REPRODUCTIVE SUCCESS OF NEOTROPICAL MIGRANTS IN A FRAGMENTED ILLINOIS FOREST

In June-July 1991-1992, we replicated the mist-netting of Robinson (1988, 1992), who captured birds in forest fragments adjacent to Lake Shelbyville in east-central Illinois in 1985-1986. Of all forest-interior Neotropical migrants that were captured, a much high proportion were hatching year (HY) birds in 1991-1992 (29%) than in 1985-1986 (8%), indicating higher reproductive success. The numbers of Brown-headed Cowbirds (Molothrus ater) and the frequency of their parasitism were significantly lower in 1991-1992 than in 1985-1986. However, despite these improvements, reproductive success for Neotropical migrants was still low, presumably because of high levels of nest predation. A significantly lower percentage of adult birds captured in 1991-1992 were forest-interior Neotropical migrants than in 1985-1986 (35% vs 48%).