Effects of age- and sex-biased dispersal on the estimation of survival rates of the Sand MartinRiparia ripariapopulation in Hungary

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Abstract
Intensive ringing of the large Sand Martin Riparia riparia¸ population of Eastern Hungary has been carried out at breeding colonies since 1986. Previous survival modelling has shown a close relationship between the adult survival rates and Sahelian weather conditions. The detection of such environmental effects on juvenile survival is more complicated because mortality is confounded with dispersal, which varies with age and sex. Although juveniles cannot be sexed by morphological characters, this study examines models of the survival and recapture rates of birds ringed as juvenile males and females separately by assuming a 1:1 sex ratio among juveniles at ringing. Using this approach it was possible to identify biologically realistic models which described the data, but different models were selected for each sex. To study variation in the survival rates of birds ringed as juveniles, it is thus important to model survival and recapture rates for each sex separately. The methods presented here require further development. It was not possible to produce unambiguous evidence of real differences in the survival rates of oneyear- old and older birds because age- and sex-related differences in dispersal could affect the results.