INTRODUCTION

The research on which this dissertation is based is part of a broader program to study the factors influencing the abundance and breeding success of Neotropical migrant birds in the forests of south-central Indiana, initiated by Donald Whitehead. I have used theoretical and empirical approaches to understand the effects of forest management practices on breeding birds. The objectives of this dissertation are (1) to describe variation in brood parasitism by Brown-headed Cowbirds (Molothrus ater) among landscape contexts in south-central Indiana, (2) to develop a framework of models that can be used to investigate the effects of habitat edges on avian productivity, (3) to evaluate the effects of timber management practices on brood parasitism and nesting success of birds breeding in active harvest tracts in Yellowwood State Forest (YSF), and (4) to investigate the mechanisms of edge effects using avian abundance data from points in and near maintained forest openings in the Hoosier National Forest (HNF). (A glossary of terms and symbols is provided as an appendix. Early occurrences in the text of terms included in the appendix are italicized.)

In the first chapter of this dissertation I describe within-landscape patterns of brood parasitism by Brown-headed Cowbirds (Molothrus ater) in the forests of south-central Indiana. I test the hypothesis that cowbird abundances are higher near various types of edges than at points further from disturbances, using data collected by Carolyn Frazer Whyte. I test the hypothesis that levels of cowbird parasitism are higher near edges, using nest data gathered by my colleagues and I in various forest contexts. We monitored nests of various species from 1990 to 1993 in six landscape contexts: (1) interior forest, (2) forest adjacent to an agricultural corridor, (3) forest near clearcuts in the Hoosier National Forest, (4) forest near maintained "wildlife" openings in HNF, (5) within small timbercuts in Yellowwood State Forest, and (6) within an old field.

In the second chapter I develop a theoretical framework from which to study the effects of edge and vegetative disturbance on abundance and breeding success of forest birds. In this discourse I focus especially on the effects of cowbird parasitism, but I also consider aspects such as nest predation and the direct effects of habitat loss. Even-aged timber harvest directly reduces population-level breeding success for forest birds by eliminating habitat. It may also reduce the quality of remaining habitat through the effects of edge on breeding success. Edge may reduce breeding success by defluencing birds from settling nearby, decreasing mating success of territorial males, increasing the level of cowbird parasitism, and increasing the level of nest predation. I describe methods to test hypotheses regarding the existence of edge effects on cowbird parasitism, using appropriate null models. I develop models describing various potential mechanisms by which edge effects may occur, and discuss how these models may be used to test which mechanisms are operating in a given system.

In the third chapter I describe results from a field study I designed to quantify the effects of logging on abundance and breeding success of forest birds. I measured brood parasitism and breeding success of birds in eight tracts in YSF in 1995 and 1996. Timber was cut in four of those tracts in the fall of 1995.  I use nest monitoring data to test the hypothesis that reproductive success of birds decreases in proximity to edges. I test the following predictions of this hypothesis: (1) reproductive success is lower in forest sites that have recently been logged than in similar tracts that have not been logged, (2) birds breeding in forest tracts in which timber is harvested experience lower reproductive success after harvest than before harvest.