Survival and Movements of Fledgling Western Bluebirds

Abstract

Indirect estimates of rates of survival for juvenile songbirds typically are used in population modeling. However, survival in the initial post-fledging period can vary widely among species and indirect estimates may yield misleading information regarding populations. This is especially important when considering species that are experiencing population declines, like the western bluebird (Sialia mexicana). I calculated estimates of survival of western bluebirds during the post-fledging dependent (1–7 days after fledge) and semi-dependent (8–20 days after fledge) periods using radiotelemetry on 27 fledglings in a restoration-treated forest of ponderosa pine (Pinus ponderosa) in northern Arizona. Daily rates of survival were 0.96 (dependent)–0.99 (semi-dependent) in the post-fledging period and yielded an overall rate of survival of 0.64. Predation was the primary cause of mortality. Fledglings moved ca. 100 m from the nest during the dependent period and averaged 200–300 m from the nest in the semi-dependent period. Movements were highly variable in the semi-dependent period. My results provide the first estimate of survival for fledgling western bluebirds. Because my estimates were relatively high compared to other species of songbirds, and patterns of movement suggested that adequate foraging resources were available, my estimates should be treated as rates of survival for bluebirds in good habitat when considering populations from a variety of habitats.