Studying the reproductive skipping behavior in long-lived birds by adding nest inspection to individual-based data

The frequency at which individuals breed is an important parameter in population, as well as in evolutionary, studies. However, when nonbreeding individuals are absent from the study area, the reproductive skipping is usually confounded with a recapture failure and cannot be estimated directly. Yet, there are situations in which external information may help to estimate reproductive skipping. Such a situation is found with nest-tenacious birds: the fact that an individual is not encountered in its previous nest is a good indication that it must be skipping reproduction. We illustrate here a general probabilistic framework in which we merged the classical individual capture-recapture information with nest-based information to obtain the simultaneous estimate of recapture, survival, reproductive skipping, and within-colony breeding dispersal probabilities using multi-event models. We applied this approach to Cory's Shearwater (Calonectris diomedea), a long-lived burrow-nesting seabird. By comparing results with those obtained from the analysis of the capture-recapture information alone, we showed that the model separates successfully the probabilities of recapture from those of temporal emigration. We found that the probabilities of future reproduction and breeding-site fidelity were lower for individuals temporarily absent from the colony, suggesting a lower intrinsic quality of intermittent breeders. The new probabilistic framework presented here allowed us to refine the estimates of demographic parameters by simply adding nest-based data, a type of information usually collected in the field but never included in the analysis of individual-based data. Our approach also provides a new and flexible way to test hypotheses on temporal emigration and breeding dispersal in longitudinal data.