Interspecific feeding is an uncommon behaviour where an individual of one species feeds individuals (mostly offspring) of another species. Observations have been made in many avian species but causes of this behaviour remain unknown and no hypothesis was proposed to fully explain its occurrence. In this review, I collected observations of interspecific feeding in birds reported during the last 40 years and compiled a comprehensive dataset based on all published reports of interspecific feeding. It consists of 186 cases observed in 107 species worldwide and summarizes the information on involved species, their age, sex, and possible causes of this misdirected parental care. Additionally, I report a case of Great Spotted Woodpeckers' Dendrocopos major young fed by Eurasian Nuthatches Sitta europaea. Observations of interspecific feeding are highly skewed in favour of North American and European species, probably due to historical (long research and ornithology traditions) and language issues (publishing in English). Interspecific feeding does not seem to be related to nest type but is mostly associated with males allured by loud calls of nestlings from nearby allospecific nests. However, most of the observations remain only anecdotic and an empirical research that would try to find plausible explanations of the evolutionary advantages of this behaviour still remains to be carried out.

The Eurasian Jay Garrulus glandarius is a highly polytypic bird species composed of 34–36 subspecies. The contribution of formation of glacial refugia to the evolutionary process that generated its tremendous diversity has not been studied. We investigated the contribution of microrefugia to the subspeciation process of the Eurasian Jay in the Japanese archipelago. By assessing genetic diversity and reconstructing a mitochondrial phylogenetic tree, we asked whether divergence of a subspecies on a peripheral island (Sado Island) from the subspecies on the mainland of the Japanese archipelago (Honshu and Kyushu, hereafter mainland) occurred via formation of a microrefugium outside the mainland macrorefugia. We also assessed morphological differences between the Sado Island and mainland jay populations. We tested whether the observed morphological differences can be explained by adaptation of the Sado Island population to a species-poor microrefugium. Genetic analyses inferred that the Sado Island population survived in a refugium outside the mainland macrorefugia from around the late Middle to Late Pleistocene. The morphology of the Sado Island jay population was characterized by greater trait variance, larger body size, and a disproportionately large bill when compared with the mainland population. These results are consistent with the expected patterns of morphological evolution in microrefugia with reduced species diversity. We suggest the importance of ecological release in a microrefugium on Sado Island for the evolution of geographical variation of the Eurasian Jay in the Japanese archipelago. This is the first study to assess the significance of microrefugia for the diversification of the Eurasian Jay.

Urbanization presents wildlife with many novel environmental challenges and opportunities, including navigating new physical structures and exploiting unique food bases. Thus, animal species that persist or thrive in urban environments may have superior cognitive abilities that allow them to navigate and solve anthropogenic problems. Prior studies have shown neural and behavioral differences between animals inhabiting urban and rural environments, but few have tested cognition-related behavioral responses of animals in an urban context. We administered a novel foraging challenge to caged male House Finches Haemorhous mexicanus — a successful urban and native desert species in the southwestern United States — captured from two urban and two rural locations to examine population differences in problem solving. This task involved opening a tin lid that was slid over the bird's normal small food dish and left only slightly ajar (with no food visible). Male House Finches display exaggerated, sexually selected plumage color that is dependent on diet, so we also tested the hypothesis that more colorful males can better solve foraging problems. We found no differences in problem solving success between urban and rural birds. However, among rural birds, we found that redder males were more likely to solve the foraging task than less-red males. Also, birds that lost more mass during the study were more likely to solve the task, but this was only true among less colorful birds. Our results are consistent with the hypothesis that plumage redness reveals foraging skill in House Finches found in their native environment.

Some waterbird species are believed to have an impact on other waterbird species as they are able to usurp a limited habitat and destroy vegetation. In this study, we have analysed the nesting dynamics of five waterbird species: Grey Heron Ardea cinerea, Great Cormorant Phalacrocorax carbo, Little Egret Egretta garzetta, Black-crowned Night Heron Nycticorax nycticorax and Cattle Egret Bubulcus ibis, that had settled in a colony in the Royal Castle Park of Racconigi (Cuneo, NW Italy) over a 17-year period (2000 to 2017). The Great Cormorant and the Cattle Egret settled in the colony in 2008 and 2012, respectively. We analysed the relationships between the number of breeding pairs of the five species. In addition, we used the time series forecasting method to study the nesting dynamics and the impact of the new settlements on the pre-existing colony. The number of nests of the Great Cormorant and the Cattle Egret increased annually, and these species significantly affected the nesting trends of the other pre-existing species: Grey Heron, Black-crowned Night Heron and Little Egret. The Grey Heron mainly suffered from the occupation of its old nests by the Great Cormorant from 2008 to 2013. However, since 2014, the Grey Heron has been able to react, by displacing its breeding site to the tops of trees adjacent to the old heronry, and this has resulted in an even greater number of nests than before 2008. The Black-crowned Night Heron and the Little Egret suffered more from the settlement of the new species than the Grey Heron did, and started to suddenly or gradually abandon the breeding site. The colony has been modified profoundly by the settlement of the Great Cormorant and the Cattle Egret, and it is still subject to dynamics that could transform it in the coming years.

Changes in biometric characteristics of a migrating bird population at a given capture site could reflect that the migration strategies of the species may be changing. A robust data set (15,520 records) was used to analyse the changes in biometric characteristics of the Eurasian Blackcap Sylvia atricapilla in western Hungary between August and October during the study period (2001–2019). All age and sex classes displayed similar phenology of monthly captures and biometric change: the average wing length, fat score and body mass increased in the migrating population from August to October. This could be explained by changes in the morphometric distribution of different migrating populations, in later months more birds might arrive from a larger distance, primarily from the Baltic regions and the Czech Republic. The biometrics of juvenile birds captured in August did not change significantly from 2001 to 2019, while the wing lengths decreased and fat scores increased significantly between 2001 and 2019 in September and October in both sex classes. This could be explained by a change in the migration distance or different morphology of individuals from the north which stopped over at the study area. Due to the global warming and habitat changes in the last decade, the shorter migration route and favourable conditions at overwintering areas north of the Sahara or around the Mediterranean could favour Blackcaps which migrate a shorter distance.

Natal dispersal is the movement from the natal site to the colony of the first reproduction, while breeding dispersal is the movement from one breeding colony to another within or between breeding seasons. These processes are major determinants of genetic structure and a key component of population dynamics. In this study we investigated whether age of recovered bird (immatures, adults) and/or period (three multi-year periods characterized by various climate change dynamics) of recovery from the breeding season affect distance and direction of dispersal from the natal colony in Grey Herons Ardea cinerea nesting in Central Europe, in Poland. We found that the distance of dispersal from the natal area for Grey Herons ranged from 0 to 392 km with mean ± SD 84.1 ± 99.1 km (N = 72). Independently of periods, individuals recovered as immatures had longer dispersal distance than those recovered as adults. Our study revealed that proportion of recoveries representing strong natal fidelity (within the distance of ≤ 38 km around the natal colony, N = 37, 51.4%) differed significantly between the studied periods with the highest proportion (71%) in 1981–2014 and lower proportions in periods 1932–1939 (35%) and 1940–1980 (27%). We also found that the distance of dispersal from the natal colony was affected significantly by the period, with the distance in 1980–2014 being significantly shorter compared to 1940–1980 and with a tendency to be shorter than in 1932–1939. Direction of dispersal from the natal colony was affected significantly neither by period nor age of recovered birds. On average Grey Herons dispersed with a marked SW directional component. Our results indicate that Central European population of Grey Herons have shortened average distance of dispersal from the natal colony since the 1930s. This observation is concordant with changes reported for other European waterbirds.

Despite a huge diversity of egg shapes among birds, similar egg shapes occur in species that differ in habitats and are not phylogenetically closely related; this indicates the presence of factors limiting the egg shape variability. We assume that one of these factors is a general pattern of egg shape change across all birds. We tested a hypothesis of allometric patterns of egg morphometric traits (radii of blunt end (infundibular zone, ri), pointed end (cloacal zone, rc), lateral zone (rl) and maximum diameter (D)) scaling against egg length (L). Phylogenetic allometric analysis was applied. We also studied hierarchical distribution of variation in egg traits at different taxonomic levels in order to determine the degree of egg shape variability on each of them. We revealed allometric patterns in the scaling of egg traits: D and ri scaled against L with negative allometry, while rc and rl were positively allometric. A high degree of covariation was observed between the length and diameter, radii of the lateral and infundibular zones, i.e. traits that are associated with the overall size of an egg, the degree of its elongation, and the shape of infundibular zone. Evolutionary correlation between L and rc was rather low. The greatest variation of egg traits resided at the level of orders. The identified general trends in egg shape variation are realized on the basis of various groups of birds in phylogenetic and ecological sense that assume the influence of these factors on the bird's egg shape.

Agricultural expansion at the expense of natural habitats and the intensification processes in agricultural production are globally among the main causes of biodiversity and ecosystem services loss at large scale. This process can completely alter food provision for birds and have negative consequences for their diet and breeding performance. Under the hypothesis that changes in land use limit food resources for raptors, our aim was to analyze variation in nestling diet between natural areas and areas with different degrees of agricultural intensification (natural forest, traditional farmland, intensive farmland) in a population of American Kestrel Falco sparverius breeding in nest boxes and cavities. Through the analysis of pellets and prey remains collected during the reproductive season of 2012–2013 we found no differences in diet diversity among areas and the diet in the three areas was monopolized by arthropods. However, the diet did change in composition between areas. Numerically, Orthoptera dominated the diet in the three areas, although with a higher percentage in the forest area. The frequency of vertebrate consumption was affected positively by the area occupied by natural forest and stubble, while the soybean cover affected the consumption in a negative way. In both agricultural areas, the diet was complemented with different groups of arthropods suggesting that changes in land use generate a functional response in the American Kestrel that is able to take advantage of available resources in each sampling area. Long-term analysis of diet variation within the framework of agricultural intensification and its relation with demographic parameters and individual performance will allow to evaluate the impact of this variation in the diet on kestrels.

Mixed-species flocks of birds are cohesive groups of two or more different species that are kept in formation by systematic behavioral interactions among the members of the flocks. Typically, mixed-species flocks form themselves around a nuclear species, which presents a specific pattern of movement during foraging, and a song that is recognized by the other species. In the understory of Neotropical forests, representatives of the family Thamnophilidae, in particular species of the genus Thamnomanes, have become adapted for the role of nuclear species in mixed-species flocks. In the present study, we describe the mixed-species flocks led by individuals of Bluish-slate Antshrike Thamnomanes schistogynus in a forest dominated by bamboo Guadua sp. in southwestern Brazilian Amazonia. We collected data within a 600 × 600 m grid subdivided into 36 1-ha plots, with a total area of 36 ha. Within this grid, we delimited the home ranges and core areas of the resident mixed-species flocks. We also identified the composition of each flocks, frequency, fidelity of its members and determined the relationship between mixed-species flocks and vegetation structure within the grid. We delimited the home ranges of eight mixed-species flocks. The mean home range, estimated using the Minimum Convex Polygon method, was 3.45 ± 0.17 ha, and estimated using the autocorrelated kernel density estimation method was 3.65 ± 0.15 ha, and the mean core area, 1.14 ± 0.03 ha. The home ranges of the mixed-species flocks led by T. schistogynus in southwestern Amazonia are among the smallest recorded in species of the genus Thamnomanes. We identified 71 different bird species in the mixed-species flocks with a mean of 41.1 ± 2.1. While the geographic distribution of the lead species T. schistogynus coincides almost exactly with that of the bamboo forests of southwestern Amazonia, our results did not indicate any systematic relationship or fidelity between the mixed-species flocks led by this species and the bamboo forest.

Study of population genetic structure is essential for insight in species biology, but mechanisms of its formation and factors influencing it remain insufficiently understood. Here we analyzed differentiation among populations in small colonial seabird of North Pacific, the Parakeet Auklet Aethia psittacula, which was previously considered as a monomorphic species. We compare our results with data on congeneric species to investigate the most important factors affecting the process of population differentiation in Aethini. We analyzed morphometric measurements, mitochondrial DNA control region fragment and microsatellite loci from six Parakeet Auklet colonies spanning the breeding range. Although results of microsatellite variability analysis did not reveal differences between birds from different colonies, results of control region variability and morphometric analyses testified for a slight but significant differentiation between birds from the Aleutian Islands and other parts of their range. They were significantly smaller in most linear parameters measured and had higher body condition (expressed as the scaled mass index). The results of mtDNA analysis and discrepancy between different types of genetic markers indicated that birds from Aleutian Islands and from the other parts of their breeding range probably originated from different refuges and the differentiation of mitochondrial lineages between them took place around 100 000 years ago. Our results and conclusions from the comparison with congeneric species indicated that foraging and migration patterns seem to determine population structure in small planktivorous alcids, with panmixia in highly mobile species, clear population differentiation in resident species and intermediate population differentiation in more dispersive species.

Leukocyte profiles, such as the heterophile/lymphocyte (H/L) ratio, are influenced by several ecological and ecophysiological factors and are generally considered to be independent and robust indicators of stress levels in birds. We tested the hypotheses that Semipalmated Sandpiper Calidris pusilla presents a positive association between physiological stress (H/L ratio) and molt, and that there should be a negative association between physiological stress (H/L ratio) and body condition (mass). During its annual cycle, Semipalmated Sandpiper performs long-distance migrations and often arrives in South America in September/October when it can undergo molting before its migration to the north. In May, while preparing to return to its reproductive sites, Semipalmated Sandpiper increases its body mass. The research was carried out on Restinga Island of the Rio Paraíba estuary in northeast Brazil. Data collection took place during the wintering of Semipalmated Sandpiper in October 2017 and February and May 2018. We found a positive association between the H/L ratio and the presence of molt in October and February, but a negative association between the H/L ratio and body mass in May. Our results support the hypotheses that the presence of molt should be positively associated with the H/L ratio due to the high energy and nutritional costs that molting requires and that the H/L ratio and body mass should be negatively associated due to the favorable nutritional status of Semipalmated Sandpiper during its preparation to migrate to its reproductive areas.

Collisions with glass or glass-covered objects are an important source of bird mortality worldwide. In this study, we investigate bird-glass collision pattern with the help of novel method using marks left by birds on glass surfaces. We surveyed 85 glass bus shelters every 12 days over a year to evaluate which parts of glass surfaces have the highest risk of collision. Among 178 bird-glass collisions recorded only 3% took place within 10 cm from glass edge, although this glass band (i.e. 0–10 cm from edge) covers over 30% of the whole glass area, on average. More inner parts of glass (10–70 cm from glass edge) had collision frequency slightly higher than expected by their coverage or proportional to their coverage. Different collisions recorded at one glass seemed independent suggesting no spatial aggregations within single glass. This study is the first to demonstrate the non-random risk of bird collision in relation to position on the glass surface and may suggest that there is no need to implement mitigating measures, like visible markers placed on the glass, closer than 10 cm from the glass edge.