Avian Conservation and Ecology (Dec 2020)
Using continental-scale bird banding data to estimate demographic migratory patterns for Rufous Hummingbird (Selasphorus rufus)
Abstract
The effective conservation of birds requires knowledge of species-specific population dynamics. Yet these dynamics during migration and across age and sex categories are poorly understood for small birds. The goal of this study was to assess large-scale fall migration patterns of Rufous Hummingbirds (Selasphorus rufus). Because the age and sex categories of this species depart from the breeding grounds and arrive from migration on different weeks, we predicted that each might use different migration routes, differ in migration speeds, and vary in their weekly distributions. Rufous Hummingbirds are among a few declining species for which a large amount of banding data is available during migration and across the migration corridor. We assembled a large hummingbird capture dataset (28,948 captures; 459 unique locations; fall migrations from 1998 to 2013) and used the centroid location of each age-sex-year-week group to calculate migration routes, timing, and speed. We used a utilization distribution kernel to measure distributions during migration. Adult females tended to have a southbound migration route parallel and between those of young and adult males. Moreover, a greater number of young birds migrated south through California in comparison to adult females and adult males. Our results suggest that the migration of each age-sex category is separated by approximately two weeks with adult males migrating first, followed by adult females, and then the young of both sexes; yet migration speed was not statistically different among categories. Last, adult males were captured within a smaller geographic distribution, i.e., the area during any given week of migration, compared with adult females and young. We conclude that different age-sex categories of Rufous Hummingbirds use alternative routes and differ in migration phenology and distributions. Our results suggest that the age-sex categories could be affected differentially by habitat loss, phenological changes, and climates during migration. Considering such demographic migratory dynamics could improve conservation outcomes.
