Efficiency gain from auxiliary data requiring additional nuisance parameters

In a mark-recapture study of an animal population, live-recapture informati on may; be supplemented by resightings from marked animals obtained through out the period of the study and the two types of data analyzed simultaneous ly. The resighting data can only contribute to estimates of survival probab ility 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 par ameters. Banding data from female goldeneye ducks (Bucephala clangula) are used as an illustration.