EFFECTS OF PATCH SIZE ON BIRDS IN OLD-GROWTH MONTANE FORESTS

Following habitat alteration or fragmentation, competition, parasitism , and predation from species that live in the new habitats may reduce the survival and reproductive success of species living in the origina l habitats. Negative influences from species that live outside tbe rem nant patches are expected to be greater in small rather than in large remnant patches because more ''external'' species are expected to move through the centers of small remnant patches. We surveyed birds withi n remnant patches of old-growth montane forests on Vancouver Island Ca nada, (1) to evaluate whether the richness and abundance of non-old-gr owth bird species were larger at the center of small rather than large patches and (2) to evaluate whether the opposite was true of old-grow th bird species. More non-old-growth bird species were present at the center of small remnant patches of old-growth than in large old-growth patches. We found no relationship, however, between patch size and ri chness or abundance of old-growth bird species at the center of remnan t patches of old growth. This was true for old-growth species with ope n, cup-shaped nests and cavity nests. Old-growth birds may have been a ffected less in our study area than in other areas because they evolve d within heterogeneous montane forests and interacted with non-old-gro wth species throughout their evolutionary histories or because the con trast between old-growth forests and logged areas was less than that b etween the forests and agricultural/urban areas that were surveyed in other studies.