated how introgressing alleles that would confer some fitness advantage would flow across the zone. The advantage was assumed to be some unknown factor that enhanced survival for carriers relative to non‐carriers. We varied the yearly survival advantage between 0 to 10% and recorded how this would affect zone shape and position. In the simulation we cycled ‘yearly’ events such as reproduction, mortality and juvenile dispersal. We started the simulation by equipping all individuals of one crow type outside the zone with a homozygotic set of the beneficial allele. At all levels of advantage the allele first rapidly became fixed in the donator crow type, then transgressed into the receiving type more slowly and finally became fixed in all individuals. The time until fixation varied from around 176 yr for a 10% advantage to around 20 000 yr for 0% advantage. An exciting discovery was that the position of the zone would move during the introgression but then stop. The reason is that the beneficial allele would be common in the donating type but not in the receiving type during the introgression event. At large the crow hybrid zone appears to have been stable for a long time but there have been small recent northward movements of carrion crows in both Scotland and Denmark. We suggest that introgression by itself is a factor that should be considered as an explanation for why hybrid zones move temporarily.
PubDate: 2013-02-18T09:45:38.301228-05:
DOI: 10.1111/j.1600-048X.2012.00017.x
- Authors: Anders Brodin; Fredrik Haas, Bengt Hansson
- The effects of hatching date on timing of autumn migration in partial migrants – an individual approach
- Authors: Kalle Meller; Aleksi Lehikoinen, Anssi V. Vähätalo
Pages: no - no
Abstract: Timing of spring migration and breeding and their interaction with climate change has been widely studied in recent years, but the possible changes in timing of autumn migration have gained less attention. This work focuses on autumn migration and provides the first multi‐species individual‐based study of how hatching date affects the autumn migration date and migration age by using nestling ring data and re‐trappings of the same individuals during the autumn migration at the Hanko Bird Observatory, Finland. We studied three potentially multibrooded passerines (great tit, blue tit and coal tit) and two single‐brooded birds of prey (goshawk, sparrowhawk), all partially migratory short‐distance migrants. Individuals from late broods migrated at a younger age in all tit species and also in hawks the late hatched individuals tended to migrate at a younger age than the early‐hatched individuals. Late‐hatched individuals migrated later than early‐hatched individuals in blue and coal tits, where the latest hatchers represented second brood individuals. Based on our results, the time from hatching to autumn migration is not constant even among individuals of the same population. Our study indicates that climate warming induced advancement of avian breeding may cause changes in the timing of autumn migration through the frequency of second broods.
PubDate: 2013-02-18T09:45:33.092928-05:
DOI: 10.1111/j.1600-048X.2012.00016.x
- Authors: Kalle Meller; Aleksi Lehikoinen, Anssi V. Vähätalo
- Specialization to cold‐water upwellings may facilitate gene flow in seabirds: new evidence from the Peruvian pelican Pelecanus thagus (Pelecaniformes: Pelecanidae)
- Authors: Will S. Jeyasingham; Scott A. Taylor, Carlos B. Zavalaga, Alejandro Simeone, Vicki L. Friesen
Pages: no - no
Abstract: Recent research has shown that tropical seabirds specialized to feed on cold water upwellings exhibit low population genetic differentiation and high gene flow across large geographic distances. This pattern is opposite to the general pattern of differentiation reported for tropical seabirds, and led us to hypothesize that specialization to cold‐water upwellings facilitates gene flow between colonies. As a test of this hypothesis we characterized population differentiation and gene flow across the range of the Peruvian pelican Pelecanus thagus, an upwelling specialist endemic to the Humboldt Current, using an 838 base pair segment of the mitochondrial control region and seven microsatellite loci. In support of our hypothesis we report genetic panmixia across the geographic range of this species and inferred high gene flow between colonies. The high dispersal propensity of upwelling specialist seabirds (adults and/or juveniles) may reduce loss of genetic diversity during population declines, and increase the ability of these species to colonize new islands.
PubDate: 2013-01-30T09:25:31.958564-05:
DOI: 10.1111/j.1600-048X.2012.00004.x
- Authors: Will S. Jeyasingham; Scott A. Taylor, Carlos B. Zavalaga, Alejandro Simeone, Vicki L. Friesen
- Nestling sex predicts susceptibility to parasitism and influences parasite population size within avian broods
- Authors: Erin L. O’Brien; Russell D. Dawson
Pages: no - no
Abstract: Vertebrate hosts differ in their level of parasite susceptibility and infestation. In avian broods, variation in susceptibility of nestlings to ectoparasites may be associated with non‐uniform distributions of parasites among brood mates, with parasites concentrating feeding on the most vulnerable hosts. The presence of a highly susceptible nestling in a brood can benefit the remaining young by reducing the parasite pressure they experience; however, from a parasite’s perspective, broods with fewer susceptible hosts may provide effectively fewer resources than broods of the same size containing a greater abundance of susceptible hosts, and this could limit the number of parasites that a host brood can sustain. To test whether variation in number of susceptible hosts affects the number of parasites in bird nests, we first examined the role of host sex and induced immunity (via methionine supplementation) on susceptibility of mountain bluebirds Sialia currucoides to parasitism by blow flies Protocalliphora spp. We then assessed the effect of variation in number of susceptible hosts on the number of parasites inhabiting the nest. Only females showed a benefit of methionine supplementation, gaining mass more rapidly following supplementation compared to males. This suggests that females are more susceptible to parasites in this system; this was further supported by parasite feeding trials, in which parasites extracted larger blood meals from female than male hosts. Finally, the abundance of parasites in nests was predicted by brood sex ratio: broods containing more female young harboured more parasites. Hence, within‐brood variation in host susceptibility to parasites can not only influence the costs of parasitism for individual nestlings, but may also have consequences for the size of parasite populations within nests. If patterns of maternal investment affect the abundance of nest‐dwelling parasites, these interactions may be important for understanding fitness consequences of maternal resource allocation in many vertebrate hosts.
PubDate: 2013-01-23T09:35:29.432472-05:
DOI: 10.1111/j.1600-048X.2012.05802.x
- Authors: Erin L. O’Brien; Russell D. Dawson
- Genetic structure and phylogeography of a European flagship species, the white‐tailed sea eagle Haliaeetus albicilla
- Authors: Tobias Langguth; Ann‐Christin Honnen, Frank Hailer, Tadeusz Mizera, Stefan Skoric, Ülo Väli, Frank E. Zachos
Pages: no - no
Abstract: We analysed 120 white‐tailed sea eagles Haliaeetus albicilla from eastern (Poland and Estonia) and southeastern (Serbian Danube population) Europe for genetic variability and structuring at the mitochondrial control region and seven nuclear microsatellite loci. We combined this new dataset with sequence and genotype data from previous analyses covering Greenland and Eurasia (total sample sizes of 420 and 186 individuals for mtDNA and microsatellites, respectively) to address the following questions: 1) does the large eastern population in Europe add significantly to the species‘ overall genetic diversity' 2) Do the new sequence data match the clinal distribution pattern (west to east) of the two major mtDNA lineages' 3) Does the preliminary hypothesis of two nuclear genetic clusters recently found in this species hold for the whole of Europe, and do these clusters show a geographic pattern' Our results confirmed Europe as a stronghold of genetic diversity in white‐tailed sea eagles, and the east of the continent contributed disproportionately to this, the reason being the admixture of eagles with different genetic background. As hypothesised, both mitochondrial lineages were recovered also in eastern Europe, but the globally more eastern lineage was dominant. The presence of two microsatellite clusters was also confirmed, and these groups, too, show a non‐random geographic distribution, with, except for Poland, a high proportion of ‘eastern‐type’ eagles in the populations of east–central and eastern Europe.
PubDate: 2012-12-17T05:55:21.946599-05:
DOI: 10.1111/j.1600-048X.2012.00075.x
- Authors: Tobias Langguth; Ann‐Christin Honnen, Frank Hailer, Tadeusz Mizera, Stefan Skoric, Ülo Väli, Frank E. Zachos
- Co‐infections by malaria parasites decrease feather growth but not feather quality in house martin
- Abstract: During moult, stressors such as malaria and related haemosporidian parasites (e.g. Plasmodium and Haemoproteus) could affect the growth rate and quality of feathers, which in turn may compromise future reproduction and survival. Recent advances in molecular methods to study parasites have revealed that co‐infections with multiple parasites are frequent in bird–malaria parasite systems. However, there is no study of the consequences of co‐infections on the moult of birds. In house martins Delichon urbica captured and studied at a breeding site in Europe during 11 yr, we measured the quality and the growth rate of tail feathers moulted in the African winter quarters in parallel with the infection status of blood parasites that are also transmitted on the wintering ground. Here we tested if the infection with two haemosporidian parasite lineages has more negative effects than a single lineage infection. We found that birds with haemosporidian infection had lower body condition. We also found that birds co‐infected with two haemosporidian lineages had the lowest inferred growth rate of their tail feathers as compared with uninfected and single infected individuals, but co‐infections had no effect on feather quality. In addition, feather quality was negatively correlated with feather growth rate, suggesting that these two traits are traded‐off against each other. We encourage the study of haemosporidian parasite infection as potential mechanism driving this trade‐off in wild populations of birds.
- Abstract: During moult, stressors such as malaria and related haemosporidian parasites (e.g. Plasmodium and Haemoproteus) could affect the growth rate and quality of feathers, which in turn may compromise future reproduction and survival. Recent advances in molecular methods to study parasites have revealed that co‐infections with multiple parasites are frequent in bird–malaria parasite systems. However, there is no study of the consequences of co‐infections on the moult of birds. In house martins Delichon urbica captured and studied at a breeding site in Europe during 11 yr, we measured the quality and the growth rate of tail feathers moulted in the African winter quarters in parallel with the infection status of blood parasites that are also transmitted on the wintering ground. Here we tested if the infection with two haemosporidian parasite lineages has more negative effects than a single lineage infection. We found that birds with haemosporidian infection had lower body condition. We also found that birds co‐infected with two haemosporidian lineages had the lowest inferred growth rate of their tail feathers as compared with uninfected and single infected individuals, but co‐infections had no effect on feather quality. In addition, feather quality was negatively correlated with feather growth rate, suggesting that these two traits are traded‐off against each other. We encourage the study of haemosporidian parasite infection as potential mechanism driving this trade‐off in wild populations of birds.
- Litter and seed burying alter food availability and foraging efficiency of granivorous birds in the Monte desert
- Abstract: We assessed experimentally if the main granivorous bird species that feed on the ground in the central Monte desert are able to detect and consume seeds buried in the soil or trapped within litter. Understanding seed vulnerability to birds allows 1) a better understanding of how seed abundance translates into seed availability, a necessary step to assess seed limitation scenarios, and 2) whether birds alter the distribution of soil seeds through their consumption. Rufous‐collared sparrows found and consumed high proportions of buried seeds, though less seeds were eaten at increasing depths. In contrast, many‐colored chaco‐finches, common diuca‐finches and cinnamon warbling‐finches did not find buried seeds. All bird species fed on every substrate offered but, as a whole, birds reduced by 50% their seed consumption in Prosopis litter, and by 30% in Larrea litter, compared to consumption in bare soil. This effect was less notable for rufous‐collared sparrows, whose ‘double scratch’ foraging method would contribute to its great diet breath and abundance in the Monte desert. As birds do not reach a fraction of seeds buried and trapped by litter, seeds readily available for them may be scarcer than previously estimated through soil seed bank studies. Furthermore, since the four bird species detect and consume seeds from littered microhabitats, seed consumption by them surely affects the seasonal dynamics of the soil seed bank in all microhabitat types of the Monte desert.
- Abstract: We assessed experimentally if the main granivorous bird species that feed on the ground in the central Monte desert are able to detect and consume seeds buried in the soil or trapped within litter. Understanding seed vulnerability to birds allows 1) a better understanding of how seed abundance translates into seed availability, a necessary step to assess seed limitation scenarios, and 2) whether birds alter the distribution of soil seeds through their consumption. Rufous‐collared sparrows found and consumed high proportions of buried seeds, though less seeds were eaten at increasing depths. In contrast, many‐colored chaco‐finches, common diuca‐finches and cinnamon warbling‐finches did not find buried seeds. All bird species fed on every substrate offered but, as a whole, birds reduced by 50% their seed consumption in Prosopis litter, and by 30% in Larrea litter, compared to consumption in bare soil. This effect was less notable for rufous‐collared sparrows, whose ‘double scratch’ foraging method would contribute to its great diet breath and abundance in the Monte desert. As birds do not reach a fraction of seeds buried and trapped by litter, seeds readily available for them may be scarcer than previously estimated through soil seed bank studies. Furthermore, since the four bird species detect and consume seeds from littered microhabitats, seed consumption by them surely affects the seasonal dynamics of the soil seed bank in all microhabitat types of the Monte desert.
- Resource allocation between growth and endothermy allows rapid nestling development at low feeding rates in a species under high nest predation
- Abstract: Nestling development is among the most energy‐demanding periods of a bird’s lifetime and altricial species require extensive parental energy investment in the form of feeding and heating. In the present study I analyze the relation and trade‐offs between nestling growth, development of thermoregulation and feeding rate in blackcap Sylvia atricapilla, a species suffering from high nest predation. Nestlings were characterized by rapid growth but they achieved only 80% of adult mass prior to fledging. Body mass showed highest relative growth rate before nestlings achieved homeothermy. The onset of endothermy, indicated in day 7, coincided with 90% of nestling fledgling weight, indicating that the two processes are separated in time. A strong negative correlation between feeding rate and growth rate demonstrates that blackcap nestlings develop their bodies under relatively low feeding rates and more feeding is needed for maintenance of body temperature than for body growth. The study indicates high cost of endothermy for parents – endothermic nestlings received over 100% more feedings than ectothermic ones. The findings are discussed in the light of adaptation of the species to high predation risk.
- Abstract: Nestling development is among the most energy‐demanding periods of a bird’s lifetime and altricial species require extensive parental energy investment in the form of feeding and heating. In the present study I analyze the relation and trade‐offs between nestling growth, development of thermoregulation and feeding rate in blackcap Sylvia atricapilla, a species suffering from high nest predation. Nestlings were characterized by rapid growth but they achieved only 80% of adult mass prior to fledging. Body mass showed highest relative growth rate before nestlings achieved homeothermy. The onset of endothermy, indicated in day 7, coincided with 90% of nestling fledgling weight, indicating that the two processes are separated in time. A strong negative correlation between feeding rate and growth rate demonstrates that blackcap nestlings develop their bodies under relatively low feeding rates and more feeding is needed for maintenance of body temperature than for body growth. The study indicates high cost of endothermy for parents – endothermic nestlings received over 100% more feedings than ectothermic ones. The findings are discussed in the light of adaptation of the species to high predation risk.
- The vigilance components of begging and sibling competition
- Abstract: The conflict between siblings over how parental resources are divided has promoted the evolution of specific behaviour to outcompete each other. Young animals look out for parents’ arrival in order to start begging as quickly as possible, since a rapid begging reaction increases the likelihood of being fed before nestmates. If the young can physically intercept the parents, selection might be operating on the offspring ability to monitor parent arrival (vigilance towards parents) and any sudden modifications in siblings’ behaviour (vigilance towards siblings). To investigate the adaptive value of nestling vigilance in the context of family interactions, we recorded which direction barn owl Tyto alba siblings were facing in 89 two‐chick broods before the first parental feeding visit of the night. Nestlings were more vigilant towards nest entrance than expected by chance suggesting that vigilance towards parents is an important component of sibling competition. When positioned near the nest‐box entrance where parents predictably deliver food, the younger individual (i.e. junior) looked more towards the entrance than its older sibling. Thus, when the likelihood of obtaining a food item is relatively high, juniors are more vigilant than seniors to detect the incoming parent. When positioned at the back of the nest, the senior looked relatively more frequently towards its sibling than the junior did in the same situation. This suggests that when the likelihood of obtaining a food item is relatively low, seniors are more vigilant than juniors to observe their sibling. Because vigilance was not related to hunger level and prey obtaining, we propose the hypothesis that vigilance towards parents and siblings only indirectly influences the outcome of sibling competition.
- Abstract: The conflict between siblings over how parental resources are divided has promoted the evolution of specific behaviour to outcompete each other. Young animals look out for parents’ arrival in order to start begging as quickly as possible, since a rapid begging reaction increases the likelihood of being fed before nestmates. If the young can physically intercept the parents, selection might be operating on the offspring ability to monitor parent arrival (vigilance towards parents) and any sudden modifications in siblings’ behaviour (vigilance towards siblings). To investigate the adaptive value of nestling vigilance in the context of family interactions, we recorded which direction barn owl Tyto alba siblings were facing in 89 two‐chick broods before the first parental feeding visit of the night. Nestlings were more vigilant towards nest entrance than expected by chance suggesting that vigilance towards parents is an important component of sibling competition. When positioned near the nest‐box entrance where parents predictably deliver food, the younger individual (i.e. junior) looked more towards the entrance than its older sibling. Thus, when the likelihood of obtaining a food item is relatively high, juniors are more vigilant than seniors to detect the incoming parent. When positioned at the back of the nest, the senior looked relatively more frequently towards its sibling than the junior did in the same situation. This suggests that when the likelihood of obtaining a food item is relatively low, seniors are more vigilant than juniors to observe their sibling. Because vigilance was not related to hunger level and prey obtaining, we propose the hypothesis that vigilance towards parents and siblings only indirectly influences the outcome of sibling competition.
- Bird pollinators differ in their tolerance of a nectar alkaloid
- Abstract: Although the function of nectar is to attract and reward pollinators, secondary metabolites produced by plants as anti‐herbivore defences are frequently present in floral nectars. Greater understanding is needed of the effects of secondary metabolites in nectar on the foraging behaviour and performance of pollinators, and on plant–pollinator interactions. We investigated how nectar‐feeding birds, both specialist (white‐bellied sunbirds Cinnyris talatala) and generalist (dark‐capped bulbuls Pycnonotus tricolor and Cape white‐eyes Zosterops virens), respond to artificial nectar containing the alkaloid nicotine, present in nectar of Nicotiana species. Preference tests were carried out with a range of nicotine concentrations (0.1–300 μM) in two sucrose concentrations (0.25 and 1 M), and for bulbuls also in two sugars (sucrose and hexose). In addition, we measured short‐term feeding patterns in white‐bellied sunbirds that were offered nicotine (0–50 μM) in 0.63 M sucrose. Both nicotine and sugar concentrations influenced the response of bird pollinators to nicotine. The birds showed dose‐dependent responses to nicotine; and their tolerance of high nicotine concentrations was reduced on the dilute 0.25 M sucrose diet, on which they increased consumption to maintain energy intake. White‐bellied sunbirds decreased both feeding frequency and feeding duration as the nicotine concentration in artificial nectar increased. Of the three species, bulbuls showed the highest tolerance for nicotine, and sugar type (sucrose or hexose) had no effect. The indifference of bulbuls to nicotine may be related to their primarily frugivorous diet. However, the response of white‐eyes to nicotine in the dilute sucrose solution was very similar to that of sunbirds, even though white‐eyes are generalist nectar‐feeders. Additional testing of other avian nectarivores and different secondary metabolites is required to further elucidate whether generalist bird pollinators, which utilise dilute nectars in which secondary metabolites have stronger deterrent effects, are more tolerant of ‘toxic’ nectar.
- Abstract: Although the function of nectar is to attract and reward pollinators, secondary metabolites produced by plants as anti‐herbivore defences are frequently present in floral nectars. Greater understanding is needed of the effects of secondary metabolites in nectar on the foraging behaviour and performance of pollinators, and on plant–pollinator interactions. We investigated how nectar‐feeding birds, both specialist (white‐bellied sunbirds Cinnyris talatala) and generalist (dark‐capped bulbuls Pycnonotus tricolor and Cape white‐eyes Zosterops virens), respond to artificial nectar containing the alkaloid nicotine, present in nectar of Nicotiana species. Preference tests were carried out with a range of nicotine concentrations (0.1–300 μM) in two sucrose concentrations (0.25 and 1 M), and for bulbuls also in two sugars (sucrose and hexose). In addition, we measured short‐term feeding patterns in white‐bellied sunbirds that were offered nicotine (0–50 μM) in 0.63 M sucrose. Both nicotine and sugar concentrations influenced the response of bird pollinators to nicotine. The birds showed dose‐dependent responses to nicotine; and their tolerance of high nicotine concentrations was reduced on the dilute 0.25 M sucrose diet, on which they increased consumption to maintain energy intake. White‐bellied sunbirds decreased both feeding frequency and feeding duration as the nicotine concentration in artificial nectar increased. Of the three species, bulbuls showed the highest tolerance for nicotine, and sugar type (sucrose or hexose) had no effect. The indifference of bulbuls to nicotine may be related to their primarily frugivorous diet. However, the response of white‐eyes to nicotine in the dilute sucrose solution was very similar to that of sunbirds, even though white‐eyes are generalist nectar‐feeders. Additional testing of other avian nectarivores and different secondary metabolites is required to further elucidate whether generalist bird pollinators, which utilise dilute nectars in which secondary metabolites have stronger deterrent effects, are more tolerant of ‘toxic’ nectar.
- The epidemiology underlying age‐related avian malaria infection in a long‐lived host: the mute swan Cygnus olor
- Abstract: Quantifying the factors that predict parasite outbreak and persistence is a major challenge for both applied and fundamental biology. Key to understanding parasite prevalence and disease outbreaks is determining at what age individuals show signs of infection, and whether or not they recover. Age‐dependent patterns of the infection of a host population by parasites can indicate among‐individual heterogeneities in their susceptibility to, or rate of recovery from, parasite infections. Here, we present a cross‐sectional study of avian malaria in a long‐lived bird species, the mute swan Cygnus olor, examining age‐related patterns of parasite prevalence and modelling patterns of infection and recovery. One‐hundred and fifteen swans, ranging from one to nineteen years old, were screened for infection with Plasmodium, Haemoproteus and Leucocytozoon parasites. Infections with three cytochrome‐b lineages of Haemoproteus were found (pooled prevalence 67%), namely WW1 (26%), which is common in passerine birds, and two new lineages closely related to WW1: MUTSW1 (25%) and MUTSW2 (16%). We found evidence for age‐related infection in one lineage, MUTSW1. Catalytic models examining patterns of infection and recovery in the population suggested that infections in this population were not life‐long – recovery of individuals was included in the best fitting models. These findings support the results of recent studies that suggest hosts can clear infections, although patterns of infection‐related mortality in older birds remain to be studied in more detail.
- Abstract: Quantifying the factors that predict parasite outbreak and persistence is a major challenge for both applied and fundamental biology. Key to understanding parasite prevalence and disease outbreaks is determining at what age individuals show signs of infection, and whether or not they recover. Age‐dependent patterns of the infection of a host population by parasites can indicate among‐individual heterogeneities in their susceptibility to, or rate of recovery from, parasite infections. Here, we present a cross‐sectional study of avian malaria in a long‐lived bird species, the mute swan Cygnus olor, examining age‐related patterns of parasite prevalence and modelling patterns of infection and recovery. One‐hundred and fifteen swans, ranging from one to nineteen years old, were screened for infection with Plasmodium, Haemoproteus and Leucocytozoon parasites. Infections with three cytochrome‐b lineages of Haemoproteus were found (pooled prevalence 67%), namely WW1 (26%), which is common in passerine birds, and two new lineages closely related to WW1: MUTSW1 (25%) and MUTSW2 (16%). We found evidence for age‐related infection in one lineage, MUTSW1. Catalytic models examining patterns of infection and recovery in the population suggested that infections in this population were not life‐long – recovery of individuals was included in the best fitting models. These findings support the results of recent studies that suggest hosts can clear infections, although patterns of infection‐related mortality in older birds remain to be studied in more detail.
- Alula size signals male condition and predicts reproductive performance in an Arctic‐breeding passerine
- Abstract: While studies of achromatic plumage signaling are scarce relative to chromatic ornaments, achromatic ornaments have the potential to act as an efficient form of visual communication due to the highly conspicuous contrast between black and white body regions. Recently, achromatic plumage reflectance has been shown to indicate condition, yet the condition‐dependence of achromatic patch size remains unstudied. Here we show the first evidence that alula size, an achromatic plumage patch, has the potential to signal a male’s condition and predict reproductive performance. In Arctic‐breeding snow buntings Plectrophenax nivalis, the size of the alula simultaneously predicted pre‐breeding physiological health and the number of offspring produced, through an intermediate variable (lay date). Snow buntings appear to pair assortatively; males and females arriving earlier pair together, and changes in body condition over the breeding season are positively related within pairs. We suggest that simple achromatic plumage patches, like alula size, have the potential to act as condition‐dependent signals. Consequently, females may benefit from assessing these signals to reliably evaluate a male’s condition and reproductive potential as a means of maximizing their reproductive success.
- Abstract: While studies of achromatic plumage signaling are scarce relative to chromatic ornaments, achromatic ornaments have the potential to act as an efficient form of visual communication due to the highly conspicuous contrast between black and white body regions. Recently, achromatic plumage reflectance has been shown to indicate condition, yet the condition‐dependence of achromatic patch size remains unstudied. Here we show the first evidence that alula size, an achromatic plumage patch, has the potential to signal a male’s condition and predict reproductive performance. In Arctic‐breeding snow buntings Plectrophenax nivalis, the size of the alula simultaneously predicted pre‐breeding physiological health and the number of offspring produced, through an intermediate variable (lay date). Snow buntings appear to pair assortatively; males and females arriving earlier pair together, and changes in body condition over the breeding season are positively related within pairs. We suggest that simple achromatic plumage patches, like alula size, have the potential to act as condition‐dependent signals. Consequently, females may benefit from assessing these signals to reliably evaluate a male’s condition and reproductive potential as a means of maximizing their reproductive success.
- Chronic stress in infancy fails to affect body size and immune response of adult female blue‐footed boobies or their offspring
- Abstract: Experiments on birds, fish and mammals have shown that adverse conditions during infancy can produce diverse long‐term and delayed deficits during adulthood, prejudicing both the individual and its offspring. Natural selection should prepare animals to cope with adversity of the type, magnitude and timing that commonly occur in their natural habitat, but very little is known about such evolved developmental buffering against natural ‘poor starts’ in life. In two‐chick broods of the blue‐footed booby Sula nebouxii, the junior (younger) chick usually experiences aggressive subordination, reduced nutrition and growth and elevated circulating corticosterone. To test whether this poor start produces long‐term, delayed or intergenerational deficits in body size, body condition or cell‐mediated immune response, we measured 3–8 yr old female breeders banded as chicks, and their infant offspring. Results failed to support our predictions. Compared to former seniors and former singletons (solitary nestlings), former juniors showed no deficit in cell‐mediated immune response at any age. They showed an 8.04% deficit in body condition at age 4–6 yr but this deficit disappeared completely by age 7–8 yr. Furthermore, their offspring showed no deficits in body size, body condition or immune response. Junior chicks are affected by their poor start, but their developmental resilience, also confirmed by studies of post‐fledging survivorship, recruitment, natal dispersal, aggressive nest defense and reproduction, is evidence of evolved developmental buffering against predictable adversity during infancy.
- Abstract: Experiments on birds, fish and mammals have shown that adverse conditions during infancy can produce diverse long‐term and delayed deficits during adulthood, prejudicing both the individual and its offspring. Natural selection should prepare animals to cope with adversity of the type, magnitude and timing that commonly occur in their natural habitat, but very little is known about such evolved developmental buffering against natural ‘poor starts’ in life. In two‐chick broods of the blue‐footed booby Sula nebouxii, the junior (younger) chick usually experiences aggressive subordination, reduced nutrition and growth and elevated circulating corticosterone. To test whether this poor start produces long‐term, delayed or intergenerational deficits in body size, body condition or cell‐mediated immune response, we measured 3–8 yr old female breeders banded as chicks, and their infant offspring. Results failed to support our predictions. Compared to former seniors and former singletons (solitary nestlings), former juniors showed no deficit in cell‐mediated immune response at any age. They showed an 8.04% deficit in body condition at age 4–6 yr but this deficit disappeared completely by age 7–8 yr. Furthermore, their offspring showed no deficits in body size, body condition or immune response. Junior chicks are affected by their poor start, but their developmental resilience, also confirmed by studies of post‐fledging survivorship, recruitment, natal dispersal, aggressive nest defense and reproduction, is evidence of evolved developmental buffering against predictable adversity during infancy.
- Chick growth and survival in northern lapwings Vanellus vanellus indicate that secondary females do the best of a bad job
- Abstract: The polygyny threshold model predicts that monogamous and secondary females on average settle at the same time and have similar reproductive success. This is not generally found. Incorporating varying female competitive strength into the model, changes the predictions to state that secondary females should breed later and show a reduced success compared to that of monogamous and primary females. We examined if this was the case by investigating growth and survival in chicks of northern lapwings Vanellus vanellus from mothers of monogamous, primary and secondary mating status. Chicks where monitored from hatching to the age of 15–18 d. Growth and survival in secondary chicks was lower than in monogamous and primary chicks. Primary chicks survived significantly better than secondary chicks. Survival of monogamous chicks was comparable to primary chicks and close to significantly higher than in secondary chicks (p = 0.086). Among surviving chicks, daily weight gain in monogamous chicks was significantly higher than in secondary chicks. Growth rates of primary chicks were comparable to monogamous chicks and tended to be higher than in secondary chicks (p = 0.11). Monogamous and primary females both bred significantly earlier than secondary females, and chick survival and body‐mass growth decreased significantly with hatching date. Given the premium on early breeding in lapwings, secondary females appeared to do the best of a bad job, and their later onset of breeding could have been caused by poorer condition and/or lower breeding experience. Additional costs might also have accrued from sharing breeding resources with primary females that presumably were stronger competitors.
- Abstract: The polygyny threshold model predicts that monogamous and secondary females on average settle at the same time and have similar reproductive success. This is not generally found. Incorporating varying female competitive strength into the model, changes the predictions to state that secondary females should breed later and show a reduced success compared to that of monogamous and primary females. We examined if this was the case by investigating growth and survival in chicks of northern lapwings Vanellus vanellus from mothers of monogamous, primary and secondary mating status. Chicks where monitored from hatching to the age of 15–18 d. Growth and survival in secondary chicks was lower than in monogamous and primary chicks. Primary chicks survived significantly better than secondary chicks. Survival of monogamous chicks was comparable to primary chicks and close to significantly higher than in secondary chicks (p = 0.086). Among surviving chicks, daily weight gain in monogamous chicks was significantly higher than in secondary chicks. Growth rates of primary chicks were comparable to monogamous chicks and tended to be higher than in secondary chicks (p = 0.11). Monogamous and primary females both bred significantly earlier than secondary females, and chick survival and body‐mass growth decreased significantly with hatching date. Given the premium on early breeding in lapwings, secondary females appeared to do the best of a bad job, and their later onset of breeding could have been caused by poorer condition and/or lower breeding experience. Additional costs might also have accrued from sharing breeding resources with primary females that presumably were stronger competitors.
- Metabolic response to changes in temperature in northern wheatears from an arctic and a temperate populations
- Abstract: Until recently it had been widely accepted that birds are energetically adapted to the latitude they inhabit, having an increased basal metabolic rate (BMR) at higher latitudes. Latterly, this general view has been questioned and the influence of phenotypic flexibility, due to factors such as habitat, life‐history or acclimatization has received increased attention. In particular, focus has been directed towards comparing species from arid and mesic habitats, but less attention has been given to species which breed in cold climates. We chose to study northern wheatears Oenanthe oenanthe from two populations at different latitudes (southern Norway, Iceland), but with similar life‐histories and habitat requirements throughout the year, in a common‐garden experiment. In order to assess true latitudinal trends in metabolic rate, we estimated the nocturnal resting metabolic rate (RMR) of northern wheatears from southern Norway and Iceland at different temperatures from 0° to 30°C. We found that Norwegian birds had overall lower metabolic rates than Icelandic birds, which were also slightly larger. This difference was not observed at 0°C, which might indicate that Icelandic birds might rely on better feather insulation reducing metabolic costs at very low temperatures. At temperatures above 10°C birds of both populations had constant metabolic values, indicating that their thermoneutral range almost completely covered the temperatures experienced during the breeding period. This study shows that the northern wheatear, which is one of only a few insectivorous long‐distance migratory songbirds occurring at such high latitudes, has evolved metabolic adaptations to life at cold temperatures which are endogenously determined.
- Abstract: Until recently it had been widely accepted that birds are energetically adapted to the latitude they inhabit, having an increased basal metabolic rate (BMR) at higher latitudes. Latterly, this general view has been questioned and the influence of phenotypic flexibility, due to factors such as habitat, life‐history or acclimatization has received increased attention. In particular, focus has been directed towards comparing species from arid and mesic habitats, but less attention has been given to species which breed in cold climates. We chose to study northern wheatears Oenanthe oenanthe from two populations at different latitudes (southern Norway, Iceland), but with similar life‐histories and habitat requirements throughout the year, in a common‐garden experiment. In order to assess true latitudinal trends in metabolic rate, we estimated the nocturnal resting metabolic rate (RMR) of northern wheatears from southern Norway and Iceland at different temperatures from 0° to 30°C. We found that Norwegian birds had overall lower metabolic rates than Icelandic birds, which were also slightly larger. This difference was not observed at 0°C, which might indicate that Icelandic birds might rely on better feather insulation reducing metabolic costs at very low temperatures. At temperatures above 10°C birds of both populations had constant metabolic values, indicating that their thermoneutral range almost completely covered the temperatures experienced during the breeding period. This study shows that the northern wheatear, which is one of only a few insectivorous long‐distance migratory songbirds occurring at such high latitudes, has evolved metabolic adaptations to life at cold temperatures which are endogenously determined.
- Satellite telemetry reveals long‐distance migration in the Asian great bustard Otis tarda dybowskii
- Abstract: The range of the great bustard stretches 10 000 km across Eurasia, one of the largest ranges of any threatened species. While movement patterns of the western subspecies of great bustard are relatively well‐understood, this is the first research to monitor the movements of the more endangered Asian subspecies of great bustard through telemetry and to link a breeding population of Asian great bustards to their wintering grounds. Using Argos/GPS platform transmitter terminals, we identified the annual movement patterns of three female great bustards captured at their breeding sites in northern Mongolia. The 4000 km round‐trip migration we have recorded terminated at wintering grounds in Shaanxi, China. This route is twice as long as has previously been reported for great bustards, which are among the heaviest flying birds. The journey was accomplished in approximately two months each way, at ground velocities of 48–98 km h−1, and incorporated multiple and variable stopover sites. On their wintering grounds these birds moved itinerantly across relatively large home ranges. Our findings confirm that migratory behavior in this species varies longitudinally. This variation may be attributable to longitudinal gradients in seasonality and severity of winter across Eurasia. The distance and duration of the migratory route taken by great bustards breeding in Mongolia, the crossing of an international border, the incorporation of many stopovers, and the use of a large wintering territory present challenges to the conservation of the Asian subspecies of great bustard in this rapidly changing part of the world.
- Abstract: The range of the great bustard stretches 10 000 km across Eurasia, one of the largest ranges of any threatened species. While movement patterns of the western subspecies of great bustard are relatively well‐understood, this is the first research to monitor the movements of the more endangered Asian subspecies of great bustard through telemetry and to link a breeding population of Asian great bustards to their wintering grounds. Using Argos/GPS platform transmitter terminals, we identified the annual movement patterns of three female great bustards captured at their breeding sites in northern Mongolia. The 4000 km round‐trip migration we have recorded terminated at wintering grounds in Shaanxi, China. This route is twice as long as has previously been reported for great bustards, which are among the heaviest flying birds. The journey was accomplished in approximately two months each way, at ground velocities of 48–98 km h−1, and incorporated multiple and variable stopover sites. On their wintering grounds these birds moved itinerantly across relatively large home ranges. Our findings confirm that migratory behavior in this species varies longitudinally. This variation may be attributable to longitudinal gradients in seasonality and severity of winter across Eurasia. The distance and duration of the migratory route taken by great bustards breeding in Mongolia, the crossing of an international border, the incorporation of many stopovers, and the use of a large wintering territory present challenges to the conservation of the Asian subspecies of great bustard in this rapidly changing part of the world.
- High rates of conspecific brood parasitism revealed by microsatellite analysis in a diving duck, the common pochard Aythya ferina
- Abstract: Conspecific brood parasitism (CBP) is a reproductive tactic whereby a parasitic female lays its eggs into the nests of other conspecific females. Genetic‐based data on the occurrence of CBP in birds, however, is still relatively scarce. We analysed prevalence of CBP in a ground‐nesting diving duck, the common pochard Aythya ferina, using a set of 17 microsatellites. Compared to related species, our population showed a relatively high level of CBP, with 39% of genotyped pochard eggs laid parasitically and 89% of nests containing ≥ 1 parasitic egg. In addition, we observed relatively high rates of interspecific brood parasitism (13% of eggs), caused predominantly by mallard Anas plathyrhynchos and tufted duck Aythya fuligula. CBP eggs had decreased hatching success compared to host eggs, with 65% of CBP and 95% of non‐CBP genotyped eggs hatching successfully. Our data suggest that this was probably due to improper timing of parasitic egglaying, which compromised synchronised hatching of CBP and host‐eggs. Despite high rates of CBP in our pochard popu lation, fitness costs associated with this reproductive tactic appear to be low for host females since neither clutch size nor host‐egg hatching probability were reduced due to CBP.
- Abstract: Conspecific brood parasitism (CBP) is a reproductive tactic whereby a parasitic female lays its eggs into the nests of other conspecific females. Genetic‐based data on the occurrence of CBP in birds, however, is still relatively scarce. We analysed prevalence of CBP in a ground‐nesting diving duck, the common pochard Aythya ferina, using a set of 17 microsatellites. Compared to related species, our population showed a relatively high level of CBP, with 39% of genotyped pochard eggs laid parasitically and 89% of nests containing ≥ 1 parasitic egg. In addition, we observed relatively high rates of interspecific brood parasitism (13% of eggs), caused predominantly by mallard Anas plathyrhynchos and tufted duck Aythya fuligula. CBP eggs had decreased hatching success compared to host eggs, with 65% of CBP and 95% of non‐CBP genotyped eggs hatching successfully. Our data suggest that this was probably due to improper timing of parasitic egglaying, which compromised synchronised hatching of CBP and host‐eggs. Despite high rates of CBP in our pochard popu lation, fitness costs associated with this reproductive tactic appear to be low for host females since neither clutch size nor host‐egg hatching probability were reduced due to CBP.
- Host selection in parasitic birds: are open‐cup nesting insectivorous passerines always suitable cuckoo hosts'
- Abstract: How do potential hosts escape detrimental interactions with brood parasites' Current consensus is that hole‐nesting and granivorous birds avoid brood parasites, like common cuckoos Cuculus canorus, by their inaccessible nest‐sites and food unsuitable for parasites, respectively. Any open‐nesting insectivorous hosts are believed to remain open to brood parasite exploitation which leads to the evolution of costly host defences like egg or chick discrimination. In contrast to this coevolutionary scenario, we show for the first time that a previously not studied but seemingly suitable host species escapes brood parasites. The Asian verditer flycatcher Eumyias thalassinus, feed newly hatched chicks entirely with beetles and grasshoppers. These are poor quality and hard to digest diet items that are rarely fed to own or cuckoo chicks by regular hosts. Indeed, chick cross‐fostering experiments showed that these food items remained undigested by either cuckoos or other sympatric passerines causing them to die quickly. Egg discrimination experiments showed that the flycatcher accepts any foreign eggs. Although most but not all other potential explanations can be safely excluded at present, the most parsimonious historical explanation for these patterns is that the flycatcher exploits a trophic niche that no other sympatric bird can exploit, and that any cuckoo lineages that switch from their original hosts to the flycatcher have no possibilities for establishing viable populations. Thus, the current classification of host suitability based on diet composition may need revision, raising an important cautionary tale for comparative studies and the interpretation of apparent host rejection of parasitic chicks.
- Abstract: How do potential hosts escape detrimental interactions with brood parasites' Current consensus is that hole‐nesting and granivorous birds avoid brood parasites, like common cuckoos Cuculus canorus, by their inaccessible nest‐sites and food unsuitable for parasites, respectively. Any open‐nesting insectivorous hosts are believed to remain open to brood parasite exploitation which leads to the evolution of costly host defences like egg or chick discrimination. In contrast to this coevolutionary scenario, we show for the first time that a previously not studied but seemingly suitable host species escapes brood parasites. The Asian verditer flycatcher Eumyias thalassinus, feed newly hatched chicks entirely with beetles and grasshoppers. These are poor quality and hard to digest diet items that are rarely fed to own or cuckoo chicks by regular hosts. Indeed, chick cross‐fostering experiments showed that these food items remained undigested by either cuckoos or other sympatric passerines causing them to die quickly. Egg discrimination experiments showed that the flycatcher accepts any foreign eggs. Although most but not all other potential explanations can be safely excluded at present, the most parsimonious historical explanation for these patterns is that the flycatcher exploits a trophic niche that no other sympatric bird can exploit, and that any cuckoo lineages that switch from their original hosts to the flycatcher have no possibilities for establishing viable populations. Thus, the current classification of host suitability based on diet composition may need revision, raising an important cautionary tale for comparative studies and the interpretation of apparent host rejection of parasitic chicks.
- Is there variation in the response to contact call playbacks across the hybrid zone of the parrot Platycercus elegans'
- Abstract: Learned vocal signals could be important in the formation of prezygotic isolation between two hybridising taxa. This study examined whether vocal variation in the parrot Platycercus elegans facilitates the separation of individuals from two subspecies, P. e. elegans (CR) and P. e. flaveolus (YR). CR and YR have very different plumage coloration, respectively deep crimson and pale yellow, but hybridise where they meet creating an intermediate population (WS). In a factorial design playback experiment, we conducted 108 playback trials on three focal populations (YR, WS, CR), in and around this area of hybridisation, to test if they respond differently to contact calls from their own or another population. We also analysed whether differences in acoustic variables of the stimulus calls predicted the response to the call. We did not find any indication that individuals from the three focal populations responded differently to calls sampled from their own or another subspecies. We did find an effect of two of the five acoustic variables that we used to describe and classify contact calls from the three source populations. Specifically, duration of the stimulus call positively affected the response from individuals from WS and negatively the response from CR, and CR responded more to stimulus calls with a lower peak frequency. Overall, we found no indication that acoustic variation in contact calls on a subspecies level is involved in maintaining plumage colour differences between P. e. elegans and P. e. flaveolus subspecies.
- Abstract: Learned vocal signals could be important in the formation of prezygotic isolation between two hybridising taxa. This study examined whether vocal variation in the parrot Platycercus elegans facilitates the separation of individuals from two subspecies, P. e. elegans (CR) and P. e. flaveolus (YR). CR and YR have very different plumage coloration, respectively deep crimson and pale yellow, but hybridise where they meet creating an intermediate population (WS). In a factorial design playback experiment, we conducted 108 playback trials on three focal populations (YR, WS, CR), in and around this area of hybridisation, to test if they respond differently to contact calls from their own or another population. We also analysed whether differences in acoustic variables of the stimulus calls predicted the response to the call. We did not find any indication that individuals from the three focal populations responded differently to calls sampled from their own or another subspecies. We did find an effect of two of the five acoustic variables that we used to describe and classify contact calls from the three source populations. Specifically, duration of the stimulus call positively affected the response from individuals from WS and negatively the response from CR, and CR responded more to stimulus calls with a lower peak frequency. Overall, we found no indication that acoustic variation in contact calls on a subspecies level is involved in maintaining plumage colour differences between P. e. elegans and P. e. flaveolus subspecies.
- Carry‐over effects of winter habitat vary with age and sex in yellow warblers Setophaga petechia
- Abstract: We use stable isotope data to investigate the role of winter habitat use in altering the breeding phenology of yellow warblers Setophaga petechia. We first confirm that δ13C and δ15N isotopic signatures vary with winter habitat use in this species. We then examine the relationship between winter habitat use, breeding phenology and productivity within four age‐sex‐classes, since life history theory would predict that carry‐over effects should vary with age and gender. The δ13C signatures of yellow warblers using riparian habitats over winter were more depleted than the signatures of those using agricultural or scrub habitat. Individuals on the Pacific coast of Mexico were also more δ15N enriched than those on the southern Gulf of Mexico. δ13C and δ15N signatures were only correlated with earlier clutch initiation and subsequent higher productivity in first‐breeding‐season females. We estimate that shifts in δ13C equivalent to a shift from scrub to riparian winter habitat would be associated with the production of 0.8 more fledglings by yearling females. Pre‐breeding events that influence the timing of breeding could also influence the reproductive performance of older males and females, but we found little evidence that winter habitat use influenced breeding season phenology in these birds.
- Abstract: We use stable isotope data to investigate the role of winter habitat use in altering the breeding phenology of yellow warblers Setophaga petechia. We first confirm that δ13C and δ15N isotopic signatures vary with winter habitat use in this species. We then examine the relationship between winter habitat use, breeding phenology and productivity within four age‐sex‐classes, since life history theory would predict that carry‐over effects should vary with age and gender. The δ13C signatures of yellow warblers using riparian habitats over winter were more depleted than the signatures of those using agricultural or scrub habitat. Individuals on the Pacific coast of Mexico were also more δ15N enriched than those on the southern Gulf of Mexico. δ13C and δ15N signatures were only correlated with earlier clutch initiation and subsequent higher productivity in first‐breeding‐season females. We estimate that shifts in δ13C equivalent to a shift from scrub to riparian winter habitat would be associated with the production of 0.8 more fledglings by yearling females. Pre‐breeding events that influence the timing of breeding could also influence the reproductive performance of older males and females, but we found little evidence that winter habitat use influenced breeding season phenology in these birds.
- Experimental evidence for an impact of anthropogenic noise on dawn chorus timing in urban birds
- Abstract: Many animal species are living in urban areas, where they encounter human‐altered environmental conditions. Artificial light and traffic noise are two of the most prominent anthropogenic factors, both of which potentially affect animal life. Here we studied the changes in traffic noise conditions over the morning in the urban bird habitat of the city of Seville, Spain. We tested experimentally whether noise from human activities can cause a shift in the timing of birdsong activity. Our data revealed that noise conditions vary markedly among our replicate set of twelve streets. Relatively quiet streets show low base‐line amplitude levels early in the morning, with frequent events of brief noise bursts, followed by a strong rise in noise levels. Relatively noisy streets have high base‐line amplitude levels from a much earlier start in the morning. Experimental exposure data revealed a noise‐related earlier start of dawn singing for two out of six species: the spotless starling Sturnus unicolor and the house sparrow Passer domesticus. Our experiment did not cover earlier singing species and revealed no impact for species with more‐variable starting times of the dawn singing. Our study provides more insight into the intertwinings of bird and human behavior and confirms the potential for experimental approaches to successfully tackle questions related to the impact of anthropogenic factors on animal life in cities.
- Abstract: Many animal species are living in urban areas, where they encounter human‐altered environmental conditions. Artificial light and traffic noise are two of the most prominent anthropogenic factors, both of which potentially affect animal life. Here we studied the changes in traffic noise conditions over the morning in the urban bird habitat of the city of Seville, Spain. We tested experimentally whether noise from human activities can cause a shift in the timing of birdsong activity. Our data revealed that noise conditions vary markedly among our replicate set of twelve streets. Relatively quiet streets show low base‐line amplitude levels early in the morning, with frequent events of brief noise bursts, followed by a strong rise in noise levels. Relatively noisy streets have high base‐line amplitude levels from a much earlier start in the morning. Experimental exposure data revealed a noise‐related earlier start of dawn singing for two out of six species: the spotless starling Sturnus unicolor and the house sparrow Passer domesticus. Our experiment did not cover earlier singing species and revealed no impact for species with more‐variable starting times of the dawn singing. Our study provides more insight into the intertwinings of bird and human behavior and confirms the potential for experimental approaches to successfully tackle questions related to the impact of anthropogenic factors on animal life in cities.
- The effects of nest size and insulation on thermal properties of tree swallow nests
- Abstract: The nest environment can have important influences on incubation behavior and nestling development in birds. Nest thermal properties, particularly nest composition and size, can have a major influence on heat loss. To examine the role of nest size and insulation on clutch cooling rates, we collected tree swallow Tachycineta bicolor nests and measured the cooling rate of eggs in a controlled thermal environment. We also examined the thermal benefits of nest feathers by comparing the cooling rates of nests with and without feathers. Nests with more feather insulation and heavier, deeper cupped nests cooled at slower rates. In addition, nests with feathers cooled at much slower rates than did the same nests without feathers. Our results show that nest insulation and size play important roles in nest cooling rates, which may ultimately affect incubation costs and thus reproductive performance.
- Abstract: The nest environment can have important influences on incubation behavior and nestling development in birds. Nest thermal properties, particularly nest composition and size, can have a major influence on heat loss. To examine the role of nest size and insulation on clutch cooling rates, we collected tree swallow Tachycineta bicolor nests and measured the cooling rate of eggs in a controlled thermal environment. We also examined the thermal benefits of nest feathers by comparing the cooling rates of nests with and without feathers. Nests with more feather insulation and heavier, deeper cupped nests cooled at slower rates. In addition, nests with feathers cooled at much slower rates than did the same nests without feathers. Our results show that nest insulation and size play important roles in nest cooling rates, which may ultimately affect incubation costs and thus reproductive performance.
- Sex‐specific effects of yolk androgens on begging behavior and digestion in pied flycatchers
- Abstract: The hormonal environment during early development, such as maternally derived androgens in bird eggs, has been shown to shape offspring in ways that may have important short‐ and long‐term consequences for phenotype and behavior. However, studies on the effects of androgens on begging behavior and growth in birds have provided variable results and sex‐specific effects are not well understood. We experimentally elevated yolk androgen levels in whole clutches in a passerine bird, the pied flycatcher Ficedula hypoleuca and studied effects on male and female begging behavior, ingestion and digestion. Yolk androgen elevation led to shorter latencies to beg in both male and female nestlings but to greater begging rates only in males. Both responses could be used as cues to solicit more food from parents. Yolk androgens had no effect on food intake, fecal wet mass or fecal water content. However, the proportion of organic matter in feces was lower in androgen‐treated than control males, potentially suggesting that the androgen‐treated individuals had more efficient digestion. We discuss the alternative pathways of effects of yolk androgens on begging, growth and digestion. If the effects of yolk androgens on phenotype and behavior are causally linked, there is less scope for the mother to adjust specific offspring traits independently from other traits. The sex‐specific effects of yolk androgens should be studied more, also in within‐clutch context, as the costs and benefits for each sex may further differ in relation to hatching order.
- Abstract: The hormonal environment during early development, such as maternally derived androgens in bird eggs, has been shown to shape offspring in ways that may have important short‐ and long‐term consequences for phenotype and behavior. However, studies on the effects of androgens on begging behavior and growth in birds have provided variable results and sex‐specific effects are not well understood. We experimentally elevated yolk androgen levels in whole clutches in a passerine bird, the pied flycatcher Ficedula hypoleuca and studied effects on male and female begging behavior, ingestion and digestion. Yolk androgen elevation led to shorter latencies to beg in both male and female nestlings but to greater begging rates only in males. Both responses could be used as cues to solicit more food from parents. Yolk androgens had no effect on food intake, fecal wet mass or fecal water content. However, the proportion of organic matter in feces was lower in androgen‐treated than control males, potentially suggesting that the androgen‐treated individuals had more efficient digestion. We discuss the alternative pathways of effects of yolk androgens on begging, growth and digestion. If the effects of yolk androgens on phenotype and behavior are causally linked, there is less scope for the mother to adjust specific offspring traits independently from other traits. The sex‐specific effects of yolk androgens should be studied more, also in within‐clutch context, as the costs and benefits for each sex may further differ in relation to hatching order.
