[Objectives] With the development of global urbanization, urban areas are constantly expanding, and natural habitats around cities are being squeezed, resulting in a decrease in area and an increase in fragmentation. The process of urbanization will have a significant impact on ecosystem functions, which may lead to birds being forced to adapt to urban habitats and exhibiting homogenization of functional traits. However, there is relatively little research on the impact of urbanization on birds in China, especially on the functional traits through which urbanization will affect birds. Therefore, this study aims to understand the differences in bird species richness and functional diversity under urbanization gradients, and whether it supports the moderate disturbance hypothesis. Also, the study compares the differences in functional traits of birds in urban, suburban, and outskirts to explore which functional traits will affect birds’ adaptation to urban habitats. [Methods] We conducted bird surveys on three different urbanization intensity patches in Hangzhou, including 15 urban patches, 15 suburban patches, and 15 outskirt patches. Each urban survey area with varying levels of urbanization disturbance includes 3 patches of lake water habitats, 5 patches of mountain habitats, and 7 patches of green habitats. We calculate the species richness and functional diversity of birds in different urbanization levels in the region and compare the differences in functional traits of birds in urban, suburban, and outlying patches to explore which functional traits will affect the adaptation of birds to urban habitats. Bird surveys were conducted in November 2022, January to February 2023, March to April 2023, and June 2023. We designed a 1.5 km long survey transect of equal intensity for each patch and recorded the bird species and numbers seen or heard on both sides of the lines. We calculated the species functional richness, functional dispersion, Rao’s Quadratic Entropy, and Community Weighted Mean for each patch to evaluate the diversity of bird communities. We selected 30 functional traits to assess avian functional diversity and calculated functional diversity and community-weighted means (Table 1). The first four axes of the PCoA analysis, which accounted for more than 80% of the variation, were used as the new “traits” to calculate functional diversity. Mann-Whitney U test was employed to analyze the significance of differences in community-weighted means among different regions. [Results] The bird species richness level is highest in outlying patches, but suburban patches have higher bird functional richness (Table 2). Although the species richness and functional diversity in urban areas are lower than those in suburban areas and outlying patches, the overall proportion of species composition in urban areas is also higher, and a higher degree of urban greening supports a certain level of bird species diversity. There are significant differences in nest site selection, clustering, and feeding habits among birds in urban, suburban, and outlying areas (Fig. 3). Compared to birds in suburban and outlying areas, urban birds tend to build nests in tree crowns rather than on the ground or in shrubs (Fig. 5) and are more inclined to form larger groups (Fig. 6). In terms of feeding habits, the proportion of urban birds feeding on flowers and fruits is relatively high, while the proportion of feeding on invertebrates is relatively low (Fig. 4). We did not find significant differences in body morphometrics among birds in urban, suburban, and outlying areas. [Conclusion] The moderate disturbance hypothesis of bird diversity under different urbanization gradients in Hangzhou is reflected through the functional diversity of birds. Suburbs with moderate urbanization disturbance intensity have higher functional diversity, while outlying areas have the highest species richness. Urbanization mainly affects birds through functional traits such as feeding habits, nest sites, foraging layers, and flocking behaviours. Among them, flocking behaviours, nest sites, and feeding habits are the functional trait groups that distinguish urban birds from other birds the most. The low coverage of shrubs in cities, the high risk of human activities from the ground, and the tendency of vegetation types towards landscaping plants may be important factors contributing to significant differences in the feeding habits and nest sites of urban birds. Urban habitats, as a new and unfamiliar environment, are easier for larger groups of birds to adapt to. Improving urban shrub coverage, optimizing the selection of bird-feeding plants in landscaping, increasing and preserving ancient and dead trees, and providing artificial nests are crucial for birds to adapt to urban habitats.