Journal of Avian Biology最新文献

Ecological specialization shapes biodiversity patterns, yet the relative importance of historical, climatic, and biotic drivers of specialization remains debated. We investigated how time since colonization (TSC), climatic stability (decomposed in temperature and precipitation stability), and competition influence ecological specialization across diet, foraging behavior, and habitat dimensions in Emberizoidea bird assemblages globally and across three bioregions (Nearctic, Neotropics, Palearctic). Using phylogenetic data, species distributions, and trait databases, we quantified specialization with the Gini Index and modeled its predictors using spatial autoregressive models. Globally, diet and habitat specialization increased with TSC and competition, while foraging specialization decreased with the same predictors. Regional patterns diverged markedly: in the Nearctic, competition increased foraging specialization, and climatic stability decreased diet and habitat specialization; in the Neotropics, TSC and temperature stability promoted diet specialization, competition enhanced habitat specialization but decreased diet and foraging specialization, while all three factors reduced foraging specialization; in the Palearctic, competition and temperature stability increased diet specialization, while TSC promoted habitat but decreased diet and foraging specialization. These contrasting patterns reveal that ecological specialization emerges from contingent interactions between evolutionary history, climatic stability, and biotic factors rather than universal rules, with different specialization axes responding distinctly to the same drivers across biogeographic contexts.

Portable devices, or biologgers, attached to animals are designed to record data on unobservable aspects of animal behaviour, physiology and ecology. However, wearing such devices is expected to be costly, and researchers must ascertain how such devices influence the behaviour, reproduction and survival of tagged individuals. GPS tracking devices with solar-powered batteries are now available in the 1.6–2.0 g mass range, allowing for long-term, high-resolution spatial data collection in species as small as 32–40 g (assuming a relative device mass ≤ 5% of body mass). In this study, we investigate the impact of wearing GPS devices on adult Kentish plovers Anarhynchus alexandrinus weighing 34–46 g. To assess any potential adverse effects of tagging, we quantified 1) general behaviour with behavioural time-budget assays, 2) detailed incubation behaviour with nest cameras, 3) reproductive outcomes, and 4) apparent survival from non-breeding season resighting rates 4–5 months after initial deployment. In each case, tagged birds were compared with untagged, colour-ringed control group birds. Despite wearing devices of up to 5% of body mass, we found no clear effects of tagging in any aspects of behaviour or life-history that we assessed. Our results collectively support the conclusion that any impacts of tagging on individuals in this study system are negligible and appear unlikely to manifest demographic consequences.

Avian vocal mimicry has typically been examined through the lens of sexual selection acting on males. However, the females of many bird species are accomplished vocal mimics; a fact that cannot be accounted for by traditional male-centric explanations for vocal mimicry. Female superb lyrebirds Menura novaehollandiae mimic primarily during nest defence, whilst male lyrebirds mimic predominantly during sexual advertisement. Here we examined the relationship between female age and vocal mimicry using a dataset of nesting female lyrebirds, several of which were recorded over multiple years. The vocal mimicry produced by females was diverse, and individuals varied greatly in how often they mimicked and what models they mimicked; however, neither the propensity to mimic nor the number of model sounds was explained by female age. Nevertheless, older females were more likely to mimic predators than younger females. There are two main implications of these findings. First, age is unlikely to explain intra-population variation in female mimetic repertoires. Second, females might fine-tune their mimetic repertoires as they age and mimic only models that are most effective during nest defence, such as predators. We discuss what these results mean for our understanding of vocal mimicry and vocal learning in songbirds of both sexes.

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.