Diet of Montagu's Harriers Circus pygargus Wintering in India: Analysing Seasonal, Regional and Sex Differences Using Web-Sourced Photographs and Pellet Contents

Abstract

Studies on the diet composition of bird species provide valuable insights on their habitat use, trophic interactions and prey selection. Prey abundance can drive movements of raptors in their wintering grounds. But such links have been difficult to establish due to the lack of dietary information for most raptor species. Estimating the wintering diet of raptors is a challenge that requires extensive fieldwork across a large geographical area which is often not possible. The methods used in breeding sites such as nest observations are not available in the non-breeding regions. Recently, several studies have demonstrated the use of web-sourced photographs as a tool for understanding the diet of raptors and also the need for combining multiple approaches to get a comprehensive overview of diet. In this study, we use a novel approach by using web-sourced photographs and pellets to estimate the variations in the diet of Montagu's Harrier Circus pygargus, a species in decline, across its wintering range in India. A total of 232 photographs and 391 pellets collected across western India, Deccan and south India during autumn, winter and early spring seasons were analysed. About 53% of photographs and 71% of pellets contained orthopterans, forming the major component of the harrier's diet. The proportion of reptiles, eggs and birds in the diet were similar across both methods. Presence of other insects in the diet was better estimated by photographs (23%) than pellets (8%) while rodent presence was higher in pellets (17%) than photographs (4%). Pellet analysis and photographs showed similar variation in diet across seasons while only pellets showed variation in diet across regions. Photographs also showed that there is significant variation in diet between the sexes of the species, with higher presence of insects and reptiles in the diet of males than females. Our results suggest that a combination of photographs and pellet analysis provide better estimates of wintering diet of Montagu's Harriers.