A demographic model for a population of the endangered lesser kestrel in southern Spain

Abstract

1. The lesser kestrel (Faleo naumanni) has experienced a dramatic decline in the last 20 years in the Western Palearetic. To help in making decisions for the recovery of tire species, a matrix projection model has been developed using demographic data from an intensively monitored population in southern Spain in 1988-93. Survival rates were estimated using the Jolly Seber modelling approach and Program SURGE. 2. The growth rate of the population was λ = 0.959 ± 0.04. The upper 95% confidence limit of λ is 1.0398, and thus our estimate of λ is not significantly different from that of a stable population (i.e. λ = 1). Using the mean value for λ, the probability of extinction for this population, now consisting of ≃ 1000 breeding pairs, is 35% in 100 years and 98% in 200 years. 3. A sensitivity analysis indicates that population growth was most sensitive for changes in adult survival, followed by juvenile survival, productivity of fledglings, proportion of adults that attempt breeding and age at first breeding. 4. Adult and juvenile survival do not seem easily amenable to management, but the small improvement (8.5%) that could be reached enforcing protective laws substantially reduce the probability of extinction of the population. 5. Productivity is less than half its potential maximum due to massive nestling mortality. Increasing food availability around the breeding colonies through habitat management (e.g. leaving uncultivated strips around fields and favouring cereal crops), or introducing the species in areas containing suitable habitat may substantially increase productivity. Combining these measures with the achievable improvement (8.5% increase) in adult and juvenile survival maximizes the long-term survival of lesser kestrel populations.