Journal of Avian Biology最新文献

The ecological pressures that maintain the behavioral preferences of avian migrants, such as the timing and duration of nocturnal flights, remain elusive yet are critical to understand the evolution of the migratory program. In this study, we use an atypical light condition – extremely short to non-existent nights at high latitudes – to study responses to a forced tradeoff between nocturnality and migratory flight duration. Through this lens, we aim to elucidate the relative importance of the pressures shaping the dynamics of migratory flights. We use next-generation radar (NEXRAD) data from seven stations across Alaska to characterize the timing of peak migratory activity relative to dusk, the duration of elevated migratory activity, and the fraction of migratory activity falling within the night. We find that as night lengths decrease, the timing of peak migration clusters tightly around solar midnight, resulting in peak activity occurring slightly closer to dusk. Meanwhile, the duration of elevated migratory activity, while becoming less variable, is largely maintained, resulting in a major shift towards diurnal migration as night lengths decrease below the average duration of nightly migratory activity. These results demonstrate that the stabilizing pressure on the times during which migrants fly is strong and generally overrides the pressure of maintaining nocturnal migration, contextualizing geographic variation in migratory dynamics across Alaska, and elucidating the structure of decisions that determine migratory behavior.

Parental investment theory proposes two non-mutually exclusive hypotheses to explain variation in anti-predator behaviour in relation to the age of offspring: the ‘reproductive value of offspring' hypothesis and the ‘harm-to-offspring' hypothesis. The relative contribution of the two factors underlying the hypotheses – reproductive value and harm – may change depending on environmental conditions such as food availability. To test the relative importance of the two hypotheses under different food conditions, we conducted a supplementary feeding experiment in red kite Milvus milvus breeding pairs and used a live eagle owl Bubo bubo as a decoy nest predator to trigger anti-predator behaviour. We used capture probability and time-to-capture in mist nets mounted next to the decoy predator as a proxy for mobbing intensity. Under natural food conditions, we found a nearly constant mobbing intensity throughout the entire nestling period. However, under food-enhanced conditions, mobbing intensity was reduced in parents with young nestlings and increased in parents with old nestlings. These results suggest greater importance of the ‘reproductive value of offspring' hypothesis in situations of favourable food availability. Moreover, mobbing intensity depended on brood size and weather conditions. The results suggest that parental anti-predator investment is shaped by both offspring vulnerability and offspring reproductive value, with changing contributions in relation to offspring age. Thus, parental predator responses are dynamically adjusted to the current environmental conditions affecting vulnerability and reproductive values of offspring as well as parental predation risks.

Migration is an energy-intensive phase of birds' life cycle, often including the crossing of large ecological barriers during non-stop flights. Corticosterone (CORT), an adrenocortical hormone also known as the stress hormone, generally rises at the onset of migration to facilitate and sustain high-energy metabolism. Although birds can select favourable meteorological conditions at departure, weather variability en route may affect the migrants' energy reserves and their ability to cope with other stressors. This study investigated the effects of weather conditions on the physiological status of two nocturnal trans-Saharan species, the common whitethroat Curruca communis and the garden warbler Sylvia borin, upon arrival at a stopover island after crossing the Mediterranean Sea during pre-breeding migration. We assessed fuel stores and CORT variations in relation to tailwinds and air temperature experienced over the sea route. Birds that arrived at the stopover site with residual energy reserves after encountering moderate headwinds or lower temperatures had similar baseline CORT concentrations compared to those that migrated with tailwinds and higher temperatures. While both species exhibited a normal stress response to catching and handling, stress-induced CORT levels were correlated with higher temperature only in garden warblers. Our study provides novel insights into CORT dynamics, suggesting that nocturnal migratory Passerines are not largely affected by weather variability across a marine barrier during pre-breeding migration if they have sufficient energy reserves.

Although the negative impact of human-induced environmental effects on bird populations has been widely demonstrated, the question of whether adaptive strategies may potentially arise as a result of unforeseen challenges is still unclear. Despite their obvious pervasive effect, human-induced perturbations may activate, under certain circumstances, physiological and behavioural compensatory mechanisms that allow individuals to cope with stressful environments. In this Viewpoint, we highlight that understanding such compensatory responses (or the lack of them) requires adopting an ontogenetic and transgenerational perspective, as well as a multidisciplinary approach that integrates physiology, ageing biology and related molecular processes, and behaviour. During development, an organism's phenotype is subject to reorganization in response to environmental input. Thus, we focus on how early-life (human-induced) experiences potentially shape, even prenatally, specific physiological and molecular processes (i.e. protection against oxidative damage and telomere maintenance mechanisms), or lifelong reproductive strategies (i.e. maternal allocation into eggs), and how these, in turn, may activate physiological and behavioural adjustments across generations. To test whether adjustments in the developmental trajectory may allow individuals to make ‘the best of a bad situation' or even increase their performance (or that of their offspring) in anthropogenic environments, we call for studies that use a lifelong approach and explore transgenerational effects. We also propose experimental designs to help advancement in the field.

Animals' performance of basic functional behaviours, such as foraging and movement, may improve with age as a result of past experiences. In migratory birds, for example, due to earlier or more efficient migration, older and likely more experienced individuals tend to arrive at breeding sites earlier and enjoy better breeding conditions than younger conspecifics, resulting in a higher reproductive success. Yet, despite the advantages of early arrival for breeding adults, the long-term effects of fledging early and/or with a higher body condition on chicks' future fitness prospects remain largely unexplored. In differential migration systems, low-quality or socially subordinate individuals may be constrained to sub-optimal migratory behaviours associated with lower demographic rates. Therefore, producing high-quality chicks may enhance the survival of offspring. In this study, we analysed data from the long-term ringing programme on the breeding population of Eurasian spoonbills in the Camargue (southern France) to investigate how breeder age may influence the timing of breeding and, in turn, how this may affect chick body condition and their subsequent migratory behaviour. Using breeding resightings of birds individually marked as a chick since 2008, combined with chick biometric measurements and subsequent winter resightings of offspring, we show that older spoonbills tend to breed earlier in the season than younger individuals, and that early breeders, regardless of age, are more likely to produce chicks with higher body condition than late breeders. Finally, migratory behaviour of juveniles appears to be influenced by the timing of breeding, with later-born juveniles tending to undertake less demanding migrations (without crossing major ecological barriers) than juveniles born earlier in the breeding season. Our study therefore highlights the relevance of long-term studies to better understand the complex breeding phenology of migratory species, which can lead to changes in population-level patterns and processes.

Bird populations in Europe and North America have been strongly declining for the last 40 years. As mobile organisms, bird species are sensitive to landscape patterns; therefore, landscape effects on bird communities need to be understood to set relevant conservation measures. However, forest bird communities have received much less attention than their counterparts in agricultural landscapes in this respect. In this systematic review, we investigated the effects of landscape heterogeneity on bird communities in forest contexts by searching for empirical studies conducted in the boreal, montane, and temperate biomes. We found 45 articles from which we extracted 1272 single results (i.e. tested relationships between landscape and biodiversity metrics). We found that most of the articles studied local alpha-diversity (78%; 22% for landscape gamma-diversity) during the breeding season (87%). In contrast, most of the significant results were related to bird gamma-diversity, indicating a positive effect of landscape heterogeneity. Most of the tested landscape metrics were related to compositional heterogeneity (74%). Overall, habitat amounts had a large positive effect on their related communities (i.e. forest amount on forest bird species). However, forest composition variables (e.g. broadleaf forest proportion) mostly led to non-significant effects. While we found antagonistic results depending on bird habitat preference, groups based on migration strategy were largely unresponsive to landscape variables. However, we failed to find a consistent scale of effect across studies. We discuss the potential landscape mechanisms at play, such as niche partitioning, edge effects, and habitat complementation. We recommend better acknowledging forest ecosystem complexity and variability in future forest landscape studies and better recognition of bird habitat requirements beyond the breeding season (including overwintering sites and migration stopovers).

The use of global positioning system (GPS) tags is increasingly widespread for wildlife tracking in many ecological studies. However, GPS tags are often too heavy for lightweight species or require recapturing the animal to download the data. In this study, we designed a water-soluble backpack harness linked to a handmade GPS+VHF tag combination to obtain GPS data without the need to recapture the animal. Once the harness disintegrates after rainfall, the GPS+VHF tags can be located via radiotracking, and the dataset can be downloaded. Specifically, we 1) assessed the most effective way to attach the VHF tag to the GPS (to minimize data loss in terms of quantity and quality), 2) tested effects on wild birds, and 3) evaluated the efficiency of device retrieval by tagging Dupont's larks Chersophilus duponti, a small (~ 40 g), elusive passerine. Results showed that the VHF tag should be attached to the GPS at a 45º angle to avoid negative effects on GPS data. To reduce GPS location error, we recommend using data obtained with ≥ 5 satellites and, ideally, > 7 satellites, for average errors less than 10 m. All devices (100%) were detached from the birds and successfully retrieved. No adverse effects were detected in the birds after the tagging period, and all birds remained in their territories. This methodology can be highly useful for studies involving lightweight and elusive fauna. Additionally, our system reduces stress on individuals by minimizing the number of captures required, while also lowering human resource costs, as a single person can carry out the entire process.

Factors outside the breeding season can affect population trends for migratory species. Yet information on population-specific migration and nonbreeding ecology for most species is lacking, complicating conservation efforts. Louisiana waterthrush Parkesia motacilla and worm-eating warblers Helmitheros vermivorum are Nearctic–Neotropical migratory songbirds that share breeding habitat associations, and occur in sympatry throughout most of their breeding distributions. Yet these species exhibit variable regional population trends on the breeding grounds, suggesting that processes outside of the breeding period may impact population growth. We used light-level geolocators to track Louisiana waterthrush and worm-eating warblers from four sites spanning their breeding distributions (Arkansas, Tennessee, Ohio, and Pennsylvania, USA). We describe the geographic distribution of populations during the nonbreeding period and quantify interspecific variation in the timing of migration to assess the potential for factors outside the breeding period to impact population dynamics. From 2016 to 2020, we marked 153 individuals (85 Louisiana waterthrush and 68 worm-eating warblers) across the four sites, and estimated migration timing, nonbreeding locations, and migratory connectivity for 24 Louisiana waterthrush and 21 worm-eating warblers. We observed moderately strong migratory connectivity (MC) in both species (Louisiana waterthrush MC = 0.40 [0.25 SE], worm-eating warbler MC = 0.44 [0.13 SE]) between breeding and nonbreeding sites, and a high degree of overlap (i.e. > 50%) among most populations' nonbreeding core-use areas. Moreover, populations experienced largely similar environmental conditions (measured by enhanced vegetation index) during the nonbreeding period. On average, Louisiana waterthrush initiated migration ~ 40 days earlier than worm-eating warblers across the annual cycle, and this trend was strongest in southern breeding populations. These findings emphasize the value of leveraging multiple species into full-annual cycle studies to identify when and where factors limiting populations of migratory species may occur. Additionally, we demonstrate that migratory species that co-occur during stationary periods of the annual cycle (i.e. breeding and nonbreeding periods) can experience strong temporal isolation during seasonal migration.

Avian haemosporidians are a diverse group of parasites that infect birds worldwide and have been a major focus of research for decades. Yet, few studies have identified the drivers of infection at the intraspecific host level. We aimed to study the drivers of prevalence and diversity of haemosporidian parasites infecting a common North American songbird species, the American robin Turdus migratorius, which breeds across most of the continent. We found little seasonal variation in haemosporidian prevalence in robins, although we detected a significantly positive relationship between robin breeding latitude and co-infection with different haemosporidian parasite lineages. Additionally, robins infected with Plasmodium had substantially better body condition than uninfected robins, which could be due to migratory culling. We detected 31 haemosporidian lineages among the robins we sampled, of which eight were novel. When matched against known haemosporidian lineages, our results suggest that robins harbor a higher diversity of haemosporidian parasites than previously known. The results of this study suggest that comparisons of common, widespread bird species such as robins across their range could help unveil novel aspects of the haemosporidian–host relationship and how such a relationship may change under current and future rapid environmental change.

The Australian zebra finch is an arid-adapted passerine with high hygric demands, that is projected to be at risk from increasing temperature and aridity throughout its distribution by the end of the century. We examine here how individual zebra finches modify their visits to water in response to the climatic conditions of ambient temperature, relative humidity, rainfall, wind speed and day length over a two-month period during an Austral summer drought in arid central Australia. Visits to water by individual zebra finches increased with increasing ambient temperature and day length, and decreased with increasing relative humidity, wind speed and rainfall. These findings are the most comprehensive data for the pattern of visits to water by individual wild birds globally and highlight the importance of regular drinking by individual finches to maintain water balance and thermoregulation. Our data highlight the importance of water availability for birds in the arid zone in a warming climate.