ESTIMATING TEMPORARY MIGRATION USING THE ROBUST DESIGN

One of the basic assumptions central to the analysis of capture-recapt ure experiments is that all marked animals remain in the population un der study for the duration of the sampling, or if they migrate out of the population they do so permanently. Burnham (1993, in Marked Indivi duals in the Study of Bird Populations, 199-213), Kendall and Nichols (1995, Applied Statistics 22, 751-762), and Kendall, Nichols, and Hine s (in press) showed that completely random temporary emigration influe nces only estimates of the probability of capture, these now estimatin g the product of the temporary emigration rate and the conditional pro bability of capture given the animal. remains in the population. Estim ates of abundance or survival that refer to the entire population, inc luding the temporary emigrants, remain unaffected. Kendall et al. (in press) further showed that Pollock's (1982, Journal of Wildlife Manage ment 46, 757-760) robust design could be used to estimate the temporar y emigration rate when the population was assumed closed during the se condary samples. We generalize this result to allow animals to enter a nd leave the population during the secondary samples. We apply the res ults to a study of Grey Seals and perform simulation experiments to as sess the robustness of our estimator to errors in field identification of brands and other violations of our assumptions.