Characteristics of bird niches in a small Indian city: effect of migratory status, season, and environment variables

Abstract

Small tropical and sub-tropical cities frequently retain considerable and diverse green spaces. Such cities can house diverse bird assemblages but these species face conditions varying both spatially (habitats and human activity spread out unequally) and temporally (influx of migratory birds, seasonally varying weather). How do urban birds cope with such conditions? More specifically, do migratory species vary from resident ones in their requirements, and how do resident species deal with variations in conditions? To address these questions, we used an ordination technique, the Outlying Mean Index (OMI), to estimate niche characteristics (OMI, tolerance, and residual tolerance) of 74 resident and migratory bird species in the tourism-dominated Udaipur city, India, across three seasons during 2019–20 using 16 variables that incorporated human presence, land use and trees. OMIs indicated high residual tolerance suggesting that measured variables were inadequate to fully characterize urban bird niches. Contrary to predictions, birds grouped by feeding guilds had similar niche metrics both within and across seasons. Also contrary to predictions, migratory species had more generalized niches relative to resident species. Bird niches were most influenced by trees, effects due to other natural habitats (open areas, scrublands, wetlands) were weaker, and human-related variables (cattle, built-up area, people, vehicles) had the weakest influence. Seasonal niche characteristics computed for 41 resident species suggested that individual species coped with changing conditions differently. Conservation of bird assemblages in small cities will require preservation of city-wide habitat diversity alongside spatially restricting urbanization.