The influence of landscape composition on forest bird communities

In this dissertation, I (1) determined the differential effects of two disturbance types (agriculture and silviculture) and magnitude of disturbance (percent disturbance within 1.0 km of sites) on avian community structure, nesting success, and pairing success within forested landscapes and (2) investigated potential mechanisms responsible for associations between avian communities and landscape composition.; Breeding bird communities were surveyed each year from 1997--1999 at 34 sites within contiguous mature forest, representing a range of disturbance magnitudes (4--59%). Each site was in a forested landscape containing predominantly either agricultural or silvicultural disturbances. I also monitored active songbird nests, determined the pairing success of male Ovenbirds ( Seiurus aurocapillus), surveyed Brown-headed Cowbirds (Molothrus ater) and nest predators, and measured stand-level (25 ha) and nest-patch (0.04 ha) microhabitat at a subset of 10 sites.; My results indicated that type of disturbance within a landscape influenced avian community structure more than magnitude of disturbance. Compared to landscapes disturbed by silviculture, sites within landscapes disturbed by agriculture, irrespective of the amount of disturbance, were associated with fewer forest-associated species, long distance migrants, forest-canopy and forest-understory nesting species and greater numbers of edge-associated species. Local variation in microhabitat and microclimate among landscapes did not explain observed differences in avian community structure. Similarly, pairing success of male Ovenbirds was not strongly associated with landscape composition, but rather with local habitat characteristics. Daily nest survival was lower within forested landscapes disturbed by agriculture than by silviculture, which was best explained by more abundant avian and mammalian nest predators in those landscapes. My results suggest that the type of disturbance within forested landscapes significantly influences avian nesting success by intensifying biotic interactions between nest predators and nesting birds. Because both species richness and abundance of forest birds were greater on sites with higher levels of nesting success, differences in nesting success associated with particular disturbance types within forested landscapes may be an important underlying mechanism of landscape-level differences in avian community structure. Thus, this work provides strong evidence that the types of disturbance within forested landscapes can influence avian community structure and, thus, should be considered in conservation and forest-management plans.