Metropolitan garbage dumps: possible winter migratory raptor monitoring stations in peninsular India

Abstract

Winter raptor migration and movement is poorlydocumented for peninsular India, mainly due to the lack of geographical bottlenecks. We describe, for the first time, the use of a garbage dump in a metropolitan city as an alternative visual winter raptor monitoring station. The daily count, adult to juvenile ratios and species composition of three migratory raptor species, Steppe Eagle Aquila nipalensis, Black-eared Kite Milvus migrans lineatus and Tawny Eagle Aquila rapax are presented. Ground temperatures at the garbage dump site and surrounding area, and the wing beat rate of migratory raptors before and after arrival in the early morning were measured. A total of 355 raptors migrating over a period of six observation days with 250 adults and 105 juveniles were recorded. The temperature of the garbage dump was significantly higher than the surrounding area, while the wing flapping rate was significantly lower over the garbage dump area. It is possible that migrating raptors use garbage dump thermals in the early morning to save energy with soaring and gliding flight (versus flapping flight). We propose that such sites may be used as visual winter migration monitoring stations in metropolitan cities in peninsular India.