Journal of Avian Biology最新文献

Sexual dimorphism in vocal signals is found across many bird species. By evaluating correlations among sex, behaviors, and vocalizations, the meaning and utility of sound production may be inferred. Anna's hummingbirds Calypte anna exhibit pronounced sexual dimorphism, with males being larger and having more vibrant coloration than females, but vocal dimorphism in the species is less studied. A common vocalization of Anna's hummingbirds is the chip note, which is produced by both sexes in a wide array of contexts. Here, we correlated temporal parameters of recorded chip notes with individual sex and behavioral contexts gathered from field observations. The production rate of chip notes differed significantly between male and female hummingbirds but did not vary much with behavioral context. Although Anna's hummingbirds produce chips across a broad spectrum of behaviors, dimorphic chip production may be especially important in territorial behavior.

Effective conservation management of wildlife species depends on understanding their space and habitat use. Telemetry has become the primary source of data for information on how species use space and habitats. However, animals can be difficult to capture, leading to limited sample sizes and thus low quality inferences. As some individuals may be easier to capture than others, it may be tempting to use them to make inferences about the studied population as a whole. Juvenile birds, in contrast to adults, are easy to capture while they are still in the nest. However, there are few studies on when and how they might serve to obtain a representative characterization of the habitat or space use of adults. This study investigated this by using GPS-tracking data of 35 adult/juvenile dyads of golden eagles Aquila chrysaetos, with the juvenile and adult in a dyad sharing the same home-range. We assessed juvenile-to-adult home-range overlap and also compared their relative use of habitats within that space. We also analysed how these metrics evolved throughout the post-fledging dependence period (PFDP). During this period, juvenile-to-adult similarity was more than 80% for the entire home-range, whereas it was lower for the core area (approximately 60%). Habitat-use similarity was high, at approximately 90% for both the home-range and core area, both in land-cover and topography. The similarity increased following the improvement of juvenile flight skills over a period of two months, to the extent that two months after fledging and until the end of the PFDP, habitat and space use of juveniles can be used to infer the home-range and habitat requirements of adults. It would be valuable to study this ‘adult-by-juvenile replacement' approach in other species to determine whether it could be generalized, notably for species with a shorter dependence period or more complex social interactions.

Feathers are structures unique to birds that serve important functions such as flight, thermoregulation, and communication. Bacteria that live on the feathers, particularly ones that can break down keratin, have the potential to damage feathers and disrupt their use in communication. We predicted that birds could behaviorally manage their feather bacterial abundances by preening their feathers. We also predicted that individuals with lower feather bacterial abundances would have brighter and more colorful feathers. To test these predictions, we measured the amount of time individuals in a colony of captive Indian peafowl Pavo cristatus spent preening their feathers. We also collected feathers to determine bacteria abundance on the feather surface and to measure feather coloration. We found that birds had lower feather bacteria levels when they spent more time preening their own feathers, but only in female birds. We also found that bacteria abundances were not correlated with any feather color variables we measured. These results suggest that birds can manage feather bacterial abundances by preening but feather bacteria may not influence feather coloration in this species.

Alternative reproductive tactics enable individuals to choose a reproductive tactic relative to their status and prevailing environmental conditions in a way that increases their fitness. For example, females in many avian species show phenotypic plasticity and employ alternative reproductive tactics to cope with changes in predation risk and climate. Conspecific brood parasitism (CBP), in which females lay eggs in nests of conspecifics, is one example of such behaviour. It has been proposed that when prospects for successful nesting are low and/or costs of reproduction are high, females employ tactics of low effort such as non-breeding and parasitic laying. When environmental conditions are ideal and prospects for success high, females can increase their reproductive effort above typical nesting by laying parasitic eggs prior to initiating their own nest. Here, I used this flexible life-history strategy concept and long-term (1994‒2022) population level data of the common goldeneye Bucephala clangula to study how the rate of parasitic laying varies in relation to variation in nest predation risk and in the timing and length of the breeding season, the latter being measured by the timing of ice breakup. Nest predation rate in the previous year and timing of ice breakup interactively affected parasitic laying, the rate of parasitic laying being particularly high in years with late ice breakup and high nest predation rate in the previous year. Furthermore, the proportion of predated eggs was lower in parasitized nests than in non-parasitized nests, while the opposite was true for the proportion of eggs that failed in other way. As a consequence, the final number of young produced per nest was higher for parasitized nests. The findings of this study show that changes in environmental conditions affect the dynamics of alternative reproductive tactics in goldeneyes, with consequences to population level reproductive output.

The avian life cycle is composed by a progressive sequence of life history stages (LHS). Changes in energy expenditure and exposure to stressors at different LHS require corresponding changes in behavior, physiology, and morphology. Variation in hematological parameters, such hematocrit (Hct), hemoglobin (Hb), and heterophil to lymphocyte ratio (H/L ratio), can have permissive, stimulatory, and preparative actions to help maintain homeostasis through different LHS. Few studies have examined differences in these parameters among different LHS in free-living birds, with most of them restricted to temperate zones. We collected blood samples and measured hematological parameters every week for over a year from a population of a common resident bird species in southeastern Brazil, the pale-breasted thrush Turdus leucomelas. Hematocrit and hemoglobin concentration were highest during the onset of the reproduction and lowest during molt. Furthermore, H/L ratios were higher at the end of the reproduction, indicating that the breeding season could be the most stressful period of the year for this population of thrushes. There was no difference between sexes for any hematological parameter at any LHS. These results show that there is a permissive physiological effect for Hct and Hb to facilitate LHS transitions and that reproduction could be the most stressful event for this species. Lastly, these results mirror those from temperate species despite distinct environmental differences between these regions.

Under the current pattern of climate change, mountain bird populations are generally shifting their ranges to higher elevations, tracking their climatic optima. Nevertheless, space limitations at high altitudes constrain mountain species' resilience to climatic change, making them particularly vulnerable. In extreme cases, the climatic niche of some species can move beyond mountaintops, ultimately driving such species to extinction. This study presents the case of the northern wheatear Oenanthe oenanthe in mainland Spain and compares its breeding distribution from 2003 to 2022. Spain, where the species mostly occupies mountain areas, represents its southernmost distribution limit in Europe. We built environmental favourability models using information from the two most recent Spanish bird atlases and a set of climatic, topographic, human activity and lithological variables to determine the factors affecting the occurrence of the species. The influence of climate compared to all other factors was obtained using variation partitioning analysis. The northern wheatear has suffered a strong reduction (67%) in occupied areas and also in favourability throughout mainland Spain (especially in the south) where climate change may have far-reaching consequences, including local extinctions. Climate explained more than 90% of the variation in the model obtained for 2022. Interestingly, the occupied areas were, on average, 100 m higher in 2022 than in 2003. If the effects of climate warming persist, the northern wheatear will likely disappear in its southernmost distribution limit, being the Sierra de las Nieves National Park population the most vulnerable in mainland Spain. For this reason, it is necessary to implement monitoring programmes for northern wheatear populations, with priority for mountain systems wherein they already occupy higher elevations, as well as further studies on other mountain species.

Most migratory birds return every year to the same breeding sites and some species show a similarly high fidelity to wintering grounds as well. Fidelity to stopover sites during migration has been much less studied and is usually found to be lower. Here, we investigate site fidelity and distance to previously visited sites throughout the annual cycle in the common cuckoo, a nocturnal trans-Saharan migrant, based on satellite-tracking data from repeated annual migrations of thirteen adult males. All birds (100%) returned to the same breeding grounds, with a median shortest distance of only 1 km from the locations in previous year. This was in strong contrast to a much lower and much less precise site fidelity at non-breeding sites during the annual cycle: In only 18% of the possible cases in all non-breeding regions combined, did the cuckoos return to within 50 km of a previously visited non-breeding site, with no significant differences among the main staging regions (Europe in autumn, Sahel in autumn, wintering in Central Africa, West Africa in spring, Europe in spring). The shortest distance to a previously visited non-breeding site differed among the staging regions with median shortest distances for the longest stopovers of 131 km [2;1223] (median [min;max]) in Europe, 207 km [1;2222] in Sahel in autumn and 110 km [0;628] in Central Africa. The distance to a previously visited staging site decreased with the time spent at the stopover in a previous year. Understanding the drivers of recurrence and site selection in migratory birds are important for guiding conservation efforts in this group but further studies are needed to establish whether the patterns observed in cuckoos are general among terrestrial migrants with continuous distribution of habitat.

Avian preen gland helps birds cope with their environment, although its overall functioning remains unclear. We shed light on the complexity of the preen gland's functioning by studying how multiple factors associate with gland morphology (size and shape) and physiology (wax secreted) in barn owls Tyto alba. Individual factors (sex, breeding stage, body condition) were more important predictors of preen gland than environmental factors (temperature, humidity, brood size). Sex, depending on breeding stage in adults, influenced preen gland traits, pointing to the preen gland's regulation by sex hormones and a greater pressure on females to protect their eggs, offspring and themselves throughout reproduction. Adults and fledglings in better condition had larger glands, pointing to the existence of physiological costs. Temperature and humidity, in interaction with plumage coloration, also influenced but to a lesser extent preen gland traits, suggesting that melanin pigmentation and preen gland act as superseding mechanisms when protecting plumage against microorganisms. Finally, fledglings living in larger broods had larger glands, suggesting a role for the social environment in preen gland's functioning. Overall, our study supports the idea that preen gland functions in diverse biological contexts within the same species and is thus subject to multiple selective pressures.

The evolution of interspecific mimicry does not always result in perfect resemblance between mimics and models. Differences between members of a mimicry complex can be explained by genetic or developmental constraints. Alternatively, imperfect mimicry might be the outcome of a tradeoff between multiple selective pressures. In this study, we explored the evolutionary conflict between mimicry and hybridization in woodpeckers. Based on the selective tradeoff hypothesis, we expected that mimicry complexes will start to evolve once the constraint of maladaptive hybridization is relaxed. Hence, we predicted limited overlap in the divergence times between hybridizing species pairs and members of a mimicry complex. This prediction was supported by clear tipping point in the probability of hybridization and mimicry at ca 9 million years of divergence. Around this timepoint, the probability of hybridization approaches zero while the probability of belonging to a mimicry complex increases. This finding is only correlational and remains to be confirmed in other taxonomic groups. Nonetheless, our results suggest a selective tradeoff between evolving interspecific mimicry and avoiding maladaptive hybridization in woodpeckers.