Date of Award

Fall 1996

Document Type


Degree Name

Master of Science (MS)


Biological Sciences



Committee Director

Robert K. Rose

Committee Member

Raymond W. Alden, III

Committee Member

Robert L. Ake

Call Number for Print

Special Collections LD4331.B46 H443


North American Breeding Bird Survey data that were collected from 1971-1992 in Virginia, North Carolina, south Carolina, Georgia, Florida, Alabama and Tennessee were used in this analysis of the impact of Brown-headed Cowbird range expansion on four warbler and four vireo host species.

Maps of mean cowbird abundances were produced using kriging for the periods 1971-1975, 1976-1980, 1981-1985, 1986-1990 and 1991-1992. These maps illustrated a complex invasion of the southeastern United States by Brown-headed Cowbird.

Linear regression analyses of host and cowbird abundances within physiographic strata, showed no species to be in decline or increasing in abundance over the entire area. In addition, no patterns of decline within strata were apparent. When significant declines in hosts abundances over time were apparent from these analyses, the effects of cowbird presence and abundance were investigated using multiple regression analyses within strata. In all cases, negative trends in hosts disappeared or resulted in either a lower or only slightly higher r2 value with the addition of the cowbird variables. Because of this, no negative impacts of Brown-headed Cowbird on host species can be demonstrated using Breeding Bird Survey data.

The results of this study support that of others who suggest that physiographic strata may not be meaningful to bird populations. Because of this, trends produced by grouping data in this way may not represent true changes in bird abundances.


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