Demography of Slate-throated Redstarts (Myioborus miniatus): a non-migratory Neotropical warbler

Abstract

Most wood-warblers (Parulidae) are non-migratory residents of the Neotropics and subtropics, and the demographic characteristics of these species are poorly known. I examined the annual survival, reproductive output, dispersal, age of first breeding, and other demographic characteristics of a permanently territorial non-migratory tropical warbler, the Slate-throated Redstart (Myioborus miniatus), based on a 5-yr study of a color-banded population in Monteverde, Costa Rica. Territorial males showed strong site fidelity, but 26% of females engaged in short-distance between-year breeding dispersal. Estimated annual survival of territory holders, corrected for undetected female breeding dispersal, was 0.56 for males and 0.43 for females, values lower than expected and comparable to survival estimates for North American migrant warblers. The lower annual survival of females had two demographic consequences; unpaired territorial males were present in 3 of 5 yr, and some 1-yr-old males appeared to be floaters. Unpaired females or female floaters, however, were not observed. Mean natal dispersal distance was significantly greater for females (935 m) than males (485 m). Estimated first-year survival was 0.29, but this is almost certainly an underestimate because of undetected long-distance, female-biased natal dispersal. Annual fecundity (fledglings per female) was 1.8, less than that of temperate warblers and attributable to small mean clutch sizes and a low incidence of double brooding. Estimated population growth rate (λ) was <1 for both males and females, suggesting that the study population was a demographic sink, most likely due to lower-than-expected adult survival.