Journal of Avian Biology最新文献

In birds with double-nesting and uniparental incubation, such as the rock partridge Alectoris graeca saxatilis, the male incubates one clutch, while the female incubates the other. A previous study found no significant difference in hatching and predation rates on Alpine rock partridge nests incubated by each sex. We therefore hypothesized that the incubation rhythms of both sexes would be similar. To test this, we monitored the incubation patterns of 40 nests incubated by females and 41 nests incubated by males in the French Alps between 2011 and 2020. Temperature loggers were installed within and outside the nests to record internal and ambient temperatures at 3-min intervals. Incubation recess timing and duration were inferred from the analysis of temperature curves. We employed statistical modelling to assess the effects of the incubating bird's sex, minimum ambient temperature, incubation day, clutch size, and recess rank on various incubation parameters. The timing, total duration, and number of recesses, as well as nest temperature, were found to be similar between the sexes. On average, birds took 2.5 recesses per day, with each recess lasting approximately 75 min. Overall nest attendance was ≃ 88%. Recesses occurred throughout the day, with a peak after sunrise and a second, less pronounced peak before sunset. Nocturnal recesses were rare and resulted from disturbances to the incubating bird. Modelling results indicated only slight differences in the mean recess duration between the sexes throughout the incubation period. Further analysis showed that both sexes adjusted their incubation rhythms in a similar manner in response to the progress of incubation and to daily minimum temperatures. Cold temperatures may compel parents to spend more time foraging to meet their energy needs. Rock partridges exhibited lower nest attendance compared to grouse species inhabiting cold environments, likely due to their relatively lower body reserves.

The migration patterns of birds breeding at high latitudes have undergone major changes during the Holocene, as species expanded from small refugia following the last glaciation. Unique features of genetic migration programs and species-specific dispersal patterns have resulted in various levels of migratory connectivity. High migratory connectivity can occur when populations expanding from different refugia maintain historically distinct wintering sites, or when species expanding their breeding ranges maintain a constant migratory vector. Alternatively, species may develop novel routes to nearby wintering sites during range expansion, also leading to high migratory connectivity. Here, we analyse light-level geolocator and multisensor data logger tracks of great reed warblers Acrocephalus arundinaceus from a population at its eastern range limit in Kazakhstan. We compare their migration routes with published data from five Western Palearctic populations to understand how migration patterns have evolved as the breeding range expanded. Mitochondrial DNA data suggest that Kazakhstan was colonised from the western part of the range, but the logger data show that Kazakh great reed warblers winter in East Africa together with conspecifics from Turkey. This indicates that their migration route did not arise as a simple parallel shift of an unchanged vector-based programme, but required drastic modifications of the migratory directions to maintain African wintering quarters. A remarkable finding in our study was the detection of a novel spring migration strategy. We found that birds leave the African wintering quarters already in February to spend up to two months at an intermediate staging area in southern Iraq, half-way to their breeding grounds in Kazakhstan. We call this a two-step spring migration strategy and discuss the conditions that may promote the evolution of such a behaviour.

As individual tracking devices and year-round genetic sampling become more accessible, research on the historically understudied nonbreeding period has exploded in the past decade. These studies are revealing tremendous inter- and intraspecific variation in migratory, molting, and other nonbreeding strategies, thereby informing efforts to protect bird populations throughout the entire annual cycle. However, we still have much to learn about where and when nonbreeding adaptive variation influences reproductive isolation and speciation. Previous work has demonstrated that some adaptations to conditions in different nonbreeding areas or migratory routes can fuel diversification by precluding opportunities for diverging lineages to interbreed or, in instances where lineages do interbreed, manifesting as disadvantageous phenotypes in hybrids. In this paper, we provide an overview of both established and speculative processes through which the primary nonbreeding events in the avian annual cycle (i.e. molt, migration, and overwintering) may interact to regulate gene flow between avian lineages. Although the relatively few but well-described examples of divergence in nonbreeding phenotypes contributing to reproductive isolation suggest nonbreeding divergence is a common mode of speciation in birds, a growing number of population genetic studies reporting nonbreeding divergence in the absence of reproductive isolation seemingly suggest the opposite conclusion. We outline processes that could result in this apparent contradiction and propose general comparative frameworks to test factors that may predictably mediate the relationship between nonbreeding divergence and reproductive isolation. In the past, a shortage of nonbreeding natural history and population genetic data have impeded our ability to test these predictions in more than just a few systems. We urge evolutionary biologists to pay closer attention to conservation-oriented studies, which are rapidly filling these knowledge gaps and presenting opportunities to better understand the true role of nonbreeding divergence in avian diversification.

The intense human persecution of wildlife in the past forced many animal populations to look for refuge in human-inaccessible habitats. With the decline of direct persecution, and the changes in the attitude of modern urban societies towards wildlife during the last few decades, an ecological process of abandonment of refuge habitats has become pervasive, and many species make habitat choices deemed surprising presently, such as colonizing sites that are more accessible to humans. We tested this process in the yellow-legged gull Larus michahellis by analysing long-term time series (1976–2022) of breeding pairs in seven colonies in southern Europe. Overall, yellow-legged gull numbers showed a strong pattern of decrease during the study period, due to the recent closure of open-air garbage dumps. However, while the number of pairs in colonies located in human-inaccessible sites (islets with cliffs) declined rapidly, new colonization together with a monotonic linear population growth was detected in human-accessible sites, coinciding in time with the departure from refuges. Moreover, we found that the new small yellow-legged gull colonies acted as cores for the formation of multispecies waterbird colonies likely by heterospecific attraction, that provides an added unexpected conservation value to yellow-legged gulls traditionally considered a pest species.

Birds show global declines, and understanding the relationship between avian diet and fitness can both answer basic questions in physiological ecology and inform conservation efforts. Diet-induced changes to the gut microbiome, the collection of microorganisms and their functional genes and metabolites inside the gut, may be of particular importance to avian fitness as the gut microbiome provides a suite of beneficial roles for nutrition and immunity of the host. Furthermore, evidence is growing that the gut microbiome may impact animals' diet choices, which could have cascading impacts on avian fitness. Sequencing technologies allow both diet and gut microbial composition and diversity to be characterized from the same fecal sample, creating ripe opportunities to explore diet–microbiome relationships. In this mini-review we summarize the existing literature on the effect of diet category, diet shifts, and dietary diversity on the gut microbiome, and the potential for the gut microbiome to serve as a modulator of diet choice in wild birds. We list open questions in the field of avian diet–microbiome interactions and provide methodology considerations for designing studies to sample both diet and gut microbiomes. This mini-review provides a framework for understanding the reciprocal relationship between diet and gut microbiota in wild birds.

Urban ecological studies often emphasize the role of vegetation-related factors in promoting local biodiversity, but less attention has been given to human-related factors, especially in tropical assemblages dominated by native species. In this study, we assessed the role of landscape and local variables in bird species richness and abundance in Medellín (Colombia), based on a city-wide survey (n = 212). We recorded 87 resident bird species, 97% of which were native, including the two species categorized as highly-abundant. Highly-abundant species showed mostly positive relationships with human activities (i.e. pedestrians and motorized vehicles), though only at the abundance level. In contrast, moderately-abundant species showed mostly negative relationships with both human activities and urban infrastructure (e.g. buildings, motorized vehicles), but mostly at the species richness level. Species richness of moderately-abundant species increased particularly at sites with low to intermediate fragmentation levels and landscape proportion of green cover, where the number of vegetation layers increased. Lowly-abundant species showed the strongest negative relationships with human activities and urban infrastructure, at both the species richness and abundance levels, particularly in sites with higher green cover fragmentation and lower landscape proportion of green cover. Interestingly, highly-abundant species abundance, and lowly-abundant species richness and abundance showed significant negative relationships with distance to the city border, but only the lowly-abundant species showed substantial spatial autocorrelation within the city. Our findings suggest that in Medellín, human-related factors can strongly constrain urban bird diversity. Therefore, given the substantial management limitations found in the most intensely urbanized environments, if we aim to promote biodiversity conservation across highly dense urban landscapes, it is important to reduce human-related constraints in sites with intermediate to low urbanization levels. Additionally, we should protect green cover remnants in areas with low urbanization levels and nearby non-urban areas.

Migratory animals often display remarkable adaptations in order to successfully complete their journeys. While there is substantial evidence on immunomodulation during breeding and at stopover sites en route, the immune status of migratory birds upon reaching their non-breeding grounds and throughout this stationary season remains poorly understood. Here we used the Hudsonian godwit Limosa haemastica—an extreme long-distance migrant that breeds in the Arctic and spends the non-breeding season in Patagonia—to investigate constitutive immune function (CIF) in adult individuals under contrasting conditions: on birds moulting primary feathers when they had recently arrived at non-breeding grounds (post-arrival birds), and four months later on birds moulting into breeding plumage, a couple of weeks before their departure to breeding areas (pre-migratory birds). We found comparable CIF between post-arrival and pre-migratory birds. When each group was analysed separately, agglutination titres and bacterial killing ability increased as birds completed their breeding plumage moult, although the association with bacterial killing ability appeared to be driven primarily by males. Bacterial killing ability was also higher in pre-migratory females than in males. None of the evaluated CIF parameters were affected by primary feather moult in post-arrival birds. Our results suggest important immunomodulation occurring at the end of the non-breeding season in pre-migratory godwits, probably due to the profound physiological and metabolic changes required in preparation for endurance migration. Our work contributes to the little-known topic of immune dynamics in extreme long-distance migratory birds across the non-breeding season.

DNA methylation, which can change within-individuals over time and regulate gene expression, is important to many aspects of avian biology. It is particularly important in avian responses to various stressors associated with introductions, such as infection and environmental changes. However, it remains unclear whether native and introduced bird populations differ in their epigenetic responses to stressors, and how DNA methylation may contribute to the success of non-native populations because of the limited availability of epigenetic studies. To address this knowledge gap, we used epiRADseq to investigate changes in DNA methylation within-individual house sparrows Passer domesticus prior to and eight hours after a simulated bacterial infection. We compare wild-caught house sparrows from introduced populations with those from native populations, assessing the number of genomic locations that exhibit changes in methylation, the magnitude of those changes, and the variance among individuals. Our results show that individuals from introduced populations experience more widespread changes in DNA methylation, with greater magnitude and higher variance, compared to their counterparts from native populations. These findings suggest that DNA methylation plays a significant role in an individual's response to infection. They also indicate that individuals from introduced populations may exhibit distinct epigenetic responses compared to their native counterparts, consistent with the concept of epigenetic buffering.

Prevailing theory suggests that sex ratios of offspring at birth should not differ from parity if costs of producing offspring of both sexes are similar. However, offspring sex ratios may deviate from parity when there is sex specific variation in fitness returns. We assessed offspring sex ratios of eastern wild turkeys (Meleagris gallopavo silvestris) across the southeastern United States by molecular determination of sex from eggshell membranes of hatched clutches. Our objective was to evaluate whether offspring sex ratios differed from parity and to examine potential drivers of variation in offspring sex ratios across and within our study sites. We sexed 724 offspring from 83 nests using molecular markers and identified 278 males and 446 females, with a sex ratio of 38% male. We found that offspring sex ratios were biased towards females on three hunted study sites but did not differ from parity at our remaining non-hunted site. Specifically, on sites with spring hunting, where male mortality was increased due to harvest, the probability of producing male offspring was 47% lower than on our non-hunted site. Our findings suggest that female wild turkeys may adaptively adjust the sex ratio of their offspring based on predictable, sex specific mortality, favoring the sex with higher survival, thereby enhancing their lifetime fitness. Our results provide insights into reproductive strategies of wild turkeys and the influence of hunting on sex ratios in Galliform offspring.

Sleep is an evolutionarily conserved behaviour critical to animal function. While the exact functions of sleep are still unclear, the ubiquity of sleep behaviour and its potential high costs (e.g. reduction in foraging time, increased vulnerability to predators) suggest sleep serves a critical role for animals. Animals that share environments with humans, such as urban birds, face numerous anthropogenic stimuli that are likely to fragment or alter their sleep. In this literature review, we synthesise the current research available on sleep disturbance in birds and provide suggestions for future research to address key gaps. Our analysis revealed that knowledge on how sleep disturbance affects birds is currently fragmented, is often inferred rather than explicitly measured, and fails to connect causal mechanisms to ecologically relevant outcomes. To address these critical knowledge gaps, we suggest that future research on sleep should: 1) incorporate both the effect of stimuli on sleep and the resulting consequences of this sleep loss on the behaviour and fitness of the study species; 2) broaden to include contexts other than migration and seasonal change; 3) include juvenile birds that are still in the development phase; and 4) explore a greater range of the potential functional consequences of disrupted sleep. Understanding the fitness-related consequences of sleep disturbance from anthropogenic stimuli will provide critical insights into the impact of these stimuli on birds, and how to mitigate the impacts of sleep disturbance in urban environments.