Journal of Avian Biology最新文献

Birds that repeatedly visit distinct places along their migratory routes in consecutive years must be able to navigate to these places and respond appropriately to unfavourable wind conditions. This study analysed the migratory routes, repeatedly-visited areas and responses to sidewinds of 15 GPS-tracked adult ospreys Pandion haliaetus from northeast Germany migrating to their wintering sites in Africa and back. We determined stopovers and intermediate goal areas and performed repeatability estimations on timing and migratory paths in four regions. The orientation behaviour of the ospreys was analysed with regard to perpendicular wind components at each GPS point during autumn and spring migrations. Generalised linear mixed models were used to test the dependence of orientation behaviour on region and the distance to the next goal. The findings showed that ospreys demonstrate high fidelity to migratory paths in autumn and spring, as well as to the timing of migration in autumn; and sidewinds are predominantly compensated, especially when sidewinds are strong. Furthermore, during autumn migration, the proportion of compensation increases in most regions with decreasing distances to the next goal; however, during spring migration, drift behaviour was detected more often at smaller distances to the next goal than at higher distances in the regions Mediterranean and central Europe. In general, ospreys compensate for unfavourable sidewinds and utilise supporting tailwinds on their journeys to the wintering sites in Africa and back to central Europe.

Understanding how habitat structure relates to reproductive performance of species can help identify what habitats are of the highest quality for a given species and thereby guide effective management. Here, we compared the influence of prey abundance and the amount of shelter area on the relationship between habitat and breeding performance. We focused on the forest-dwelling northern goshawk Accipiter gentilis in an agroforestry system. Using structural equation modelling, we tested the associations between reproductive performance and three explanatory factors: habitat structure, abundance of food resources or levels of mobbing disturbance, and prey supply to the nest. Our results suggest that habitat structure influences reproductive performance through shelter rather than through prey abundance. During the study period, forested habitats in the breeding territories provided shelter to the goshawk, reducing disturbance by carrion crows Corvus corone, which acted as large, aggressive, social mobbers. Decreased disturbance increased prey supply to the nest, probably because it favored food accessibility and male goshawk foraging efficiency. Habitat was not significantly associated with quality of the breeders, both in terms of body size and seniority in the territories. Our findings suggest that reproductive performance, and therefore habitat quality, may depend more on sheltered access to food resources than on the amount of food available. Our observation that mobbers decrease predator foraging efficiency highlights the possibility of designing effective, socially acceptable predator management strategies to protect sensitive domestic prey.

Understanding how reproductive isolation arises and accumulates between incipient species is an important goal of evolutionary biology. Patterns of interspecific hybridization in naturally occurring hybrid zones can provide an important insight into this process since they reflect the strength, symmetry and nature of reproductive barriers separating the species. Here we studied patterns of hybridization in two closely related passerine species, the common nightingale Luscinia megarhynchos and the thrush nightingale L. luscinia, that diverged ~1.8 Mya and co-occur in a secondary contact zone spanning across Europe. Genome-wide genotyping of more than three hundred individuals from the sympatric population and adjacent allopatric populations revealed that the vast majority of sympatric individuals were pure parental species. Only 6.5% of sympatric individuals were hybrids, from which 3.4% were F₁ hybrids and 3.1% backcross hybrids from the first to the fifth backcross generation. Most F₁ hybrids arose from the cross of a thrush nightingale female and a common nightingale male. F₁ hybrids showed intermediate morphology and could be distinguished with high confidence from the parental species based on several diagnostic traits. However, backcrosses were morphologically difficult to distinguish from the parental species from which they inherited most of the genome. Our results suggest strong, yet incomplete, reproductive isolation between the two nightingale species both at a prezygotic and postzygotic level. Nightingales thus represent a useful model system for exploring the late stages of speciation with ongoing gene flow after secondary contact.

Songbirds on migration spend a greater share of their travelling time at stopover sites in order to rest, recover and refuel compared to actively flying. In the German Bight of the North Sea, two subspecies of the northern wheatear split travelling routes, with Greenlandic/Icelandic breeders (subspecies leucorhoa) facing a long over-sea flight and Scandinavian breeding birds (subspecies oenanthe) travelling further roughly along the coast. We used automated radio-telemetry in spring to show that leucorhoa birds stayed significantly longer at a coastal stopover site and clearly selected for favourable weather, especially easterly winds, when resuming flights. Conditions for departures of individuals from the subspecies oenanthe were less obvious. They were more likely to depart on nights with southerly winds, often along with rising air temperatures, while air pressure dropped. Individuals of subspecies leucorhoa thus wait for optimal flying conditions to resume for longer flights, while oenanthe birds, with shorter distances ahead, seem to optimise time by leaving the stopover site more quickly. Our dataset thus confirms that songbirds optimise stopover based on their (sub)species-specific migration patterns.

Living with increasing urbanisation and human populations requires resourcefulness and flexibility in wild animals' behaviour. Animals have to adapt to anthropogenic novelty in habitat structure and resources that may not resemble, or be as beneficial as, natural resources. Herring gulls Larus argentatus increasingly reside in towns and cities to breed and forage, yet how gulls are adjusting their behaviour to life in urban areas is not yet fully understood. This study investigated wild herring gulls' responses to novel and common anthropogenic objects in urban and rural locations. We also examined whether gulls' age influenced their object response behaviour. We found that, out of the 126 individual gulls presented with objects, 34% approached them. This suggests that the majority of targeted gulls were wary or lacked interest in the experimental set-up. Of the 43 gulls that approached the objects, we found that those tested in urban locations approached more slowly than their rural counterparts. Overall, gulls showed no preference for either novel or common anthropogenic objects, and age did not influence likelihood of approach, approach speed or object choice. Individuals paid most attention to the object they approached first, potentially indicative of individual preferences. Our findings indicated that most herring gulls are not as attracted to anthropogenic objects as anecdotal reports have suggested. Covering up obvious food rewards may thus help mitigate human–gull conflict over anthropogenic food sources.

Local population dynamics are driven by local processes such as temporal variation of productivity, survival, emigration and population stage structure, and by processes originating from outside the local population, such as immigration. Populations may operate as sources that contribute more individuals than have died or as sinks that depend on neighbouring populations. Knowing demographic processes driving the dynamics of a local population and the significance of a local population in a system of multiple populations is crucial for understanding population dynamics and requires detailed demographic analyses. We studied demographic drivers in a red kite Milvus milvus population located in Germany that was monitored for 34 years using integrated population modelling. We specified the model in such a way that the numbers of experienced breeders, local recruits, locally born non-breeders and immigrants are estimated explicitly, applied a retrospective perturbation analysis to identify the demographic drivers and assessed the source-sink status of the population. The study population increased on average by 1% per year. The number of breeders was about double than the number of locally born non-breeders, and the number of experienced breeders exceeded the number of local recruits and immigrants by a factor of six to nine. The retrospective analysis identified productivity, i.e. the number of fledglings per breeding pair, as the main demographic driver, followed by adult survival and immigration. As other studies show close links between food supply and productivity, it is likely that food supply plays a critical role in red kite population dynamics. The study population contributed more individuals than it lost through mortality, but due to emigration of locally born individuals it was not self-sustainable and depended on immigration. This quantifies the population as a dependent source and shows that red kite populations are linked across large spatial scales.

Animals breeding in nest-boxes experience nesting environments in which they did not originally evolve. Despite the central importance of nesting microclimate for offspring fitness, little is known about the thermal properties of human-provided nest sites compared to natural ones. In particular, comparisons with offspring in the nest are lacking. Here, we compare microclimate (temperature and absolute humidity) from the onset of breeding, thus starting with nest-site choice and ending with the post-fledging stage, quantified in natural cavities and nest-boxes used by several species of hollow-nesting birds in a temperate deciduous forest. We confirm that across all nesting stages, nest-boxes were thermally unstable when compared to natural cavities, with higher temperature maximums, larger amplitudes and worse insulation from maximum ambient temperatures relative to natural cavities. Surprisingly, as average humidity of natural cavities was previously shown to be higher than in nest-boxes, in the presence of actively thermoregulating young, nest-boxes were more humid than natural cavities. When offspring were in the nest, internal microclimatic shifts were mitigated three times more effectively in natural cavities than in nest-boxes (in terms of mean daily differences from ambient temperature). Artificial cavity microclimate is likely to amplify the adverse effects of projected temperature increases by compromising thermoregulation of developing animals. We stress that conservation efforts should focus on the protection of areas offering natural breeding-hollows to reduce the potential impacts of climate change on breeding animals.

The frequency of extra-pair paternity (EPP) varies widely across socially monogamous birds, but the proximate mechanisms driving this variation remain unclear. In this study, we tested two major factors hypothesized to influence extra-pair mating – breeding density and genetic diversity – by comparing genetic mating patterns in two populations of black catbirds Melanoptila glabrirostris. This Neotropical songbird is endemic to the Yucatán Peninsula, including eastern Mexico, and its offshore islands. We sampled one mainland (Sian Ka'an Biosphere Reserve) and one island (Isla Cozumel) population and used single-nucleotide polymorphisms (SNPs) to quantify heterozygosity and genetic parentage over two breeding seasons. Moderate levels of EPP occurred in both populations (9.5–35% of offspring and 17–45% of nests). Contrary to predictions, breeding density did not affect EPP: although breeding densities were much higher on the mainland than on the island, EPP rates did not differ between populations, and local breeding density was not correlated with EPP at individual nests. In contrast, partial support emerged for the hypothesis that genetic diversity influences EPP: extra-pair offspring were more heterozygous than within-pair offspring. However, the two populations did not differ in genetic diversity, and neither the heterozygosity of social fathers nor within-pair relatedness predicted EPP. These results are consistent with recent comparative studies suggesting that breeding density is not a critical driver of EPP rates, and that not all tropical songbirds exhibit low rates of EPP.

Classical models predict that male fitness is based on resources monopolized and invested in reproduction, and/or on individual quality providing offspring with sexually attractive traits or viable genes. However, these factors are frequently correlated, making their relative influence on male fitness difficult to describe and quantify. We analysed the relative influence of the main features of the sedge warbler's Acrocephalus schoenobaenus breeding system, i.e. age, arrival date, territory quality, male sexual activity (song and polyterritorial behaviour), on males' mating success, fledging success and local recruitment. Results show that this species' breeding system involves three main paths: 1) earlier-arriving males have higher mating success, regardless of territory quality, 2) the quality of territories pre-empted by earlier males directly influences recruitment and 3) mating success is influenced by male sexual activity (polyterritorial behaviour), but an additional territory also affects recruitment directly. As arrival date plays a significant role in all the paths, the whole system seems to depend on male quality; although the benefits accruing to male fitness are obtained not only through sexual selection but also through resource monopolization.

The migration phase of birds is divided into two main states: stopovers and actual migratory flights. For soaring birds, such as storks, nighttime is especially important to conserve energy and to start the next day in favourable weather conditions. Although there is a large number of recent studies on white stork Ciconia ciconia, for example using advanced technologies such as GPS technology, the nocturnal behaviour of the species is still an enigma. Thus, we GSM–GPS-tagged 90 immature storks and checked their nocturnal behaviour, especially roost disturbance, during their first autumn migration from breeding grounds in southern Poland to wintering places in Africa. Storks roosted on three types of site: on buildings, on the ground or in trees. Birds that roosted on the ground had a higher probability of nighttime disturbance than those that used trees or buildings. The probability of disturbance at night was also related to longitude and latitude; the most easterly birds and those at the start of the migration route were disturbed more often during the night. Furthermore, and interestingly, environmental conditions at roosts were also significantly related to the probability of disturbance; birds roosting at tree sites with higher NDVI (greener) and with higher levels of artificial light both had a lower probability of disturbance. A possible explanation of this could be related to lower potential predatory pressure at night. We found that after long flights birds were disturbed more often at night, and that disturbed birds migrated further the next day. For a better understanding of the nocturnal behaviour of storks, as well as of other migratory birds, the use of modern technological tools with greater precision is recommended.