Long-term assessments are essential for understanding whether recent local changes in seabird abundance reflect genuine population recovery or redistribution of wintering birds within a persistently altered system. We analyzed wintering diving seabirds in the Polish Maritime Areas (PMA) of the southern Baltic Sea by combining historical baseline data from 1990 to 1993 with national survey data from 2005 and standardized monitoring from 2011 to 2025. Assemblage-level analyses covered 21 common diving species, including 9 benthic-feeding and 12 fish-feeding species. Species-level analyses focused on six representative species: Long-Tailed Duck (Clangula hyemalis), Velvet Scoter (Melanitta fusca), Common Scoter (Melanitta nigra), Greater Scaup (Aythya marila), Great Cormorant (Phalacrocorax carbo), and Black Guillemot (Cepphus grylle). We assessed long-term changes in abundance, compared patterns between feeding groups, examined species-specific trajectories, and evaluated the changing importance of the study area for biogeographic populations. The abundance of the wintering diving seabird assemblage was approximately 40
Understanding how ecologically similar species coexist in shared environments is a central question in community ecology, especially where closely related species breed sympatrically and exploit overlapping resources. Marsh terns of the genus Chlidonias provide an excellent model for examining fine-scale niche differentiation, yet comparative data on diet and foraging habitat use in sympatric populations remain scarce. We examined whether White-winged Tern Chlidonias leucopterus and Black Tern Chlidonias niger breeding sympatrically in the near-natural Bug River valley (eastern Poland) differ in chick provisioning diet and adult foraging habitat use. Chick provisioning was quantified from video recordings at nests, and adult foraging behaviour was assessed using transect scans near mixed colonies. Overall chick provisioning diet did not differ significantly between species, indicating broad dietary overlap at the multivariate level. However, taxon-specific analyses suggested directional tendencies, with White-winged Terns tending to deliver more terrestrial prey, particularly Orthoptera, and Black Terns tending to provide more fish. Brood size also influenced diet composition, suggesting that provisioning patterns varied with brood demand. In contrast, adult foraging habitat use differed strongly between species: White-winged Terns foraged mainly over meadows, whereas Black Terns used river channels more frequently. Thus, niche differentiation was most evident in foraging habitat use, whereas trophic differentiation in chick provisioning was weaker and taxon-specific. Such partial, multidimensional niche partitioning may reduce interspecific competition and facilitate coexistence in mixed colonies. Our results highlight the importance of behavioural differentiation in sympatric consumers in heterogeneous wetland landscapes.
Understanding species’ nest site selection is essential for successful species conservation, because it allows to identify critical areas, allocate resources efficiently, and formulate effective measures. One indirect way to assess this for migratory birds is by examining breeding timing, considering that higher-quality habitats are occupied earlier, while controlling for extrinsic and intrinsic factors. However, how site- and individual-level factors jointly correlate with the nest site selection remains unclear. This study examined the population of Northern Wheatears (Oenanthe oenanthe), a long-distance migratory songbird, nesting in burrows from introduced rabbits on the German island Norderney. Using data from 321 nests monitored between 2021 and 2025, we assessed the influence of nest site- (habitat type, longitude, distance to paths, and streets) and individual-level (male age) characteristics on hatching date. We found a longitudinal gradient in hatching dates of the juveniles in white dunes, with earlier hatching in the east of the island, where rabbit density is highest, as shown in previous studies. In grey and vegetated dunes, hatching dates were primarily influenced by the age of the males, with chicks of older males hatching earlier. Habitat type and distance to paths and streets had no significant effect. These findings suggest a different timing of nesting related site- and individual-level characteristics. Habitat areas of the Wadden Sea National Park with short vegetation and rabbit burrow availability are critical breeding sites for Northern Wheatears on the island. Conserving natural habitats, maintaining rabbit population, and not expanding anthropogenic grassland areas are key actions to sustaining suitable habitat conditions for the Northern Wheatear population.
Birds use song to communicate in multiple contexts, including territoriality and courtship. Of particular interest is the phenomenon of song sharing, in which direct neighbors’ songs are more similar to one another than those of non-direct neighbors. Song sharing has been studied extensively in oscine songbirds. However, despite the high diversity of hummingbird vocalizations, less attention has been given to this lineage. Anna’s Hummingbird (Calypte anna) has a spectrally complex, three-phrase multisyllabic song that varies on both macrogeographic and microgeographic scales. In this study we tested for song sharing between neighbors and for an effect of physical distance on song distance within a single population. In January and February of 2021, we audio recorded 29 Anna’s Hummingbirds in Golden Gate Park, San Francisco, CA. We characterized syllable types, and measured spectral and temporal features of songs in Raven Pro 1.6. We evaluated how Anna’s Hummingbird song form may change over time by comparing our results to those of a study conducted at the same site in 1999 and recordings from the 1980s. In our recordings from 2021, we identified 25 syllable types and eleven song types, and found evidence for both syllable and song type sharing between males with adjacent territories. We found high turnover of syllable types between the 1980’s and 2021, demonstrating the potential for rapid cultural evolution in hummingbird song.
Conservation areas (CAs) are critical tools in biodiversity conservation, yet their relationship to species of highest conservation need (i.e., species that are rare, range-restricted, sensitive to habitat change, or under significant threat) and the habitats they depend on is understudied. We apply a dynamic occupancy modeling framework to point count data from surveys both in and outside of Canadian Intermountain Joint Venture (CIJV) and Pacific Birds Habitat Joint Venture (PBHJV) CAs in British Columbia (BC), Canada and data from the BC Marsh Monitoring Program from 2021 to 2024, asking whether sites within CAs contain greater proportions of priority habitat compared to sites in adjacent unprotected areas, and thus promote the occupancy of conservation priority birds. We uncovered strong relationships between priority bird occupancy and environmental conditions, but little difference in most priority habitat proportions between sites in CAs and unprotected areas. We only detected a relationship between a site’s conservation status and priority bird occupancy in two of ten priority bird groups. Aerial insectivores and species at risk act-listed birds in CIJV showed reduced site extinction probability in CA sites, perhaps due to greater foraging opportunities from the more prevalent wetland habitat. Using insights gained from our models, we make recommendations for conservation practitioners looking to ensure CAs can better benefit bird species with the greatest need. Our results contribute to the broader understanding of the role CAs play in biodiversity conservation, and suggest that they require special attention to effectively preserve priority species.
Purple Martins (Progne subis) are long-distance migratory, aerial insectivores facing population declines, yet critical gaps remain in our understanding of the full annual cycle for all recognized subspecies. Whereas the migratory routes of the eastern (P. s. subis) and western (P. s. arboricola) subspecies have been documented, the Desert Purple Martin (P. s. hesperia) migratory pathway remains unknown. This study presents the first migratory records for the Desert Purple Martin, providing insights into its migratory phenology, stopover ecology, and nonbreeding range. During the 2022 and 2024 breeding seasons in Arizona, USA, we captured and equipped eleven individuals with light-level geolocators and satellite transmitters. Here, we report the migratory movements for three individuals. Two individuals migrated approximately 9000 km to the São Francisco Basin, occupying a nonbreeding region in northeastern Brazil that is spatially segregated from those reported for the other subspecies. The southbound migration was prolonged (ca. 60 days, SD ± 5) and featured multiple stopovers, particularly an extended around a 35 days (SD ± 1) stopover in western Mexico; the northbound migration was accelerated (20 days, SD ± 7). These data suggest that the desert subspecies may be geographically isolated from eastern and western lineages on its nonbreeding grounds, with its nonbreeding range centered in the semi-arid Caatinga and Cerrado biomes, regions increasingly threatened by agricultural conversion. Our findings provide essential baseline movement, habitat use, and phenological data for the Desert Purple Martin and underscore the need for subspecies-specific conservation strategies that address threats across the annual cycle.
Tracking technologies have revolutionized the study of bird migration, offering unparalleled insights into ecology, behaviours and flyways. However, due to the typically small proportion of individuals tracked, their reliability for estimating population-level migratory parameters, particularly temporal aspects, remains poorly understood. Although this uncertainty is acceptable in behavioural or ecological studies, scaling up from individuals to populations to infer migratory timing (i.e., onset or end) has critical implications for management and conservation. For example, in the European Union, accurately identifying migration onset is essential for setting harvesting calendars for huntable species. Using Eleonora’s Falcon (Falco eleonorae) as a simplified study system, we GPS-tracked approximately 7
Headstarting is increasingly used as a conservation intervention for the Eurasian Curlew (Numenius arquata), yet evidence on the early post-release movement ecology of captive-reared juveniles remains limited. We analysed the post-release ranging behaviour of headstarted curlews using GPS tracking data collected over 5 years, from 2017 to 2021, in Poland. A total of 62 individuals were tagged, of which 34 were included in analyses of post-release movements, including 20 individuals that provided GPS tracks covering the entire pre-migration period and were therefore used for home-range analyses. On average, birds departed on autumn migration 28.9 ± 9.7 (mean ± SD) days after release, and no relationship was found between release date and departure timing. During the pre-migration period, the mean home-range size estimated using kernel density estimation was 188.6 ± 96.1 ha, based on the 90
Keratinous and bony tissues preserve ecological information, yet conventional isotope methods often lack the spatial resolution to detect fine-scale dietary or habitat transitions. Here, we present a high-resolution framework using laser ablation isotope ratio mass spectrometry (LA-IRMS) to reconstruct stable carbon isotope (δ13C) chronologies in feathers, claws, bills, and cranial bones across three avian species. LA-IRMS measurements showed strong agreement with those from conventional elemental analyzers of identical feather sections, supporting the reliability of the method for high-resolution isotope profiling. We illustrate this with three case studies that highlight the ability of LA-IRMS to resolve δ13C variation in archived and experimental samples. Each study comprises a single individual and serves as a methodological demonstration rather than a population-level analysis. Using 200 and 300 µm laser spacing, this minimally destructive technique achieves sub-millimeter resolution, capturing isotopic variation from near-hourly to multi-month temporal scales. In European Greenfinch, a controlled diet-shift experiment revealed clear δ13C transition between the original feather and its replacement. In a specimen of Marsh Warbler, δ13C values along the bill contour indicated enrichment over approximately 6 months of growth, while cranial bone reflected long-term isotopic averaging and region-specific variations. Archived Osprey claw exhibited prolonged foraging in tropical C₄-dominated habitats followed by a sharp δ13C decline near the base. These case studies demonstrate that avian keratinous tissues function as sequential archives of individual ecological history, with bone mostly reflecting integrated long-term inputs. LA-IRMS enables non-destructive, temporally explicit isotope reconstruction from archived tissues and expands opportunities for fine-scale ecological and physiological inference.
Flight in birds is supported by the presence of wing feathers known as remiges. Particularly, the asymmetrically shaped primary feathers (Remiges primarii) generate the necessary lift that allows a bird to take off. These feathers are supplemented with keratinous microstructures called hooklets. The interlocking ability with the opposing posterior barbules creates a continuous surface referred to as the feather’s vane. Using scanning electron microscopy of individual barbs, this study provides a detailed characterization of hooklet distribution within a primary wing feather of the Common Wood Pigeon (Columba palumbus; Columbidae). The results of this study reveal gradients in the distribution of hooklets within the feather vane that are discussed in the context of the physical forces to which a feather is exposed to during flight. Furthermore, the study reveals a greater variation in the number of hooklets per barbule than previously described, indicating that the sole use of the number of hooklets per barbule as a potential taxonomic marker is very limited.
Moult in birds is a highly energetically expensive process. Therefore, feather replacement in most species does not coincide with breeding or migration periods. However, when time constraints prevent completion before migration, many birds suspend feather replacement and resume it post-migration. One species exhibiting active primary moult during migration is a small wader–the Dunlin (Calidris alpina). Despite being one of the most extensively studied of their group in the western Palearctic, some aspects of its biology, such as primary moult suspension and factors influencing it, remain poorly understood. We investigated the occurrence and determinants of primary moult suspension in Dunlins during autumn migration along the Gulf of Gdańsk coast between 1985 and 2023. Our results revealed that only a small proportion (14
Migratory birds that arrive early to their breeding sites occupy higher quality habitat, secure preferred mates, and may gain fitness advantages. It is widely assumed that arrival date is subject to natural selection, and thus localities where montane breeding birds arrive earliest may be most optimal, representing a tradeoff between abiotic limitations (e.g., climate) at higher elevations, and biotic factors (e.g., predators, food, nesting sites) at lower elevations. We used autonomous recording units to determine apparent territory establishment date (hereafter ‘established territory’) of Swainson’s Thrush (Catharus ustulatus) across an elevational gradient within the White Mountains, New Hampshire. Thrushes apparently established territories at high elevations (1200 m) 6.6 days earlier than at lower elevations (250 m). Additionally, we explored the role of mean growing season temperature, aspect, and annual variability (year) to territory establishment. Annual variability was the only covariate that demonstrated statistical support where territory established in thrushes was about two days earlier in 2020 versus 2019 and 2021. We suspect this delay may be explained by variation elsewhere in the annual cycle, as we did not observe differences in general climatic conditions (snow depth, precipitation, temperature). We found support suggesting Swainson’s Thrush establishes breeding territory earlier at high elevations perhaps due to the strong association between spruce-fir forests and high elevation, which is likely due to preference for this vegetation type. Montane ecosystems are at risk when considering the changing climate, and warming temperatures may threaten the vegetation that sensitive breeding birds rely on.
Avian malaria, caused by Plasmodium parasites, commonly persists as a chronic infection, yet reliable treatment protocols remain insufficiently evaluated. Assessing treatment efficacy is essential for improving disease management and understanding impacts on host health. We conducted a 2.5-year experimental study to assess the efficacy and safety of atovaquone-proguanil (Malarone®) against Plasmodium relictum (genetic lineage pSGS1) in canaries (Serinus canaria domestica). Seventy-six birds were assigned to four groups: experimentally infected and treated (E1), infected and untreated (E2), uninfected and treated (C1), and uninfected and untreated controls (C2). Following blood inoculation, birds in groups E1 and C1 received four treatment cycles over two months. Parasitemia was monitored by microscopy and PCR for 981 days, and survival, body mass, and biochemical parameters were assessed to evaluate long-term effects. We hypothesized that Malarone would clear blood stages, but that recrudescence might occur due to persistent exo-erythrocytic stages.Malarone treatment resulted in rapid elimination of parasitemia in E1 birds, with no relapses detected by microscopy or PCR during follow-up. In contrast, untreated infected birds exhibited persistent low-level and recurrent parasitemias. Survival did not differ among groups, and most physiological parameters remained within reference ranges. Transient increases in total protein and creatine kinase occurred only in untreated infected birds, indicating limited physiological impact of chronic infection and no detectable long-term toxicity of the treatment. Our results demonstrate complete and sustained clearance of P. relictum (pSGS1) following prolonged Malarone treatment. The absence of relapse suggests limited exo-erythrocytic persistence or effective suppression, supporting the safe and effective use of this drug for avian malaria.
Avian haemosporidians are common vector-transmitted parasites that infect birds. Although avian haemosporidians have been studied extensively in songbirds, less is known about haemosporidian prevalence in raptors, particularly in the United States. We used molecular methods to test blood samples collected from raptors at five wildlife rehabilitation centers across the United States for avian haemosporidians. We identified parasites from the genera Haemoproteus, Leucocytozoon, and Plasmodium using a multiplex PCR and determined prevalence by raptor host species and site. Almost half of the raptors tested (47
In species with obligate bi-parental care, investment by both parents in a current reproductive bout is critical to offspring growth and survival. The degree to which an individual can invest in their offspring relies on their quality as a parent. Parental quality can be communicated between individuals in a mated pair via ornamental features, as they may honestly reflect aspects of direct or indirect investment in offspring. In this study, we investigated whether the yellow-orange fleshy integuments of Atlantic Puffins Fratercula arctica reflect parental quality, as approximated by offspring hatch date and growth metrics. No aspect of parental coloration predicted hatch date, but several metrics of maternal and paternal coloration predicted offspring mass growth, peak mass and normalized wing growth. We also explored whether hatch date influenced patterns of chick growth and found that timing (before or after the arrival of the main food source) significantly predicted mass and skeletal growth. Specifically, early hatching chicks achieved higher peak masses but exhibited reduced wing growth, potentially reflecting alternative strategies between investing primarily in weight gain or structural development. Together, these results highlight chick growth as a complex feature associated with both breeding phenology and parental phenotype.
Migratory routes align with leading lines where favorable soaring conditions occur. Soaring raptors, including the Lesser Spotted Eagle (Clanga pomarina), avoid large water bodies and mountain ranges where conditions are less conductive to sustained soaring flight, resulting in mass migrations through migratory bottlenecks. Lesser Spotted Eagles breed in Central and Eastern Europe and parts of Asia, overwintering in southern Africa. Nearly the entire global population follows a narrow 5360 km flyway from the Middle East to southern Africa. Since 1994, 42 adult eagles were tracked using a range of telemetry technologies. Here, we leverage these tracking data and reveal that Lake Tanganyika forms a major migratory barrier for the species. All tagged eagles passed through a narrow, c. 8-km-wide bottleneck at the lake’s southern tip, near the Tanzania-Zambia border. This route adds a detour of up to 500 km, particularly for individuals wintering in Angola. High-resolution GPS-GSM telemetry enabled the visualisation of the routes navigated by four adult eagles between 2012 and 2016 as they passed through the narrow migratory bottleneck. On their return northward migration, eagles pass Lake Tanganyika over a much broader front. This study provides the first documentation of the “Lake Tanganyika Bottleneck” for this species. The bottleneck’s existence is likely driven by a combination of topography, habitat, and climatic conditions. Given our findings, we call for regional ornithologists to conduct standardized migration counts at the site to assess its significance for other migratory soaring birds. Migratory bottlenecks offer a vital natural stage for public engagement activities and capacity building for conservation initiatives within the region.
Haemosporidian parasites can alter host immune and physiological condition, yet their hematological effects may depend on habitat disturbance and seasonality. We investigated how haemosporidian infection relates to hematological parameters of common understory birds across a land use gradient in tropical montane cloud forests of central Veracruz, Mexico. During 2013–2014, we sampled six abundant passerines across five land use types (conserved forest, peri-urban forest, urban forest, shade coffee plantation, and cattle field). Infections were assessed by microscopy and PCR, and hematological parameters (differential leukocyte proportions, H/L ratio, total leukocytes, thrombocytes, and polychromatophils) were analyzed with generalized linear mixed models using total haemosporidian abundance (parasites per 10,000 erythrocytes) as the primary infection predictor; genus-specific analyses (Plasmodium vs Haemoproteus) were used as secondary complements where sample sizes allowed. Overall infection prevalence was 61
Avian blood parasites are vector-transmitted protozoan parasites and common in wild birds. They cause acute and chronic infections at different life stages with potentially detrimental effects on host fitness. Transmission often happens during the nestling period, when biting dipterans have easy access to featherless skin. However, little is known about patterns of infection within and between broods. Therefore, we investigated prevalence of haemosporidians (Leucocytozoon, Plasmodium and Haemoproteus) in Jackdaw (Corvus monedula) nestlings over four non-consecutive years. Prevalence varied by year, averaged at 33.9
Sexual dimorphism in birds is frequently expressed through plumage traits. Yet, the extent to which males and females also differ acoustically remains poorly understood in many Neotropical passerines. In antbirds (Thamnophilidae), several species exhibit pronounced plumage dimorphism, but whether these visual differences are accompanied by consistent vocal divergence is still unclear. This gap limits our understanding of how different signaling modalities evolve under sexual and social selection in suboscine birds. Here, we evaluated sexual differences in vocal behavior in four Cerrado antbird species (Thamnophilus doliatus, T. pelzelni, Herpsilochmus atricapillus, and H. longirostris). We employed a comparative framework combining traditional bioacoustic measurements, mel-frequency cepstral coefficients, and deep learning-based BirdNET embeddings. We evaluated sex differences through multivariate analyses, linear mixed effects models, and supervised classification approaches. Across species and analytical methods, male and female vocalizations showed extensive overlap, and classification performance was generally low and only modestly above chance. However, the strength of differentiation varied among species, with T. pelzelni showing the clearest evidence of subtle sex-related divergence. Together, our results indicate that vocal sexual dimorphism in these Cerrado antbirds is generally weak and inconsistent, contrasting with the pronounced plumage dimorphism observed in the same taxa. These findings suggest that sexual differentiation may be expressed unevenly across communication modalities, with stronger divergence in visual than acoustic traits. More broadly, our study highlights the importance of integrating traditional and machine learning-based approaches to investigate subtle variation in animal communication and provides a framework for studying multimodal sexual dimorphism in suboscine birds.
