Long-term trends in great bustard (Otis tarda) populations in Portugal suggest concentration in single high quality area

摘要: Abstract Areas of occurrence, population trends and extinction patterns for great bustard Otis tarda populations in Portugal are described a 22-year period (1980–2002). The major were large decline the 1984–1995 period, followed by fast post-1995 increase. Most this variation was explained trend observed single site, Castro Verde, where has been increasing, contrast with all other areas have declining. Eight local extinctions documented, probability increased below threshold 30 individuals initial (1980) population. Agricultural intensification, illegal hunting, road power line building, afforestations main causes extinctions. exceptional character Verde is maintenance good habitat quality, existence conservation project an agri-environmental scheme promoting farm management compatible conservation. Stochastic computer simulations, using VORTEX, suggested that migration from sites into likely, as productivity alone could not explain Portuguese estimated at 1150 birds 2002, which 912 concentrated Verde. present increasing concentration bustards site might lead to extinction, particularly due environmental stochasticity.