Nest-site partitioning in a strandveld shrubland bird community

Nest-site selection may vary adaptively among co-existing species as a result of competitive interactions among the species or in response to density-dependent nest predation. We examined nest-site characteristics and degree of partitioning among 14 co-existing bird species breeding in dwarf strandveld shrubland at Koeberg Nature Reserve, South Africa. Habitat characteristics of nest sites differed significantly among species, indicating strong nest-site partitioning. The principal variables distinguishing nest-site characteristics among species (substrate height, cover at 1 m, cover at 2m) were features that distinguish tall-shrub species which are strongly associated with patches of Dune Thicket from shorter-shrub species which are strongly associated with more open Sand Plain Fynbos. Two groups of species which differ primarily in their selection of habitat patch type within the patchy nesting landscape were identified. One group nested predominantly in low shrubs associated with open Sand Plain Fynbos. A second group nested at a variety of heights within tall-shrub species associated with Dune Thicket. Species within each of these groups differed from each other in their relative nest height (ratio of nest height to substrate height), distance of nest from foliage edge, nest concealment and choice of particular substrate plant species. On average, stepwise discriminant function analysis classified 52.6% of the nest sites correctly as belonging to one of the 14 species, considerably better than the expected random classification of 11.8%. Individual species' classifications were 2-12 times better than a random classification. We suggest that high levels of nest predation may have selected for strong nest-site partitioning in this community.