FATE OF GRACKLE (QUISCALUS SPP.) DEFENSES IN THE ABSENCE OF BROOD PARASITISM: IMPLICATIONS FOR LONG-TERM PARASITE-HOST COEVOLUTION

Abstract

Abstract We tested grackles (Quiscalus spp.) to determine whether they retain egg rejection behavior in the absence of the selection pressure of brood parasitism. Neither Bronzed Cowbird (Molothrus aeneus) nor Brown-headed Cowbird (M. ater) parasitism was recorded in 797 Great-tailed Grackle (Q. mexicanus) nests. Cross-fostered Bronzed Cowbird nestlings, but not Brown-headed Cowbird nestlings, fledged from Great-tailed Grackle nests, indicating that Brown-headed Cowbird parasitism does not select for rejection in these grackles. Great-tailed Grackle populations sympatric and allopatric with Bronzed Cowbirds rejected 100% of model cowbird eggs. An allopatric population of Boat-tailed Grackle (Q. major), a sister species of the Great-tailed Grackle, also rejected 100% of model eggs. Egg rejection in the Boat-tailed Grackle has apparently been retained in the absence of parasitism for as long as 800,000 years since it split from the Great-tailed Grackle. The Common Grackle (Q. quiscula), which lays the most ...