Brown-headed Cowbirds (Molothrus ater), and to a lesser extent Shiny Cowbirds (M. bonariensis), have expanded their breeding ranges to include that of the Florida Scrub-Jay (Aphelocoma coerulescens). We added the eggs of seven bird species to Florida Scrub-Jay nests to determine if scrub-jays eject foreign eggs. Most eggs were ejected within 1 d of addition, probably by grasp-ejection. Ejection of foreign eggs by Florida Scrub-Jays suggests that cowbirds, should they begin to parasitize scrub-jays, would waste their reproductive effort. Fossil evidence suggests that Florida Scrub-Jays may be former cowbird hosts that have sustained the ability to eject.
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Vol. 75 • No. 1