LAUSR

Grassland degradation and fragmentation produced by land use have globally impacted biodiversity. In the Neotropics, the Pampas Grasslands have been greatly altered by agriculture and the introduction of exotic trees. To evaluate the effects of changing habitat features on indigenous grassland fauna, we studied a breeding population of a ground-nesting bird, the Spotted Nothura (Nothura maculosa (Temminck, 1815)), in a natural grassland under cattle grazing in central-east Argentina. We estimated daily nest survival rate (DSR) and modeled it as a function of habitat (distance to habitat edges, cattle density, and nest concealment) and temporal factors. Of the 80 nests found, 64 (80%) failed, predation being the principal cause of failure. DSR was 0.874, estimating a cumulative survival of only 6.8% throughout egg laying and incubation. DSR increased with distance to continuous forests and decreased with nest age. Nests located near forest edges could have increased predation risk because they are potentially exposed to forest-dwelling predators in addition to grassland-dependent predators. Considering the low success found and the ongoing invasion of exotic trees in the region, we encourage governments to protect large areas of grassland to ensure adequate nest success for Tinamous and other ground-nesting birds.