Estimating sex specific apparent survival and dispersal of Little Ringed Plovers (Charadrius dubius)

Abstract

Sex differences in survival have consequences to population dynamics making information on sex specific survival important. In birds, females often have lower survival than males, and one of the main mechanisms is considered to be differential reproductive investment. We studied apparent adult survival and local recruitment of a small monoga-mous shorebird, the Little Ringed Plover (Charadrius dubius), with 18 years of capture– recapture data collected from a population breeding in Southern Finland. We expected no sex differences in adult survival because parental care is shared and double-broods and excessive relaying are rare in this northern population. Because apparent survival is the product of true survival and site fidelity, we also estimated breeding and natal dispersal distances within the study area to examine bias in survival estimates caused by permanent emigration. We found higher apparent adult survival in males (0.660) than in females (0.609), but no sex differences in local recruitment (0.080). Breeding dispersal distances were longer in females than in males mainly due to lower breeding site fidelity of females (0.620) than that of males (0.808). Thus, the lower apparent survival of females likely resulted from permanent emigration. Interestingly, the philopatric portion of the population (from local recruitment analysis) had higher apparent adult survival than what was found from the analysis of all adults. These apparent survival estimates that are less likely to be biased by permanent emigration showed no sex differences (males 0.734; females 0.721), supporting our conclusion of no sex difference in true adult survival.