The impacts of agriculture on an obligate grassland bird of North America

Abstract

Grassland birds are in decline worldwide and one hypothesis for this decline is habitat loss and degradation through agricultural intensification. The purpose of this study is to investigate the impacts of agriculture on a declining grassland bird, the Savannah Sparrow (Passerculus sandwichensis). Over two breeding seasons nests were located and monitored, adults and nestlings were measured to assess body condition, and fledglings were radio tracked to quantify survival between agricultural and non-agricultural land-use types. The daily survival rate of nests was negatively influenced by intensive agriculture, but fledgling survival was influenced more by the age of the fledgling and year of the study than habitat. No land-use differences were found in the clutch or brood size, arthropod abundance, nor body condition of adults and nestlings. In the second, but not the first, year of the study, nestling corticosterone levels increased between baseline and 30-minute restraint for offspring from non-agricultural sites whereas nestlings from agricultural sites showed no corticosterone response to acute restraint. Our results provide some evidence that agricultural sites compromise nest survival rates and possibly stress response of nestlings, but further research and long-term monitoring is necessary to fully understand the impacts of agriculture on this species.