Man-induced habitat changes and sensitive species: a GIS approach to the Eurasian Bittern ( Botaurus stellaris ) distribution in a Mediterranean wetland

Modifications to the Massaciuccoli wetland (Central Italy) caused by various human activities were examined in relation to the distribution of the local Bittern ( Botaurus stellaris ) population. From 1993 to1998 we documented the changing distribution pattern of booming males within the marsh, while at the same time gathering information on human utilisation of the habitat. The evolution of the marsh’s layout overtime has been accurately delineated by developing a Geographical Information System. Local customs of marsh utilisation, in particular the illegal setting of fires and the enlarging of hunting pools, had major impacts on its features. The vegetation beds, dominated by Cladium mariscus , proved to be a patchwork mosaic of different-aged plants (from the last fire or cutting), whose densities therefore increased over time. Booming male distribution was uneven within the marsh and varied from one year to the next. The youngest vegetation beds covered more than 50% of the 50 m-buffer zones defined around booming males. A logistic regression model showed that Bitterns favoured unfragmented young vegetation beds (1–3 years). Consideration of the current state of affairs suggests that the necessary renewal of the vegetation could be best achieved through co-ordinated actions carried out in rotation on predetermined plots, covering at least 20 ha in extent and managed at least every 4 years.