KELSEY, R; HAHN, T.P.; Univ. of California, Davis: Distribution and abundance of a nomadic seed specialist, the red crossbill, in the western United States

Many boreal seed-eating birds wander widely and erratically in search of food. Such species may help reveal how processes occurring over diverse spatial scales, from local habitat selection to continent-wide movement patterns, contribute to distribution and abundance of organisms. Red crossbills (Loxia curvirostra) are particularly interesting; they are highly nomadic and irruptive, with at least 8 distinct vocal (flight call) �types� that differ in size, morphology, and foraging performance on cones of different conifer species. These types remain distinct despite nomadism and occasional sympatry during breeding, but data are scant on their biogeography and habitat preferences. In this study, we examined the relationships among biogeography, vocal type, morphology, and habitat distribution in red crossbills. We used 14 years of field data based on observations and captures of crossbills at 68 sites in 6 regions in Washington, Oregon, Wyoming and California. Call types were distributed non-randomly, with several regions differing significantly in frequency of occurrence and relative abundance of the call types. Geographical variation in bill morphology of captured birds corroborates this result. This variation was largely consistent with expectations based on foraging performance on �key conifers.� These distinct biogeographical patterns are important, given that almost every vocal type has been observed at least occasionally in every region, and provide evidence of large-scale habitat selection and spatial segregation of the different red crossbill �types�. These data represent the first long-term, large-scale examination of �type� specific red crossbill geographic distribution, and provide the basis from which to begin considering the behavioral and ecological mechanisms governing habitat selection and movements of nomadic species.