Population Viability Analysis and causes of death
Animal populations are not static, but they vary over time because of births, deaths and movements of individuals. In the case of endangered species, the annual monitoring of their populations, as well as the marking of chicks with coded rings, readable from long distances, and the later re-sighting of marked individuals, allows us to obtain information such as the number of individuals in a population, the productivity (number of fledged chicks per breeding pair) or the survival rates. With this information, it is possible to perform Population Viability Analyses (PVA), a set of demographic models that help understanding how the population works, predicting the future evolution of the population and, therefore, guiding on the most adequate conservation actions.
Some of these conservation actions consist of mitigating the causes of mortality. Consequently, the identification of the causes of death is essential for implementing appropriate conservation measures. The information from individuals found the encountering and reporting of dead or injured individuals. However, long-term ringing and monitoring schemes, aiming at re-sighting ringed individuals, and complex multievent capture-recapture analysis, offer the opportunity to obtain an unbiased estimate of the fraction of mortality caused by any given cause.