The Great Bustard Otis tarda in Andalusia, southern Spain: status, distribution and trends
Published: Volume 52(1), June 2005. Pages 67-78.
Aims: Between 2001 and 2004 the first comprehensive census of Great Bustards Otis tarda was carried out in Andalusia, southern Spain. This region holds one of the most endangered populations of the Iberian Peninsula. The aims were to establish the locations of current leks and the numbers of birds breeding at them, determine their age and sex structure and reproductive success, and discuss present and past population trends. These data are essential to plan the conservation of this threatened population.
Results and Conclusions: The total estimated number of birds in the region was 338, distributed in 16 leks plus two breeding sites with only females. The species is today extinct in Almería, Granada, and Málaga. The current distribution is highly fragmented, with two main aggregations of three and five leks in the Guadalquivir valley, respectively close to Osuna, in Sevilla province, and at the border between the provinces Córdoba and Jaén. Another group of three leks is located in the northwest border of the region, separated from the rest by Sierra Morena mountain chain. These birds are perhaps demographically more related to the Bustards of Extremadura than to other leks in Andalusia. The Guadalquivir subpopulation is the remnant of a formerly much larger population, which has declined due to the high hunting pressure before the hunting ban in 1980, and to agriculture intensification during the last decades. Great Bustards survive today in suboptimal habitat, but could go through a slow extinction process in the future if habitat conditions are not improved. Man-induced mortality causes have also probably contributed to the extremely female-biased sex-ratio, with an estimated 3.28 females per male, and several leks with only 1-2 males with 4-17 females. Throughout the study period numbers of males and females increased in Osuna, and adult males decreased in Arahal, Gerena and Bujalance. These decreases are not compensated for by the remarkably low productivity (0.08 young per female in September, range of annual values 0.04-0.12). In conclusion, the small numbers of birds, fragmented distribution, extremely biased sex-ratio, high adult male mortality, and low productivity clearly reflect the poor conservation status and serious extinction risk of the Great Bustard population in Andalusia. Conservation efforts should be urgently directed towards improving habitat conditions, in order to increase current productivity values and decrease mortality through collision with powerlines.