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A preliminary study of nest-site competition in a group of hole-nesting birds McLaren, William David

Abstract

This study was restricted to birds using tree-holes as nest-sites. Of a total of 20 species in the study area, only 13 were sufficiently abundant to merit consideration. These fell into three natural groups on the basis of hole size, with only one euryoecious species (Iridoprocne bicolor) nesting in all three groups. Only the group based on holes made by the Colaptes woodpeckers (Flickers) can presently be construed as showing evidence of nest-site competition. Physical and ecological characteristics of nest-sites are analyzed in terms of intensification or amelioration of nest-site competition. The competing species, all using holes made by Colaptes cafer, are Sturnus vulgaris, Sialia currucoides, Bucephala albeola, Iridoprocne bicolor and Falco sparverius. The data suggest that although competition is now present in this group, it may have been absent before the advent of Sturnus in the avifauna. Neither selection for different sites nor competitive exclusion seem to have occurred before the appearance of Sturnus, which now occupies roughly 25% of all available nests, but one or both of these may now be going on.

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