Journal of Avian Biology最新文献

Birds can show patterns of sexual size dimorphism as early as the nestling stage. This raises the question of how the faster growing sex might reconcile the energetic and nutritional needs of a faster growth rate with resource allocation to other important life functions, such as the development of innate immune function. Innate immunity represents the main line of defence against diseases, and while some innate immune defences are already present at hatching, substantial development occurs throughout the nestling stage. Hence, this development may compete for resource allocation with growth, potentially affecting nestlings in a sex-specific way in species showing sexual size dimorphism at an early age. However, little is known about how sex might shape life-history strategies early in the life cycle. In this two-year study, we compared size, mass and immune function (hemolysis-hemagglutination assay, bacteria killing assay and haptoglobin assay) between sexes of great tit Parus major nestlings, likely reflecting the outcome of relative resource allocation during ontogeny. To account for variation in environmental quality, we evaluated sex differences in relation to a brood size manipulation and in relation to seasonal progression. We found that male nestlings grew to a larger size at day 14 than their female siblings. However, we also found some indication that males developed a better immune defense than females, albeit their faster growth. Thus, males manage to invest more heavily in both growth rate and immune defence, probably depending on males being dominant to females in the competition for parental feeding, resulting in higher resource acquisition.

Animal-borne trackers are commonly used to study bird movements, including in long-distance migrants such as shorebirds. Selecting a tracker and attachment method can be daunting, and methodological advancements often have been made by trial and error and conveyed by word of mouth. We synthesized tracking outcomes across 2745 dorsally mounted trackers on 37 shorebird species around the world. We evaluated how attachment method, power source, data retrieval method, relative tracker mass, and biological traits affected success, where success was defined as whether or not each tag deployment reached its expected tracking duration (i.e. all aspects succeeded for the intended duration of the study: attachment, tracking, data acquisition, and bird survival). We conducted separate analyses for tag deployments with remote data retrieval (‘remote-upload tag deployments') and those that archived data and had to be recovered (‘archival tag deployments'). Among remote-upload tag deployments, those that were a lighter mass relative to the bird, were beyond their first year of production, transmitted data via satellite, or were attached with a leg-loop harness were most often successful at reaching their expected tracking duration. Archival tag deployments were most successful when applied at breeding areas, or when applied to males in any season. Remote-upload tag deployments with solar power, satellite data retrieval, or leg-loop harnesses continued tracking for longer than those with battery power, other types of data retrieval, or glue attachments. However, the majority of tag deployments failed to reach their expected tracking duration (71% of remote-upload, 83% of archival), which could have been due to tracker failure, attachment failure, or bird mortality. Our findings highlight that many tag deployments may fail to meet the goals of a study if tracking duration is crucial. Using our results, we provide guidelines for selecting a tracker and attachment to improve success at meeting study goals.

Uropygial secretions are thought to play an antimicrobial role in birds, but few studies have compared their effectiveness across multiple species and microorganisms using standardized methods. We evaluated the antimicrobial activity of uropygial secretions from 212 individuals of 11 passerine species in southwestern Spain, testing their inhibitory effects against Bacillus licheniformis, B. subtilis, Candida albicans, Escherichia coli, and Salmonella typhimurium by flow cytometry. Antimicrobial activity varied significantly among species and microorganisms: house sparrows Passer domesticus consistently exhibited stronger and broader responses, whereas activity against S. typhimurium was generally low. Phylogeny, migratory status, and social behavior did not explain variation, but uropygial gland size was positively associated with antimicrobial activity both globally and in some bird species. Body condition exhibited species-specific associations with antimicrobial activity, showing positive correlations in some bird species and negative correlations in others. Overall, our findings highlight the uneven distribution of antimicrobial defenses among passerines and underscore the importance of comparative, chemically informed, and methodologically standardized approaches to clarify the ecological and evolutionary significance of uropygial secretions.

The Asian koel Eudynamys scolopaceus is a generalist brood parasite that exploits a diverse array of host species across Asia. A previous study using avian visual modeling found no evidence that koels had evolved eggs that mimic the eggs of one of their oldest known hosts, the house crow Corvus splendens, or that they had host-specific egg types when parasitizing two other common hosts in Bangladesh. In this study, we used museum collections to compare eggs from three koel subspecies to a broader range of host species from multiple areas across Asia. Our goals were to: 1) determine if koel eggs differed in appearance based on the host species they parasitized, and 2) determine if koel eggs appear similar to the eggs of any of the hosts we measured, which might suggest egg mimicry. We found no evidence that koels have evolved host-specific egg types (all koel eggs were similar in appearance to each other regardless of the host nest) or that koels had evolved egg mimicry with house crows. Rather, koel eggs were the most similar in color to the red-billed blue magpie Urocissa erythrorynhca in all geographic regions and were more similar in pattern to the other parasitized crow hosts than to house crows in the same geographic region. Thus, there is some evidence that koels may have evolved eggs that mimic the eggs of these other hosts, rather than the eggs of the house crow, but further experimentation to test these hosts for egg rejection ability is warranted.

Recent studies have shown that birdsong is not exclusively a male trait. However, despite increasing research intensity, female singing is still rarely reported in temperate migratory species. Here, we report the observation and description of female vocalization in the great reed warbler, Acrocephalus arundinaceus. We analysed vocal expression of individually marked great reed warbler females in two central European populations in Slovakia and the Czech Republic and show that these vocalizations meet criteria for song. We found that 39.5% of nesting females sang from the nest during early incubation within two hours of video recording. Female mating status, locality, day of the season, and male singing activity did not predict song use in this species, but song rates decreased over the breeding period. Based on current and previous observations, we hypothesize that female great reed warblers use song to signal their territorial presence and reproductive status, potentially deterring conspecific female competitors. However, given that this study was done only in one context and moment in the breeding cycle (early incubation), we encourage further investigation of the functions of female song in this and other temperate migratory species whose female song was overlooked in the past.

Ron-Arroyo, N., Mouriño, J., Rodríguez-Silvar, J., Bermejo Díaz de Rábago, A. and Martínez-Abraín, A. 2025. Refuge abandonment in a formerly harvested waterbird and the consequent formation of multi-species bird colonies. – J. Avian Biol. 2025: e03451, https://doi.org/10.1002/jav.03451.

The original article has also been updated to rectify these errors.

Survival is a life history trait that contributes most to population dynamics in long-lived birds, and the study of individual characteristics is relevant for population conservation. Here we provide information on territorial recruitment and individual replacement in a population of Bonelli's eagle Aquila fasciata in southeastern Spain based on a long-term photographic capture–recapture 19-year dataset. We also investigated how individual factors such as sex, age, experience and age at first breeding influence the apparent survival of breeding Bonelli's eagles using Cormack–Jolly–Seber models. An increase in recruitment rates and a decrease in age at first breeding were observed in the breeding population over time. The apparent survival was high and the reproductive dispersal was very low. The improvement in apparent survival was age-related and higher in females (0.90 for non-adults and 0.92 for adults) than males (0.87 for non-adults and 0.89 for adults). These findings can be explained by age-related improvements and differences in movement behaviour between sexes during the breeding season, with females being exposed to lower risks from anthropogenic or natural causes. We also found a positive relationship between territorial experience and the probability of apparent survival, with inexperienced female breeding birds having a higher survival than males. Our results showed that immature breeders had a similar survival to experienced or older birds breeding for the first time, suggesting that age at first reproduction is controlled by reproductive restraint. Our results provide demographic information that improves the understanding of the population dynamics of the long-lived territorial species, and their estimation has important implications for the management and conservation of Bonelli's eagle populations.

Roads are among the most widespread anthropogenic structures, and their presence can impact biodiversity in surrounding landscapes through disturbance and collision risk, particularly when traffic volumes are high. However, the impact of roads with low traffic volumes in open landscapes is much less clear. In the open landscapes of lowland Iceland, road traffic is still relatively low but increasing, and the surrounding landscapes support internationally important populations of several breeding wader species. Here, we used transect counts perpendicular to low-traffic (≤ 15 000 vehicles day⁻¹) roads across the lowlands of southern Iceland to quantify variation in the densities of ground-nesting birds with distance from roads, and to assess how far from the roads any such effects extended. The total abundance of birds increased significantly by 6% per 50 m interval from roads, and densities within 200 m of roads were ~ 20% lower than densities between 200 and 400 m from roads. Four species – whimbrel Numenius phaeopus, golden plover Pluvialis apricaria, dunlin Calidris alpina and meadow pipit Anthus pratensis – were found in significantly lower densities closer to roads, while four – black-tailed godwit Limosa limosa, redshank Tringa totanus, snipe Gallinago gallinago and redwing Turdus iliacus – showed no change with distance from roads. Redwing was found in higher densities, and dunlin in lower densities, surrounding roads with higher traffic volumes. As approximately 20% of lowland Iceland is within 200 m of roads, the impact of roads on the overall abundance of ground-nesting birds could be substantial. The results show that even relatively low-traffic roads can have a significant impact on adjacent wildlife populations. Road construction, along with other anthropogenic structures, has been shown to have negative effects on bird abundance, and identifying areas for protection from such developments may be the most effective approach to reducing human impacts on the internationally important wildlife of lowland Iceland.

Phenotypic plasticity is a major mechanism whereby organisms adjust their traits within-generations to changes in environmental conditions. In the context of range expansions, plasticity is thought to be especially important, as plastic changes in traits can lead to rapid adaptation. One epigenetic process in particular, DNA methylation, enables organisms to adjust gene expression contingent on the environment, which suggests it may play a role in range expansions. At present, we know little about how methylation is regulated in wildlife, especially expression of the enzymes responsible for altering methyl marks on the genome. In this study, we compared expression of three epigenetic regulator genes (DNA methyltransferase 1, DNMT1; DNA methyltransferase 3, DNMT3; and one ten-eleven translocation methylcytosine dioxygenase, TET2) in three tissues (gut, liver, and spleen) of house sparrows Passer domesticus from nine countries. Some countries are in the native range of the species (Israel, the Netherlands, Norway, Spain, and Vietnam) whereas others are sites the species has colonized in the last 150 years (i.e. Australia, Canada, New Zealand, and Senegal). In this exploratory study, we asked whether non-native birds and/or birds from sites with comparatively unpredictable climates would express different levels of these genes. We found that all three genes were expressed more in sparrows from the native range and from areas with more stable temperatures. Expression of all three genes was also strongly correlated among-locations and within-individuals, but mean expression was quite different among tissues. Many factors (e.g. urbanization of the capture site, sex of the bird) did not significantly affect gene expression, but others surprisingly did (e.g. latitude). Our results suggest that these enzymes could be important in range expansions or geographic distribution generally, but more detailed investigations will be insightful.

Biologgers enable real-time collection of detailed behavioural and physiological data from wide-ranging animals, including seabirds inhabiting remote regions. However, the number of studies using tracking devices has not been matched by research exploring the behavioural and fitness costs of deployment, and the effects on data reliability. We assessed how GPS loggers, video loggers, and time depth recorders (TDRs) affect the behaviour, physiology, and reproductive performance of European shags Gulosus aristotelis breeding on Sklinna, Norway. The loggers varied in mass, attachment location and deployment duration, allowing comparison of their relative effects. Birds without loggers served as controls to assess logger-related changes in adult body mass, chick growth, reproductive success, and survival. Birds with longer-term tail-mounted GPS loggers and leg-mounted TDRs showed altered foraging behaviour, including shorter trips and dives, compared to birds with tail-mounted GPS and TDRs of the same weight, instrumented for only two days. A mean loss in body mass was experienced by adult birds regardless of the logger type used, while chick growth rate dropped to 20% of that observed in control nests when video, TDR and GPS loggers (~ 4% of body mass) were deployed together. Logger attachments did not impact reproductive success, and overall logger birds showed higher survival than controls. However, female survival was lower than that of males among birds fitted with video and long-term GPS loggers. Our results demonstrate the importance of measuring behavioural and physiological effects that can scale over time. The advances in our understanding of animal ecology and behaviour generated by biologging have been impressive, but there is a need to consider the impacts on animal welfare and data quality. Consistent reporting of logger deployment details is essential to assess biologging impacts across species and refine protocols that account for device weight, drag and attachment location.