Abstract
Data on habitat requirements of the threatened Eurasian bittern Botaurus stellaris are largely qualitative and limited to countries holding small populations. We assessed the habitat spectrum exploited by male bitterns during the breeding season, based on the analysis of 40 booming sites and 33 non-booming sites in 2,500 ha of heterogeneous reed-beds in the Camargue, France. Environmental variables contributing to booming site selection were, in decreasing order of importance, determined by their contribution to multivariate statistical models: water level in April, proportion of open water, density of dry and green reeds, percentage cover of non-reed species, salinity and turbidity of surface water, and reed height and diameter. Overall, booming sites were characterized by a homogeneous cover of relatively sparse green and dry reeds growing with other plant species in shallow (10-15 cm), clear water. Because these findings are contrary to the traditional perception of bittern habitat in Europe, a reassessment of the species' ecological requirements throughout its distributional range is warranted. In the Camargue the main factors involved in habitat selection (water level and dry reed density) are directly associated with site management, and bitterns respond rapidly to slight environmental changes.