Agricultural intensification caused steep population decline of the Great Bustard in Iran

The current distribution and recent population trends of the Great Bustard ( Otis tarda ) in Iran were investigated based on a literature review and unpublished data (1995–2008) followed by three years of census (2009–2011) in areas where the species is still breeding. Results suggest that Great Bustards have disappeared from a large part of their former distribution in the country, including East Azarbayjan, Hamedan and Kurdistan provinces. The surviving groups are concentrated in West Azarbayjan where numbers are rapidly declining. The present population is estimated at about 43–48 birds in 2011, confirming a marked decline compared to the 200–300 birds estimated in the early 1990s. About 80–90% of the extant birds are concentrated in the plains of Boukan. The apparent reason for the population decline is agricultural intensification in recent decades. Many areas formerly farmed in a traditional way, and thus suitable for the species, are now under intensive cultivation and often irrigated. The only region where conditions remain suitable for the species in Iran is West Azarbayjan. Great Bustards are found there in Sootav, Yengija-Albolaq and Se Kanian, all around Boukan city. The main crops include wheat, barley, chickpeas, sunflower and alfalfa, and the area has been subjected to a lower degree of agricultural intensification.

This species is omnivorous, taking different foods in differing seasons. In northwestern Spain in August, 48.4% of the diet of adult birds was comprised by green plant material, 40.9% was invertebrates and 10.6% was seeds. In the same population during winter, seeds and green plant material comprised almost the entirety of the diet. Alfalfa is seemingly preferred in the diet of birds from Spain. Other favoured plant life in the diet can including legumes, crucifers, common dandelion and grapes and the dry seeds of wheat and barley. Among animal prey, insects are generally eaten and are the main food for young bustards in their first summer, though they then switch to the seasonal herbivorous preferences of adults by winter. Coleoptera (including beetles), Hymenoptera (including bees, wasps and ants) and Orthoptera (including crickets, grasshoppers and locusts) are mainly taken, largely based on availability and abundance. Small vertebrates, including small rodents, frogs, lizards and chicks of other birds, may supplement the diet when the opportunity arises.
population decline of the Great Bustard Otis tarda in Iran. Bird Conservation International,
Available on CJO 2015 doi:10.1017/S0959270914000409