Breeding territory fidelity in a partial migrant, the American dipper Cinclus mexicanus

Abstract

178.American dipper Cinclus mexicanus populations are frequently composed of residentindividuals that occupy permanent territories year round and migratory individualsthat overwinter with residents but migrate to breeding territories on higher elevationcreeks each spring. Between 1999 and 2004 we examined how migratory strategy(resident/migratory) and sex differences influence breeding territory fidelity ofAmerican dippers occupying the Chilliwack River watershed, British Columbia,Canada. Counter to expectation we found that the migratory strategy of Americandippers did not influence whether birds breeding in one year were found on theirformer breeding territory in the next. Migratory strategy also did not affect theprobability that known surviving dippers occupied the same breeding territory in thefollowing year. Males and females were equally likely to be found on their formerterritory in the following year (females 43%, males 41%) and known survivors hadsimilar levels of breeding territory fidelity (females 74%, males 68%). However,breeding territory fidelity of males and females varied in response to different factors.Surviving female dippers were more likely to be found on their former breedingterritory in the subsequent year following a successful breeding attempt than anunsuccessful breeding attempt. Prior reproductive performance did not influencewhether surviving male dippers were found on their former breeding territory. Maledippers were more likely to be found on their former territory and, if they survived,have higher breeding territory fidelity when their mate also returned to that sameterritory. Mate retention also influenced whether females were found on their formerterritory in the following year but had no effect on the breeding territory fidelity ofknown survivors. We argue that sex-specific dispersal decision rules in Americandippers are driven by sex differences in the predictability of breeding performancebetween years and sex differences in how mate retention influences subsequentreproductive success.H. A. Middleton and D. J. Green (correspondence), Centre for Wildlife Ecology,Department of Biological Sciences, Simon Fraser University, 8888 University Drive,Burnaby, BC V5A 1S6 CANADA. E-mail: djgreen@sfu.ca. C. A. Morrissey, CanadianWildlife Service, 5421 Robertson Road, Delta, BC V4K 3N2 Canada.