Urbanization impacts on the trophic guild composition of bird communities

Abstract

Urbanization transforms the landscape and generates loss of pristine habitats. We investigated the urbanization effect on bird communities in a growing South American city (Santa Fe, Argentina) and hypothesized that if habitat structure and human disturbance change along an urban gradient, the richness and abundance of trophic guilds should also vary accordingly. We placed 50 transects 100 m long × 50 m wide in five districts with different levels of urbanization, determined by habitat structure variables. We recorded the number and abundance of species and the amount of pedestrians and vehicles passing through each transect. We recorded 23% of all bird species known for the Santa Fe province and categorized them within 19 trophic guilds. The percentage of area covered by herbaceous vegetation, water bodies and trees and shrubs had a positive relationship with the richness and abundance of most of trophic guilds (hawking aerial, terrestrial, bark and foliage insectivores; terrestrial and generalized granivores; generalized, aquatic diving and foliage omnivores; hawking aerial, aquatic diving and striding carnivores; nectarivores; and aquatic filters). Pavement surface and human disturbance variables had a negative relationship with the richness, and high buildings and pavement surface had a positive relationship with the abundance of terrestrial omnivores and coursing aerial insectivores. Variation partitioning revealed that habitat structure and human disturbance were better predictors of the richness than the abundance of each trophic guild. Results showed that trophic guilds associated to vegetation strata were seen to increase their richness and abundance towards green areas, even if they presented generalist or specialist habits. Urban planners should conserve or manage the surrounded natural spaces when the growth of the city is directed to these areas and increase the availability of environmental features within the urban matrix.