SURVIVAL AND MOVEMENT OF POSTFLEDGING JUVENILE HARLEQUIN DUCKS

Abstract

Age specific survival and movement are important components of demography and population structure, and quantification of these rates is useful for management and conservation. However, information on the postfledging ecology of waterfowl species frequently is unavailable to managers. I studied postfledging survival and movements of juvenile Harlequin Ducks (Histrionicus histrionicus) in the Strait of Georgia, British Columbia, using radio marking and capture-mark-recapture analysis of banded birds captured at coastal wintering areas. Survival of juvenile females was high, providing evidence that female winter survival may be similar among age groups. Radio-marked juvenile males were more likely to die than juvenile females, and juvenile males had lowest local survival rates of all sex-age classes. Proportions of banded juveniles found at their capture location during their second winter did not differ significantly between males and females, suggesting equal dispersal rates, and at least 25% (n 5 9) of radio-marked females moved .30 km from their capture location. These results were unexpected, based on previous evidence for female philopatry and theories of male- biased dispersal in waterfowl, and suggest that males and females both likely contribute to gene flow and demographic connection among populations. Received 14 March 2003, accepted 15 November 2003. The immature stage has been shown to play an important role in population dynamics in some waterfowl species (Coulson 1984, Cooch and Cooke 1991). However, informa- tion on postfledging survival and movement patterns frequently are unavailable to manag- ers. Although age ratios may provide a mea- sure of production for hunted species (Bell- rose 1980) and for species with visually iden- tifiable first-year plumage (Smith et al. 2001, Iverson et al. 2003, Rodway et al. 2003a), age specific survival rates are needed to estimate recruitment into the breeding population (Cooch and Cooke 1991, Perrins 1991, An- derson et al. 2001). Survival rates of juveniles generally are difficult to estimate. Juveniles can be difficult to identify or capture, fre- quently resulting in small sample sizes. Also, survival rates often are confounded by juve- nile dispersal from study areas, and dispersal can be difficult to assess without simultaneous sampling of neighboring populations (Clobert and Lebreton 1991). Thus, information on dis- persal is needed to separate mortality from emigration (Lebreton et al. 1992), which is an important distinction for large scale manage- ment of populations. In addition, although much emphasis has been placed on philopatry of waterfowl to breeding areas (Anderson et al. 1992), little attention has been paid to win-