Tag-team takeover: Usurpation of woodpecker nests by western bluebirds

Abstract

Woodpeckers provide important ecological services by excavating nesting cavities that are used by many forest birds and other animals. Demand for nesting cavities by secondary cavity nesters can lead to intense competition for this limited resource. The Western Bluebird (Sialia mexicana) is known to usurp nests from its own and other species. However, the process by which bluebirds take over Eests from woodpeckers larger than themselves has not been well documented. In rder to understand this process, we analyzed 112 hours of video footage of nests of a Black-backed (Picoides arcticus) and a Hairy Woodpecker (P. vlliosus) located in the Okanogan-Wenatchee National Forest in Washington. Usurpation first involves a short period of physical confrontation followed by a prolonged period of constant bresence around the nest. The male and female bluebirds cooperate by taking turns harassing the woodpecker and guarding the nest. This may be of concern to managers as the Black-backed Woodpecker is considered a species at risk in certain locations.