Urban heronry birds tolerate human presence more than its conspecific rural birds

Abstract

Urbanisation is a major threat to biodiversity by forcing animals to either adapt to it, emigrate or face extinction. Wetland depended birds, and in particular heronry birds, are known to be adapted to fresh urban conditions in Kerala, India. They nest on large trees and forage at waste yards and fish markets in urban sites. We used flight initiation distance (FID) as a measure of bird’s tolerance level to humans and to study urban adaptation in heronry birds. When a foraging bird of interest was spotted, we walked towards it holding a rangefinder to measure the FID. We studied this for 237 and 217 foraging birds in urban and rural sites, respectively. We also counted the number of birds in the foraging ground before walking in order to study the effect of group size on FID of the targeted bird. The FID of all bird species, except the intermediate egret, was significantly shorter in urban sites. While the habitat type affected FID, the group size and the interaction between group size and habitat type did not. This study concludes that heronry birds tolerate human presence in urban habitats more than in rural habitats, indicating urban adaptation of heronry birds.

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