Microhabitat structure and avian nest predation risk in an open Argentinean woodland: an experimental study

We studied the effect of the general structure of the nest plant, especially the presence of thorns, and the structural homogeneity of the nest patch, on the vulnerability of nests to predation, using natural and artificial nests. Artificial nests placed in non-thorny plants had a significantly lower predation rate and higher daily survival rate than those in thorny plants. The addition of a ‘thorny microhabitat’ around the immediate proximity of nests placed in non-thorny plants did not have any effect on vulnerability of nests to predation. Conversely, natural nests were located in patches of habitat with a higher density of the species of plant that supported the nest compared to patches selected at random. However, daily survival rate was similar for natural nests placed in patches with a higher or lower density of the species of nest plant in the four bird species analysed. Similarly, survival of artificial nests did not increase with the presence of a higher number of plants similar to the nest plant in the nest patch. Thus, the observed patterns of survival for natural and artificial nests did not seem to support the potential prey-site hypotheses. Birds appeared to be the main nest predators in this ecosystem. Behavioural aspects of the identified predators and habitat structure could explain the lack of effect of thorns and nest patch characteristics on nest survival. © 2002 Éditions scientifiques et médicales Elsevier SAS. All rights reserved.