The western European populations of Northern Wheatear Oenanthe oenanthe have halved over the past two decades. In this context of increasingly fragmented populations, a key issue is to understand the role of immigration in the maintenance of remnant populations. We characterized the local survival, fecundity, recruitment and immigration rates of a small, geographically isolated, coastal French population during a period of population stability, while the regional population was rapidly decreasing (1991–1999). Annual local adult and juvenile survival rates were estimated with capture-resighting data at, respectively, 0.463 ± 0.052 (n = 157 adults) and 0.215 ± 0.054 (n = 363 nestlings). Only 2.1 immigrants joined the population per year (7.3% of all recruits). This annual immigration rate (0.039) is lower than all 14 available estimates for small to medium-sized birds. The local population growth rate depended equally on all demographic parameters, apart from a minor influence of the immigration rate. Within-site breeding dispersal distances were low, and differed between sexes (78 ± 49 m for males, 259 ± 274 m for females). Juvenile and adult survival rates appeared lower than for populations of wheatears settled in high quality habitats, but this deficiency was compensated by high fecundity and the 2 annual immigrants. The small population size (22–27 pairs), extremely low immigration, and strong dependence on local recruits suggest that this population was demographically isolated on a patch of moderate habitat quality, with no chance of rescue by immigration in case of stochastic event. Indeed, this population went extinct in the 2000′s, after a disturbance of unknown origin.
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Vol. 50 • No. 2