- Vickery, Peter D.
The Graduate School, University of Maine
This thesis explores two aspects of the breeding biology of grassland birds in southern Maine. In the first chapter, I found significant relationship between nest predation and striped skunk invertebrate foraging effort. The relationship between nest predation and vegetation physiognomy was analyzed on three spatial scales, but no strong correlation was found at any level. These results suggest that skunk nest predation at this site was incidental rather than targeted towards bird nests.
In the second chapter I developed a new method of measuring reproductive success. This method is comprehensive, time-efficient, and non disruptive of nests. This reproductive index was then used to distinguish birds with known high reproductive success with birds of known low success. Vegetative cover parameters from birds with known high reproductive success were compared to vegetative parameters for low success birds, and were also compared to vegetation from territories developed by conventional "spot-mapping." In high-success territories, 17 vegetation features were significantly different (P,0.01) from no-territory vegetation, whereas for "spot-mapped" territories only 8 cover parameters were different and in low success territories just one. This index was then used to test Van Horne's contention (1983) that density can be a misleading measure of habitat quality. None of the three sparrow species in this study showed a clear correlation between high territory density and high reproductive success, thus supporting Van Horne's thesis.