Rapid advances in the timing of the spring passage migration through Israel of the steppe eagle Aquila nipalensis

ABSTRACT: We examined phenological change in the spring migratory passage of the predatory steppe eagle Aquila nipalensis from 1977 to 2008. Data were collected at Eilat, Israel, a globally important site for migrating raptors. Changes in the observation dates of spring passage migration were examined using correlation and regression analyses to assess changes over time as well as potential relationships with temperature and with the Indian Ocean Dipole, an index of climate in the wintering area. Over the study period, the number of recorded steppe eagles decreased significantly, as did the proportion of juveniles. Despite the population decrease there was a rapid advance in first spring passage date. Although changes in passage dates were related to environmental conditions in wintering and en-route areas, we suggest that one possible additional reason for such a rapid advance is due to increasing competition between individuals for breeding territories due to dwindling habitats. In addition, changes to some aspects of the passage distribution may be a consequence of a changing age structure.