30. Cowbird Distribution at Different Scales of Fragmentation: Trade-offs between Breeding and Feeding Opportunities

The distribution of Brown-headed Cowbirds should reflect the distribution of their feeding (agricultural or grassy areas) and breeding (host) resources. Because an increase in one resource (e.g., agricultural areas) is often at the expense of the second resource (forest hosts), relationships between cowbird abundance, forest area, and number of hosts may reflect this trade-off. We studied cowbird distribution and abundance in the extensively forested Missouri Ozarks and fragmented central Missouri. Cowbirds were more abundant on fragments than on unfragmented Ozark study areas, even though hosts were more abundant in the Ozarks. In the Ozarks, there was no relationship between cowbird and host abundance, possibly because cowbirds there were limited more by feeding habitat than by hosts. In contrast, cowbird abundance on fragments was positively related to host abundance, possibly because cowbirds there were limited more by hosts than by food.