Migratory behaviour of bird species occurring in critical numbers at Besh Barmag bottleneck in Azerbaijan

A narrow coastal plain located between the Greater Caucasus and the Caspian Sea was recently discovered to be a major avian flyway through Transcaucasia. Here at the Besh Barmag bottleneck in Azerbaijan an estimated 1.24–1.51 million migrants passed through in autumn 2011 and a further 0.65–0.82 million in spring 2012, elevating this bottleneck to international importance. Furthermore, 34 bird species were observed in numbers in excess of the 1% threshold of world or flyway population in at least one of the observation seasons. Due to the high concentration of these species, any dangers affecting this passage can be threatening at a population scale. This study therefore aims to describe the migratory behaviour of these 34 species and subsequently to identify the dangers involved in passage through the area. Collision with anthropogenic obstacles was regarded as the main threat in the coastal plain. Ten (40%) of the species studied and observed in autumn 2011 were flying at the lowest altitudes and are therefore under threat on migration through the bottleneck due to overhead power lines, buildings, traffic and hunting. Planned infrastructural developments with heights of up to 200 m (e.g. towers, wind farms) pose a future threat for an additional 13 (52%) of the study species observed in autumn, making a total of 23 species that would be threatened. Only two species, Pygmy Cormorant Microcarbo pygmaeus and Grey Heron Ardea cinerea, can be expected to maintain their currently safe passage in future as they migrate mainly above 200 m above ground level. In spring 2012, all 14 (100%) of the species that used the coastal plain as flyway, migrated below 50 m and are therefore imminently threatened by collision. Although birds migrating over the Caspian Sea were concentrated at the lower altitudes, there was no identifiable threat for migrants using this flyway, but hazards can be expected in the oil production areas further south.