Status and extinction probabilities of great bustard (Otis tarda) leks in Andalucia, southern Spain

Great bustards (Otis tarda) commonly occur in isolated populations consisting of only a few tens of individuals. Knowing where these are, and understanding the factors affecting their persistence, is necessary to save this declining species. A census (Spring 1999) was therefore made of possible great bustard lek sites in Andalucia, southern Spain. Forty-six males and 79 females were observed and a total of 180 conservatively estimated for the areas we visited. These were distributed among five, possibly six, leks, but most (66-72%) were recorded at only two localities. Through interviews with local people we established that at least two, possibly three, leks had become extinct within the last two decades, and also learned of another lek of 50-70 birds in the north of the region. The precarious status of the four largest visited leks was demonstrated through computer simulation (VORTEX). This showed that under status quo conditions their likelihood of extinction within 100 years is 85-99%. Further simulations demonstrated the disastrous consequences of poaching with extinction probabilities of 95% reached in 8-70 years. However when a hypothetical management scheme was modelled the results were encouraging. In these simulations the number of chicks per female per year was increased from 0.14 to 0.18 and annual mortality of females was reduced from 7.5 to 5%. This resulted in extinction probabilities of only 20% within 100 years at the larger leks. Simple, practical conservation actions to enhance annual recruitment and increase female survival are suggested.