author(s)
Saba Khursheed Khan, Kamalpreet Kaur and Aijaz Ahmad Dar

abstract
Urbanization contributes to the loss of the world's biodiversity and the homogenization of its biota. Urban avian communities have reduced species richness, while the density of a few successful species is often higher in cities than in adjacent more natural habitats. They provide highly modified habitat for species that can adapt their feeding and other behaviours, or avoid the new conditions. Urban areas and human populations are rapidly growing. In addition, the urban sprawl has led to a highly fragmented landscape, with islets of suitable bird habitat surrounded by highways and buildings that frequently act as barriers, to birds. These altered conditions have changed the avifauna intensely, with many species disappearing once an area is urbanized, thus resulting in a significant loss of local biodiversity. In a slight majority of studies, bird density increased, but richness and evenness decreased in response to urbanization. But it is less understood which mechanisms generate and uphold these community-level changes. In this review we discuss the most important components of the urban environment influencing birds’ community structure and compile several recent studies to illustrate their effects.