Résumé
Habitat composition around nesting sites is one of the important factors that drive the colonial dynamics of waterbirds. Using a Monte Carlo procedure, we compared the changes that occurred over a period of 25 years (1975-1999) in (1) the distribution and composition of tree-nesting heron colonies and (2) the distribution and amount of rice cultivated in the Camargue region of southern France. During the period of 1967-1999, 25 sites in the Camargue were each occupied for at least one breeding season by colonies of tree-nesting herons. Total number of nests, number of nests per colony, and number of colonies varied among the four species considered. During the same period, the proportion of the study area planted with rice fluctuated widely. Overall, nests of all species tended to be located at sites surrounded by a large area of rice fields. However, examination of the results revealed a difference among species in selection of nest colony sites: Cattle Egret (Bubulcus ibis), Squacco Heron (Ardeola ralloides), and Black-crowned Night-Heron (Nycticorax nycticorax) seemed more inclined to nest on sites surrounded by rice fields; whereas Little Egrets' (Egretta garzetta) nest choice was not consistently related to availability of rice fields. That pattern was especially noticeable at a small scale (i.e. <5-km radius around the colony). Our spatial analysis supports previous findings on the effects of rice farming on the colony dynamics of tree-nesting herons. We conclude that different landscape scales are an important consideration for understanding colony site selection and need to be taken into account in the planning and design of agri-environmental development schemes.