Site fidelity of female caribou at multiple spatial scales

Studies of site fidelity have been hampered by arbitrary designations of sp atial scale and the lack of null models for comparison. We generated null e xpectations of fidelity at different scales from the distribution of radio- tracked animals in a population. We applied the models to space use of sate llite-tracked caribou (Rangifer tarandus caribou), the most vagile nonvolan t terrestrial animal, from populations representing sedentary and migratory ecotypes. We compared distances between consecutive-year locations of adul t females to expectations based on the total range and seasonal range of ea ch population. At the scale of the total range, sedentary and migratory car ibou displayed remarkably similar philopatry, despite a 30-fold difference in size of their population ranges, from time of calving (late May) to bree ding (late October). The most intense fidelity occurred during post-calving when, on average, sedentary and migratory females returned to as near as 6 .7 km and 123 km, respectively, of locations occupied the previous year. At the scale of the seasonal range, the ecotypes differed. Sedentary caribou still displayed fidelity from calving to breeding; migratory caribou exhibi ted fidelity only during late autumn. For migratory, but not sedentary cari bou, inter-year distances during winter were negatively correlated with age , implying that older females were more philopatric. We conclude that repro ductive activities delimit the season of fidelity of female caribou of both ecotypes, and that scale-dependent ecotypic differences in fidelity may re flect different factors of population limitation. A spatially-explicit appr oach to site fidelity is essential for synthesizing patterns across studies .