Theses and Dissertations - UTB/UTPA
Factors affecting reproductive success in hosts of the bronzed cowbird (Molothrus aeneus) in the lower Rio Grande Valley, Texas
Date of Award
Master of Science (MS)
Dr. Timothy Brush
Dr. Frank W. Judd
Dr. Robert I. Lonard
During 1997–99, brood parasitism by the Bronzed Cowbird ( Molothrus aeneus), nest predation, and nest sites were examined in selected songbird species in southern Texas. I found a significantly lower parasitism rate in the Long-billed Thrasher (Toxostoma longirostre ) and Olive Sparrow (Arremonops rufivirgatus) than did Carter (1984) at the same site in the early 1980's. High rates of cowbird visitation to Altamira Oriole (Icterus gularis) nests suggest that cowbirds frequently attempt to parasitize this species. However, orioles probably puncture-eject cowbird eggs from their nests most of the time. Orioles experienced a significantly lower incubation-stage daily nest predation rate (DNPR) than did thrashers and sparrows, and a significantly lower nestling-stage DNPR than did sparrows and Red-winged Blackbirds (Agelaius phoeniceus ). These differences may be explained by oriole nest placement (high, on the tips of branches), which probably keeps the incidence of non-avian nest predation extremely low in orioles. Implications of parasitic behavior, nest predation, nest-site availability, rainfall levels, and nesting biology for host reproductive success are discussed.
University of Texas-Pan American
Copyright 2000 Christopher R. Hathcock. All Rights Reserved.