Efficiency gain from auxiliary data requiring additional nuisance parameters

In a mark-recapture study of an animal population, live-recapture information may; be supplemented by resightings from marked animals obtained throughout the period of the study and the two types of data analyzed simultaneously. The resighting data can only contribute to estimates of survival probability if they are jointly modeled with the live-recapture data and require the inclusion of additional nuisance parameters. We show that, under quite general conditions, estimates of the original parameters are estimated with the same: or improved, precision despite the inclusion of the nuisance parameters. Banding data from female goldeneye ducks (Bucephala clangula) are used as an illustration.