Birds

Exploratory behavior involves gathering information and reflects how individuals interact with their environments. In seasonal environments, individuals undergo environmental cycles that might lead to differences in this behavior between locations and seasons. Here, we compare the exploratory behavior measured during an open-field test in 102 adult individuals of rufous-collared sparrow (Zonotrichia capensis) from three locations in central and southern Chile. A generalized mixed-effect model (GMM) was utilized to compare the exploratory behavior between locations and seasons. The two-way interaction between both variates was also included. Body mass and sex were included as covariates and elevation of the study sites as a random effect. The result indicates that exploratory behavior significantly varied between populations and seasons. Specifically, birds tested in the Chilean central zone (33° S) and breeding birds showed higher exploration scores during the open-field test than birds tested in the southern zone (38° S) and non-breeding birds. These findings suggest that exploratory behavior may be driven by local environmental pressures, underscoring the role of weather and seasonality in shaping this behavior. Full article

The flock formation of bird species is a crucial behavioral process that enables them to colonize urban areas. However, the factors influencing the structure and composition of ground-feeding bird flocks have not yet been analyzed. This study aimed to relate flock characteristics, including size, number, species richness, and composition, to local and landscape factors in the urban parks of Buenos Aires City, Argentina. Surveys of flocks were conducted in 16 parks during the breeding season, covering both mono-specific and mixed-species flocks. Flock numbers were positively correlated with tree, lawn, and bare ground cover but negatively associated with raptor presence in the parks. Flock species richness declined with increased noise and pedestrian traffic but rose in parks where raptors were present. The composition of species in flocks was linked to tree cover, noise, and the presence of raptors. While the Rock Dove (Columba livia) and the Rufous-bellied Thrush (Turdus rufiventris) were more abundant in parks with greater tree cover, the Eared Dove (Zenaida auriculata) and the Monk Parakeet (Myiopsitta monachus) showed increased abundance in more open parks. Zenaida auriculata and Columba livia experienced a decline in abundance in parks where raptors were present. Our findings indicate that resource availability and predation risk are crucial factors shaping flock formation in urban parks. Full article

Urbanization changes the environment through physical constructions, disturbances, and altered resource availability. These modifications influence both prey and predator assemblages. Several studies have indicated that hole-nesting birds outnumber ground nesters in cities. Differential nest predation can be one reason behind this observation. We conducted a multi-year artificial nest predation experiment along an urban gradient by using artificial ground nests and nestboxes in Rovaniemi, Finland. Because visually searching avian predators dominate in cities, we predicted that nest predation of ground nests will increase with urbanization, whereas nests in holes will be better protected than ground nests. Ground nest predation increased with urbanization, being lowest in forest and rural areas, intermediate in suburban area and highest in urban area. However, there was no year-effects on artificial ground nest predation, suggesting that even a single-year results of artificial nest predation experiment can be reliable. In the city, ground nest predation was greater than nestbox predation. In forests, nestbox predation was greater than ground nest predation. Among ground nests, predation was greater in the city than in forests. Among nestboxes, predation was greater in forest than in urban or suburban habitats. Only the ground nest predation was greater in managed than in un-managed parks. Ground nest predation decreased with tree cover and increased with the patch area. No variables were entered in the models of the nestboxes. The results indicated that ground nesters might avoid urban areas as nesting sites. We assume that visually searching avian predators benefit from the lack of covering vegetation in city parks. However, because most avian nest predators, like corvids, are not effective nest predators of hole-nesting birds, urban areas are safe nesting areas for hole-nesters. The results suggest that nest predation is one important factor that could explain, why hole-nesting bird species outnumbered ground-nesting species in cities. The result give support for the hypothesis that nest predation pressure can modify urban bird assemblage structure. Full article

Our study investigates predation among sympatric owl species in the Judea Region, specifically focusing on the predation by Eurasian Eagle Owls (Bubo bubo) on smaller owl species. Field observations conducted between 2006 and 2009 revealed recurrent predation events, with 172 individuals documented as preyed upon by Eurasian Eagle Owls. These results align with previous studies, demonstrating the role of larger owl species as intraguild predators that affect the survival and reproduction of smaller owls. Our findings emphasize the need for further research on intraguild predation and its ecological consequences. This study contributes to a broader understanding of the complex interactions within nocturnal raptor communities and underscores the importance of incorporating such dynamics into conservation strategies to safeguard owl biodiversity in fragmented landscapes. Full article

Anseriformes represent a basal order in the phylogeny of neognath birds and are of particular interest in cytogenetic research due to their distinctive chromosomal features. However, aspects of their chromosomal evolution, such as the distribution and organization of microsatellite sequences, remain poorly understood. Given the role of these dynamic repetitive sequences in chromosome organization, differentiation, and evolution, we analyzed microsatellite distribution in three Anatidae species, each representing a different subfamily: Amazonetta brasiliensis-Brazilian Teal (Anatinae), Coscoroba coscoroba-Coscoroba Swan (Anserinae), and Dendrocygna viduata-White-faced Whistling Duck (Dendrocygninae). This is the first karyotypic description for White-faced Whistling Duck (2n = 78) and Brazilian Teal (2n = 80), whereas Coscoroba Swan, previously analyzed, exhibits a notably high diploid number (2n = 98). Despite sharing a similar macrochromosome morphology, the three showed differences in diploid numbers and microsatellite distribution. Extensive microsatellite accumulation was found in both autosomal and sex chromosomes (Z and W) of Brazilian Teal and Coscoroba Swan, while White-faced Whistling Duck displays minimal hybridization signals and an absence of microsatellites on the sex chromosomes. The accumulation of specific microsatellites, such as (CAC)₁₀ and (GAG)₁₀, in centromeric and pericentromeric regions suggests an association with transposable elements, potentially driving chromosomal evolution. Notably, the substantial accumulation of these sequences on the Z and W chromosomes of Brazilian Teal and Coscoroba Swan, but not White-faced Whistling Duck, supports the hypothesis that repetitive sequence expansion occurs in a species-specific manner, contributing to sex chromosome differentiation. These findings highlight microsatellite mapping as a valuable tool for understanding chromosomal evolution and genomic differentiation in Anseriformes. Full article

Prescribed fires are a management strategy involving the controlled application of fire to achieve specific ecological objectives. In the pine–oak forests in west-central Mexico, we conducted an experimental low-severity prescribed fire to assess its effects on hummingbird diversity. We hypothesized that low-severity prescribed fire would enhance both taxonomic and functional diversity by modifying understory vegetation structure and increasing floral resource availability. To test this, we performed point count censuses in both low-severity prescribed fire and fire-suppressed sites where wildfire had been excluded for over 40 years. Taxonomic diversity was assessed using Hill numbers to estimate true diversity across different abundance weights, while functional diversity was evaluated through indices such as functional richness, functional evenness, and functional divergence. Our results indicated that low-severity prescribed fires did not affect overall hummingbird diversity as both low-severity prescribed fire sites and fire-suppressed sites exhibited comparable species richness. However, sites with low-severity prescribed fire and concave summits showed a significantly higher abundance of common and highly abundant species. Notably, species richness did not align with functional richness, as the fire-suppressed site exhibited the highest functional diversity. These findings suggest that hummingbird community structure is influenced by a combination of fire history, topography, vegetation structure, and floral resource availability. We recommend maintaining a heterogeneous forest matrix, incorporating patches with fire suppression, and areas subjected to prescribed fires of varying severity. This multifaceted approach enhances both taxonomic and functional biodiversity, promoting habitat heterogeneity and ensuring the persistence of diverse hummingbird assemblages in fire-prone ecosystems. Full article

Habitat loss, pollution, and climate change have a global impact on bird diversity, particularly in central Mexico, where human disturbances and unplanned urbanization can lead to the decline of this faunal group. In this study, the effects of season (rainy, warm–dry, or cool–dry) and environmental variables (size, perimeter, vegetation cover, built cover, distance to nearby greenspaces and distance to the closet natural vegetation patch) on the avian diversity at different sites located in a peri-urban landscape in the Metropolitan Area of Mexico City were determined. The study was conducted using the linear transect method to assess the diversity and composition of bird communities from November 2019 to March 2022, recording 290 total bird species. Zumpango Lagoon was the study site with the highest diversity (N = 209, H′  =  3.22) and evenness index (J′  =  0.76). Linear mixed models were used to determine the effects of season and environmental variables of the study sites on the avian diversity. The effect of distance to the nearest greenspace was significantly more positive during the rainy season than the two dry seasons. An ANOSIM test also showed that the avian community associated with water bodies differed significantly from the other communities (R = 0.16, p < 0.001). Despite some anthropogenic activities and human intrusion, sites with water bodies retain a high diversity of birds. This finding indicates the need for immediate conservation efforts to protect many resident breeding species and wintering migratory birds in the study area. Full article

Due to continuing worldwide urban expansion, research into how urban environments affect local flora/fauna has grown significantly. Studies on the impacts of urbanization on birds have explored a wide variety of behaviors (e.g., foraging, breeding, migratory), but there is little research on the impacts of cities on avian coloniality. Various urban-environmental factors may impact colonial birds. The predominance of impervious surfaces in cities, for example, has been associated with the decline of several bird species due to negative effects on availability and quality of habitat. The urban heat island effect and shifts in resource availability (e.g., food, water) may also affect colonial birds. Here, we used five years of community-science data available in eBird to investigate urban impacts on group size in Cliff Swallows (Petrochelidon pyrrhonota), an abundant colonial bird species that now breeds readily under bridges and other built structures over or near water in Phoenix, Arizona, USA. We hypothesized that, based on the colonial breeding habits of these neotropical migratory birds in this desert environment, swallows in Phoenix would form larger groups in areas with more food and water sources and with more built structures. In fact, we found that proximity to water sources and cropland, but not impervious surface density, was positively and significantly related to group size. These results suggest that, in this desert ecosystem, an abundance of food/water resources provided by humans permits Cliff Swallows to form larger social groups during breeding. Although many studies show harmful impacts of cities on local wildlife, our findings highlight how urban and/or agricultural ‘oases’ may relieve some native species from natural resource limitations and permit them to thrive and increase in group size in human-impacted environments. Full article

Limited research exists on the breeding ecology of the black francolin (Francolinus francolinus) in northern Pakistan. This study assessed egg dimensions, clutch size, hatching, fledging, and overall breeding success across different habitats and nests (n = 25) at Totali Game Reserve, Buner. Generalized linear models (GLMs) were used to analyze the effects of nest site characteristics and nest traits on breeding parameters. Egg dimensions were consistent across sites whereas bush nests had slightly wider eggs. The average clutch size was 5.9 ± 1.7 eggs, with an average of 4.8 ± 1.0 hatchlings per nest. A total of 111 chicks fledged, averaging 4.4 ± 1.0 per nest, yielding an overall breeding success rate of 75.5%. Nests containing six eggs had higher hatching success (76.6%). GLMs results showed a significant positive relationship between clutch size and hatchling, while nest site and traits had no significant effects. However, fledgling success was positively influenced by hatchling numbers, with nests in wetland habitats yielding significantly more fledglings (4.6 ± 0.9) than those from dryland habitats (4.0 ± 1.2). These findings suggest Black Francolins prefer nesting in wetland areas in bushes, likely due to better protection and favorable conditions. Full article

While the formation flight of birds offers numerous benefits, such as reduced predation risk, improved orientation, and enhanced communication, the aerodynamic interactions between birds are not fully understood due to their inherent complexity. This study explores the wake vortex dynamics of two flying birds and their influence on aerodynamic forces, based on their relative positions in a group. Using a computational finite volume method, the 3D vortex patterns in the wake of Canada Geese (Branta canadensis) flying at 1000 m altitude and 13.9 m/s airspeed were modeled. The results reveal a complex, undulating vortex structure shaped by the wingbeat amplitude and frequency. The analysis shows that trailing birds positioning their wingtips within the upwash region of vortices that are generated by a leading bird significantly reduce drag and enhance lift, achieving up to a 32% improvement in aerodynamic efficiency, calculated as the lift-to-drag ratio. An optimal separation distance of approximately one wavelength (3.47 m) between birds has been identified, leading to a 7% reduction in both mean drag force and aerodynamic power requirements. These findings, extrapolated to larger bird groups, offer valuable insights into the organization and optimal positioning of birds flying in V-formations, advancing our understanding of collective flight dynamics. Full article

Despite increasing conservation efforts for shorebirds, there are widespread declines in many shorebird species in North America. Climate change is causing significant shorebird range shifts and population declines. This study investigates the relationship between meteorological variability and shorebird population dynamics over ten years (2014–2023) at Fish Haul Beach, Hilton Head Island, South Carolina, USA. Shorebirds, reliant on specific habitats for breeding and foraging, are increasingly vulnerable to climate-driven changes, including shifts in temperature, precipitation, and wind speed. Using Generalized Additive Models with Poisson distribution, we analyzed species-specific count data for 12 shorebird species in relation to annual meteorological variables. Additionally, the Mann–Kendall test and Sen’s slope were employed to assess decadal trends in population counts. The results reveal significant declines in Black-bellied Plover (Pluvialis squatarola), Marbled Godwit (Limosa fedoa), and Willet (Tringa semipalmata). In contrast, Semipalmated Plover (Charadrius semipalmatus) and Piping Plover (Charadrius melodus) showed increasing trends, indicating potential habitat benefits or conservation success. Temperature emerged as a key driver affecting the abundance of several species, while precipitation and wind speed also played crucial roles in shaping population dynamics. Our findings underscore the sensitivity of shorebird populations to weather fluctuations, emphasizing the need for integrating meteorological variability into management strategies to ensure shorebird conservation. This study provides critical insights into the impacts of meteorological variables on migratory shorebird populations along the Atlantic Flyway. It highlights the importance of maintaining healthy coastal ecosystems in South Carolina. Full article

Anthropogenic structures such as overhead powerlines pose potentially high collision risks to flying animals, particularly birds, leading to millions of fatalities each year. Studies of bird collisions with powerlines to date, however, have estimated different numbers of collision per year and per kilometer in highly variable landscapes. This study aimed to clarify the risk of bird collisions with powerlines in an average landscape, to overcome the bias towards studies in collision hotspots. We conducted experiments to determine searcher efficiency, removal, and decomposition rates of collided birds as well as searching for collision victims and recording flight movements and flight reactions towards the powerlines. Annual bird-strike rates and flight phenology were analyzed using generalized additive models (GAMs). We estimated 50.1 collision victims per powerline kilometer per year and demonstrated that pigeons (especially Wood Pigeon, Columba palumbus) accounted for the largest proportion of collision victims (approximately 65%). Our study thus offers the opportunity to estimate the number of bird collisions (and the range of species) that can be expected in areas that are not particularly rich in bird life or sensitive, especially in view of the planned intensive expansion of energy structures in the context of the green energy transition. Full article

Many birds regard partitioning feeding and breeding resources as a strategy to escape competition and co-occurring breeding species. During the breeding season, breeding requirements are essential, yet the patterns and drivers of segregation between and within populations are poorly understood. We monitored the habitat use and chronology of the four co-occurring passerines Eurasian Blackbird, European Greenfinch, Common Chaffinch, and European Serin to examine levels of habitat partitioning and success rates during the breeding season. We recorded nesting sites, nest supports, nest placement, breeding chronology, and productivity in four olive orchards in Fez, central Morocco, from March to August 2018–2019. Our results showed substantial spatial segregation in nesting sites, nest supports, and tree vertical placements. Breeding birds showed significant temporal segregation during the nesting, laying, and hatching phases. These findings suggest distinct spatial and temporal differences in habitat selection among co-occurring passerines, which are suggested to increase avoidance of intra and interspecific competition for resources. Breeding success was very high in European Serin and Eurasian Blackbird. Failure factors were recorded: eggs of European Serin were threatened principally by desertion, abortion, and destruction, and eggs of European Greenfinch were impacted by poaching by children. Our findings provide the first data on the spatial and temporal partitioning of breeding resources among passerines species in Northwest African and probably Mediterranean agroecosystems. Full article

Several researchers have tried to find relationships between acoustic indices and vocal animal communities to use acoustic indices as a passive monitoring method, as human-derived surveys are expensive, time-consuming, and suffer from observer bias. However, supplanting manual surveys with acoustic indices is a daunting task, considering effective indices for biological monitoring need to differentiate biologically relevant sounds from the broader soundscape, including anthropophony and geophony. The objective of our study was to test how well acoustic indices can be applied to avian community monitoring within a temperate grassland ecosystem in North America. We collected avian community data and calculated six commonly used acoustic indices from recordings in an intact lowland tallgrass prairie in the Central Platte River Valley of Nebraska throughout the avian breeding seasons of 2019–2021. Singular acoustic indices had only weak correlations with all community metrics. However, multivariate models including multiple acoustic indices showed potential for monitoring grassland bird abundance when anthropophony was considered. Fragmented grassland remnants likely experience significant anthropophony that needs to be accounted for when monitoring avian populations. Additionally, multivariate models incorporating several indices may provide a more accurate prediction of avian biophony than individual acoustic indices. Full article

The global crisis of plastic pollution, particularly involving microplastics (MPs) and nanoplastics (NPs), has profound ecological implications. Birds, serving as bioindicators, are especially susceptible to these pollutants. This systematic review synthesizes the current research on the presence, distribution, and impact of MPs and NPs on avian species, alongside advancements in detection methodologies. MPs and NPs have been identified in over 200 bird species across 46 families, encompassing several ecosystems, from Antarctica to Labrador, including Australia, China, and South Europe. Seabirds such as penguins, gulls, and shearwaters exhibit a high burden of MPs in tissues and feces due to fishing debris, while terrestrial species face contamination from urban and agricultural sources. Depending on their composition, MPs can cause gastrointestinal damage, oxidative stress, and bioaccumulation of toxic chemicals, particularly polyethylene and polypropylene. However, challenges in detection persist due to methodological inconsistencies, though advances in spectroscopy and flow cytometry offer improved accuracy. Addressing this pollution is vital for bird conservation and ecosystem health, requiring international collaboration and standardized research protocols. Full article

Thresholds can be an effective tool in conservation planning, as they can form a defensible target for habitat conservation or restoration. Generalized thresholds must be used with caution, however, as threshold responses may vary with species and spatial scale. The objectives of this study were to identify the scales at which forest-dwelling birds respond to both habitat availability and critical thresholds in forest cover associated with their occurrence, and to assess if life history traits relate to either scale of response or critical threshold. Using point count data from the Ontario Breeding Bird Atlas, I generated concentric buffers ranging from 100 m to 10 km radius around a random subset of point counts and described forest cover and species occurrence within each buffer. I assessed the likelihood of occurrence of each species at each scale of analysis using logistic regression and identified forest cover thresholds below which the occurrence of each species becomes unlikely using fitted regression curves and ROC plots. Species varied in their response to both landscape scale and forest cover, based on relative growth rate, clutch size, and site fidelity. The mean response to forest cover was 30.8%, with landscape scale ranging from 200 m to 9 km. Despite this range, pragmatic approaches to conservation planning are still possible. Full article

Urbanization has drastically transformed natural landscapes, threatening biodiversity by reducing species richness and abundance in cities. In this context, seasonal streams serve as refuge areas for various bird species. To determine the role of seasonal streams in conserving native terrestrial avifauna in Algarrobo, an expanding urban environment, we compared bird diversity in ephemeral streams (n = 18) and residential areas (n = 18). Bird counts were conducted during summer and winter. We utilized a diversity index and Generalized Linear Mixed Models (GLMMs) to assess the richness and abundance of native terrestrial birds, as well as the abundance of six migratory birds. Additionally, species accumulation curves verified whether most present species had been adequately sampled. Our results revealed that seasonal streams harbored a greater richness of native bird species than residential areas. Endemic species were also recorded in these streams. The cumulative number of bird species was higher in the seasonal stream environment compared to residential areas. During winter, a higher abundance of migratory birds (Green-backed Firecrown and Gray-hooded Sierra Finch) was observed in seasonal streams. These findings suggest that seasonal streams play a crucial role in conserving native and migratory birds. Thus, protecting and managing these habitats is essential for maintaining avian biodiversity in urbanized areas. Full article

The retinal structure is generally conserved across vertebrates; however, variations occur due to the relationship between environmental factors and visual perception. Birds have adapted to diverse ecological contexts, evolving specialized visual characteristics. In this study, we examined the retina of Audouin’s Gull (Larus audouinii) using light and transmission electron microscopy. This species is particularly intriguing as it is considered an outlier within the Laridae family: despite being a diurnal bird, it exhibits nocturnal/crepuscular foraging behaviour. Our analysis revealed a retina well adapted for diurnal activity, with features such as a retinal thickness comparable to that of other diurnal birds, a well-developed retinal pigment epithelium, and a high cone-to-rod density ratio. However, we also observed characteristics aligned with nocturnal or crepuscular activity, including a slightly increased rod density in central regions and the presence of two distinct types of horizontal cells in the inner nuclear layer. Additionally, the inner retina showed evidence of complex visual processing. These findings suggest that Audouin’s Gull is an excellent model for visual ecology studies due to its specialized adaptations. Full article

Timing and spatial distribution patterns of migratory birds are crucial for their conservation, particularly in Greece, which serves as a vital migratory corridor between Europe, Asia, and Africa. Traditional monitoring methods face challenges due to resource limitations and the country’s complex geography. This study aimed to determine the migration phenology and spatial distribution of 18 species of raptors and soaring birds in Greece using citizen science data from eBird, analyzed with generalized additive models (GAMs). We processed 15,940 checklists for spring migration and 9131 for autumn migration from 2010 to 2023. GAMs successfully modeled the migration phenology for most species, revealing variable peak migration dates in spring and more synchronized migration in autumn, with most species migrating in early September. A spatial analysis highlighted the importance of coastal areas and islands (particularly the Aegean islands and Crete) as key migratory routes and stopover sites. Validation with standardized counts from the Antikythira Bird Observatory showed some discrepancies, emphasizing the limitations of relying on a single monitoring site and the value of broad-scale citizen science data. Our findings demonstrate the effectiveness of integrating citizen science data with robust analytical techniques to fill knowledge gaps, providing valuable insights for designing monitoring programs and informing conservation strategies. Full article