Patterns of Nest Usurpation: When Should Species Converge on Nest Niches?

Abstract

The acceptability of a nest to more than one species and the convergence of species on a nest niche is demonstrated through nest usurpation. I compiled examples of nest usurpation from the literature to examine patterns regarding the species and nest sites that tend to be usurped, those species likely to be usurpers, and the habitats in which usurpation occurs. Cavities and enclosed nests are more likely to be usurped than cup nests. Species that excavate or build these types of nests, like the Picidae and the Furnariidae, are likely to be the hosts of usurpers. Particular groups are prone to usurping nests, including introduced species like the House Sparrow (Passer domesticus) and European Starling (Sturnus vulgaris). Cavity usurpations were more likely to be observed in temperate than tropical/subtropical zones, and about equally likely to be observed in closed and open habitats, while enclosed nest usurpations were observed more frequently in open than closed habitats, and more often in tropical/subtropical than temperate zones. Usurpation of all nest types is more likely to occur in tropical/subtropical zones than expected, based on the number of studies in the literature conducted in these zones. Usurpation of all nest types is less likely to occur in open, and more likely to occur in moderately open habitats than expected, based on the number of studies in the literature conducted in these habitats. Instances of cavity usurpation, recorded primarily in temperate zones, across a variety of habitats, do not contribute to these general patterns. Nest-site convergence through nest usurpation may be more likely to occur in moderately open tropical habitats because of : 1) the availability of enclosed nests, 2) the limited structural heterogeneity of the vegetation, which limits the possibility of nest-niche partitioning, and 3) the high diversity of potential nest competitors and predators. In such environments, interspecific nesting associations may be a more effective generalized nest defense strategy than using a nest site that is difficult to find.