Birds, Volume 6, Issue 2 (June 2025) – 11 articles

We analyse data from a rescue database collected at the Innsbruck Alpenzoo (Tyrol, Austria). The sample covers 33 years (1988–2020), and more than 5250 wild birds from 145 species originating from Innsbruck and the surrounding Inn Valley, one of the most densely populated areas in Europe. Both, the total number of birds as well as the number of bird species yearly admitted have increased since 1988. Orphaned nestlings and victims of glass collisions were the most common reasons for admission and responsible for the increase. Species’ susceptibility to accidental causes increased with regional abundance and degree of urbanisation. More urbanised species are characterised by a high proportion of nestlings and juveniles in the sample. The seasonal patterns of deliveries in these species show a peak in the late breeding season, and young birds are particularly susceptible to glass collisions and cat attacks. The species list also includes regionally rare wetland, upland and forest breeders and foreign migrants. Such species show a high proportion of admissions in autumn and collisions with windows play a greater role for short-distance migrants. Our data also suggest that small birds (<15 g body mass) are more likely to collide with glass panes than larger species. In conclusion, our data suggest that basically all bird groups and species are at least occasionally affected by human structures and activities in urbanised landscapes but support the notion that juveniles and migrants are more prone for accidents due to the lack of experience with anthropogenic structures in new areas. Full article

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