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Fort Hood Center for Cooperative Ecological Research
Brown-headed Cowbird - Radio Telemetry

Related activities: Cowbird Telemetry Avian Monitoring - Golden-cheeked warbler Nest Predation Crown Fire

This project addresses those terms and conditions, as described in the biological opinion, that relate to the management and control of brown-headed cowbirds (Molothrus ater) on Fort Hood. The unique ecology of the brown-headed cowbird has warranted special attention be placed on cowbird control and management. As an obligate brood parasite, the brown-headed cowbird has been cited as a major threat to a number of neotropical songbirds (Mayfield 1977, Brittingham and Temple 1983). The recovery plans for the golden-cheeked warbler (USFWS 1992) and the black-capped vireo (USFWS 1991) list nest parasitism by the brown-headed cowbird under reasons for listing and current threats.

Fascination with brown-headed cowbirds stems from their unique reproductive strategy that does not require them to raise their own young. Breeding (nest searching and egg laying), feeding, and roosting tend to be spatially and temporally segregated. The uncoupling of these activities can be an adaptive reproductive advantage as they may select and optimize the use of very separate and diverse habitats for specific behavioral strategies.

This specialized reproductive strategy is often at the expense of the host species. Initial studies on Fort Hood in 1987 documented frequency of parasitism of black-capped vireo nests by cowbirds at 90.9 percent (Hayden et al. in preparation). Nest success (the total number of young that fledged at least one young) was at 4.7 percent during this same period. Increasingly intensive cowbird control efforts on Fort Hood since 1988 have dramatically and significantly decreased the frequency of parasitism and increased nest success in 1994 to 12.6 percent and 50 percent, respectively (Hayden et al. in preparation). However, cowbird control programs should not be thought to provide long-term recovery for the species (USFWS 1991). Long-term solutions need to ecologically based and consider land management practices that discourage congregation of large numbers of cowbirds. "One particular alternative that should be considered is trying to control/reduce cowbirds with various management strategies, include management of land, habitat, and cattle" (USFWS 1991).

The primary objective of this project is to study the spatial and temporal patterns of behavior exhibited by the brown-headed cowbird and to determine if cowbirds utilize the landscape nonrandomly. A large component of this work will center on determining how cattle grazing influences cowbird behavior and habitat preference. Cowbirds typically feed in short grass habitats and/or with large grazing mammals (Friedman 1929, Mayfield 1965, Dufty 1982, Rothstein et al. 1986). A radio-tracking study by Thompson (in preparation) documented preference for short grass feeding areas occupied by cattle and suggested that distribution of feeding areas was an important limiting factor in controlling cowbirds. Additionally, work by Thompson and Dijak (in preparation) showed most movements between cowbird breeding and feeding areas to be less than 2 km. Work reported by Rothstein (1984) and Smith (1981) indicated distances less than 7 km between breeding and feeding areas. Providing habitat core areas between 2 and 7 km from potential feeding habitats may significantly reduce impacts associated with brood parasitism. However, these relationships may be site specific and highly dependent on local habitat variables.