Journal of Avian Biology最新文献

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.

Hover-feeding by hummingbirds from pendent flowers relative to horizontal flowers increases the metabolic cost of flight, but in nature a large proportion of hummingbird-pollinated flowers are nonetheless oriented near-vertically downward. We used binary-choice tests to assess behavioral preference of captive Anna's hummingbirds for these two particular floral orientations. The extent of nectar consumption from artificial flowers differed significantly over a 2-hour exposure period, with birds showing greater extraction from the horizontal configuration. We also found that time spent hovering at the feeder immediately prior to nectar extraction did not vary by feeder orientation, whereas feeding duration tended to be greater at horizontal feeders. Opportunistic measurements of wild hummingbirds were also consistent with a preference for horizontal feeders. In aggregate, these observations suggest that the increased metabolic cost of hover-feeding from pendent flowers is matched by an associated behavioral aversion, at least under the conditions examined here. However, pendent hummingbird-specialized flowers are common, suggesting that additional behavioral or ecological factors underpin evolutionary persistence of this floral presentation.

Phenological changes are one of the most well recognised responses of organisms to climate change. The ability to detect phenological change often relies on long-term datasets, which are scarce in the Southern Hemisphere. As the adaptive capacity of species is highly variable, it is important to better understand how species in the Southern Hemisphere may respond to climate change through shifts in their annual cycles. Citizen science projects, like bird nest record schemes, offer valuable long-term data, although data heterogeneity can pose challenges, affecting their use in research. To investigate the suitability of the South African nest record scheme (SANRS) for estimating phenological shifts, we conducted a preliminary exploration of shifts in lay dates in four well-represented species. Firstly, we explore the composition of nest cards for each species, specifically the proportions of single- and multi-visit cards. Secondly, we explore the accuracy of single-visit cards for estimating lay dates compared to more accurate multi-visit cards. Lastly, we compared analytical approaches to test for possible shifts in lay dates. We found little differences for lay date estimates between single and multi-visit cards and our different models showed similar patterns of lay date shifts for all species. Three of our four species (African paradise flycatcher Terpsiphone viridis, cape turtle dove Streptopelia capicola, cape wagtail Motacilla capensis and laughing dove Spilopelia senegalensis) showed a shift toward later laying over the period 1950–1999. Although only based on a limited number of species, this consistent pattern towards later lay dates contrasts with the general trends found in the Northern Hemisphere for shifts toward earlier laying. The mechanisms driving these shifts is currently unclear, but in contrast to the Northern Hemisphere, in this region rainfall rather than temperature may have a stronger influence on avian breeding phenology. Our results highlight the potential of the South African Nest Record Scheme to detect shifts in laying dates, paving the way for more extensive studies of phenological changes, and the mechanisms involved, in the under-researched region.

Same-sex sexual behaviour (SSB), encompassing actions such as courtship, pair bonding, and parenting between individuals of the same sex, has been observed across numerous taxa, including birds. Yet despite its widespread occurrence, SSB remains poorly understood, often dismissed as maladaptive or the result of errors in sex discrimination. However, instances of same-sex partnerships – persistent pair bonds between same-sex individuals – challenge these assumptions, particularly in birds, whose diverse mating systems and high level of monogamy imposes strong selective pressures on pair formation and maintenance. This review synthesises our current knowledge of same-sex partnerships in birds, addressing their evolutionary origins, adaptive benefits, and broader ecological significance. We argue that the prevalence of same-sex partnerships has likely been underestimated, hindered both by historical biases in interpretation and, especially more recently, logistical challenges in data collection. Drawing on examples from across the avian class, we explore the potential reproductive and social benefits of same-sex partnerships. By reframing these behaviours as potentially adaptive rather than anomalous, we aim to advance understanding of their evolutionary persistence and encourage more systematic research into their occurrence and implications.

Feather structure contributes greatly to a birds' ability to repel water, which is essential for thermoregulation and energy use. Water repellency of feathers has traditionally been inferred by measuring a structural index based on the distance between the feather radii and vane. A more direct method measures the contact angle of a water droplet resting on the pennaceous vane. This method is used for measuring the water repellency of various materials (e.g. textiles) and we considered it a standard against which the structural index can be validated. Despite widespread use of both techniques, their level of agreement with each other has not been systematically evaluated. Additionally, few studies have tested the direct contribution of uropygial oil to a feather's water repellency. We tested the correlation between the two methods, using feathers from two high-elevation species that are adapted to the cold and wet conditions of montane systems, Swainson's thrush Catharus ustulatus and Bicknell's thrush C. bicknelli. We also compared contact angles measured on feathers before and after removing their coating of uropygial oil. We found no correlation between the methods in either species, which suggests the structural index is not a reliable indicator of feather water repellency. Removing uropygial oil significantly reduced contact angles in both species, demonstrating a direct contribution of the oil to water repellency. The lack of agreement between the structural index and contact angle method may have occurred because the structural index infers water repellency by proxy, whereas the contact angle method more directly measures the degree to which a feather repels water. We consider the contact angle method to also be more standardizable than the structural index, although it requires more sophisticated equipment. We caution against continued use of the structural index and highlight the direct role of uropygial oil in enhancing feather water repellency.