Long-term population and colony patterns of four species of Tree-nesting herons in the Camargue, South France

;We present an overview of long-term patterns of population and colony dyna mics of four species of colonially nesting herons, in relation to major env ironmental changes that had occurred in the Camargue, southern France, over the last 30 years. We considered the environmental factors: cold, rain, wa ter levels, salinity and rice surface ar ea, simultaneously within a genera lized linear model (GLM) framework. We found no significant association bet ween water levels, rainfall and the number of nests for any species over th e study period. Our final model indicates an effect of time (year) on the t otal number of nests and colonies of Squacco Heron (Ardeola ralloides), Lit tle Egret (Egretta garzetta), Cattle Egret (Bubulcus ibis) and Black-crowne d Night Herons (Nycticorax nycticorax), as well as on the number of nests p er colony for the last two species. The effect of surface area of rice in t he Camargue was significant on the total number of nests of Cattle Egret an d on the number of colonies of Little Egret and Squacco, Heron. The effect of salinity was significant on the number of nests per colony of Black-crow ned Night Heron and Cattle Egret. Our results contrast with some previous s tudies in that they suggest the importance of local rainfall may not be as important as the influence of other local environmental parameters. Our res ults were consistent with a previously reported effect of prolonged freezin g on the number of Cattle Egrets and Little Egrets, but indicated that this effect is important only during extreme years.