Urbanization has significantly altered the habitat structure and behavioral patterns of animals. In urban environments with frequent human disturbances, animals may undergo adaptive adjustments in their escape behaviors. This study focuses on Eurasian Tree Sparrows (Passer montanus) from five cities across different latitudes in China, comparing their flight initiation distance (FID) in urban and rural areas to assess the impact of urbanization on their escape behavior and the trend of ecological homogenization. The results confirm the established pattern at the geographic level: a reduction of FID in urban habitats and a decrease in FID with increasing latitude. That is, northern populations of the Eurasian Tree Sparrow in China are bolder than the southern populations. In addition, FID is positively correlated with flock size, with rural flocks exhibiting more pronounced group behavior (observed flocking frequency for urban and rural is 28.74% vs. 40.7%, flock size variance is 26.90 vs. 55.63). Despite the differences between northern and southern latitudes, the variability of FID in urban individuals consistently remains lower than that in rural areas, supporting the trend of reduced variability in escape behavior among birds in urban environments. Driven by urbanization, the escape behavior of Eurasian Tree Sparrows tends toward ecological homogenization, meaning that behavioral differences between urban areas in different cities are diminishing. This trend may obscure the behavioral variability brought about by latitude gradients, indicating that urbanization not only shapes the behavioral adaptations of birds but also potentially weakens their behavioral diversity.

Animal behavioral studies are often combined with research concerning cognitive abilities. Larger brains usually mean more complex neural networks and advanced cognitive functions. By measuring the brain size of different individual animals, we can explore differences in behavioral complexity between populations or species. However, obtaining accurate measurements of brain size is challenging both in field and laboratory environments, especially for rare and endangered species. Therefore, there is an urgent need to develop reliable methods for performing cranial brain mass. This study tests which external structures of the avian head can most accurately predict brain size. We selected five bird species from four orders, categorized external head measures into three types of parameters (direct, calculated and composite measurements), and analyzed these in relation to brain mass. The results showed that while head size can partially explain brain mass, the parameters of head height × head width were the most accurate predictors of brain mass in birds (90.4%). In addition, the positive correlation between endocranial volume and brain mass once again confirmed that avian endocranial volume can, to a certain extent, serve as a valid proxy for brain mass. Our study demonstrates that in the future we can more conveniently perform non-invasive measurements to better understand the relationship between bird brain size and behavior, ecology, and evolution.

Nests are important structures for birds to raise their offspring and for signaling. Many birds incorporate feathers into the nest, since feathers were traditionally thought to serve the function of insulation. Hypotheses in recent years have considered that some birds place feathers in conspicuous locations in the nest for decoration to trigger a fear response in the competitors. In this study, we investigated whether decorative feathers could deter nest usurpation by Crested Mynas (Acridotheres cristatellus) by manipulating nest box contents. The results revealed that Crested Mynas preferred black feathers to white feathers as decorations and occupied nest boxes decorated with black feathers significantly less than those decorated with white feathers, suggesting that black decorative feathers in the nest could be more effective in preventing nest usurpation by Crested Mynas and that white decorative feathers may have other functions. The black feathers in the nest are prominently placed at the edge of the nest to convey the message that "this nest is occupied" or "the owner of this nest has been preyed upon" to visitor Crested Mynas, thus effectively preventing them from usurping the nest at a later stage.