Estimating temporary migration using the robust design

One of the basic assumptions central to the analysis of capture-recapture experiments is that all marked animals remain in the population under study for the duration of the sampling, or if they migrate out of the population they do so permanently. Burnham (1993, in Marked Individuals in the Study of Bird Populations, 199-213), Kendall and Nichols (1995, Applied Statistics 22, 751-762), and Kendall, Nichols, and Hines (in press) showed that completely random temporary emigration influences only estimates of the probability of capture, these now estimating the product of the temporary emigration rate and the conditional probability of capture given the animal. remains in the population. Estimates of abundance or survival that refer to the entire population, including the temporary emigrants, remain unaffected. Kendall et al. (in press) further showed that Pollock's (1982, Journal of Wildlife Management 46, 757-760) robust design could be used to estimate the temporary emigration rate when the population was assumed closed during the secondary samples. We generalize this result to allow animals to enter and leave the population during the secondary samples. We apply the results to a study of Grey Seals and perform simulation experiments to assess the robustness of our estimator to errors in field identification of brands and other violations of our assumptions.