Habitat preferences of Eurasian Bitterns Botaurus stellaris booming in ricefields: implications for management

The Eurasian Bittern Botaurus stellaris suffered declines in western Europe during the 20th century, partly because of wetland reclamation. The species has been traditionally considered a reedbed specialist but recent studies identified a greater ecological plasticity than previously believed. We investigated habitat associations of a Eurasian Bittern popu- lation that has started to breed in the ricefields of NW Italy since the early 1990s. Boom- ing Bitterns had a higher probability of occurring in ricefields with taller rice plants, more vegetated field banks, more weeds, a larger surface and closer to remaining natural wetlands. The positive effect of field bank vegetation height on the probability that a ricefield hosted a booming Bittern declined late in the season, in contrast to the effects of weeds and ricefield area, which were stronger later in the season. A decreasing impor- tance of vegetation on field banks to booming Bitterns may be a consequence of seasonal changes in habitat structure through the Bittern’s breeding period. The degree of flood- ing did not affect the probability of occurrence of booming Bitterns, probably because most ricefields were homogeneously flooded during the peak breeding season (June– July). Our findings have important implications for the management of Bittern popula- tions breeding in the ricefields of NW Italy. We propose simple conservation actions that may favour the occurrence of booming Bitterns and help the species spread in this novel habitat.