Summary1. The dynamics of many populations is strongly affected by immigrants. However, estimating and modelling immigration is a real challenge. In the past, several methods have been developed to estimate immigration rate but they either require strong assumptions or combine in a piecewise manner the results from separate analyses. In most methods the effects of covariates cannot be modelled formally. 2. We developed a Bayesian integrated population model which combines capture-recapture data, population counts and information on reproductive success into a single model that estimates and models immigration rate, while directly assessing the impact of environmental covariates. 3. We assessed parameter identifiability by comparing posterior distributions of immigration rates under varying priors, and illustrated the application of the model with long term demographic data of a little owl Athene noctua population from Southern Germany. We further assessed the impact of environmental covariates on immigration. 4. The resulting posterior distributions were insensitive to different prior distributions and dominated by the observed data, indicating that the immigration rate was identifiable. Average yearly immigration into the little owl population was 0AE293 (95% credible interval 0AE183-0AE418), which means that ca 0AE3 female per resident female entered the population every year. Immigration rate tended to increase with increasing abundance of voles, the main prey of little owls. 5. Synthesis and applications. The means to estimate and model immigration is an important step towards a better understanding of the dynamics of geographically open populations. The demographic estimates obtained from the developed integrated population model facilitate population diagnoses and can be used to assess population viability. The structural flexibility of the model should constitute a useful tool for wildlife managers and conservation ecologists.

2006. Local population dynamics and the impact of scale and isolation: a study on different little owl populations. Á Oikos 115: 389 Á400.The understanding of how variation of demographic rates translates into variation of population growth is a central aim in population ecology. Besides stochastic and deterministic factors, the spatial extent and the isolation of a local population may have an impact on the contribution of the different demographic components. Using longterm demographic data we performed retrospective population analyses of four little owl (Athene noctua ) populations with differential spatial extent and degree of isolation to assess the contribution of demographic rates to the variation of the growth rate (l) of each local population and to the difference of l among populations. In all populations variation of fecundity contributed least to variation of l, and variation of adult survival contributed most to variation of l in three of four populations. Between population comparisons revealed that differences mainly stem from differences of immigration and juvenile local survival. The relative importance of immigration to l tended to decrease with increasing spatial extent and isolation of the local populations. None of the four local populations was self-sustainable. Because the local populations export and import individuals, they can be considered as open recruitment systems in which part of the recruited breeding birds are not produced locally. The spatial extent and the degree of isolation of a local population have an impact on local population dynamics; hence these factors need to be considered in studies about local population dynamics and for deriving conservation measures.M. Schaub (michael.schaub@vogelwarte.ch), Swiss Ornithological Inst.,

The demographic reasons of local population extinctions are rarely known which hampers learning for preventing extinction of other populations. Here we study the demography of a population of the endangered woodchat shrike Lanius senator at the edge of its distribution range from 1966 to 1992. We recorded the number of breeding pairs and collected reproduction and capture‐recapture data which were analysed with an integrated population model. Population size and most demographic rates fluctuated, but did not show long‐term trends. The most important demographic driver for the variation in the annual population growth rate was immigration. Despite its dependence on immigration, the local population was not necessarily a sink but may have been part of a balanced dispersal system. A population viability analysis showed that the risk was zero for the population to go extinct due to stochastic events during the 10 years after 1992. Yet, the population went extinct 6 years after the end of the study. The only demographic mechanism that can explain the fast extinction is a stop of immigration. The population was always dependent on immigration due to the strong dispersal of the shrikes and became more isolated due to the overall decline of the species. Our results suggest that the reservoir of potential immigrants may have become insufficient to maintain the local population and highlights that local populations can go extinct without the need of local changes in demography. Successful conservation of bird populations with similar demography as woodchat shrikes need to focus on spatial scales that extend significantly beyond the local one.

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