Variability in breeding parameters of the Squacco Heron Ardeola ralloides

Abstract

The Squacco Heron Ardeola ralloides is considered to be vulnerable throughout its European breeding range. The largest populations occur in eastern Europe where the most serious declines have been reported (Tucker & Heath 1994). In the western Mediterranean, numbers have fluctuated with some populations showing a slight increase (Heath & Evans 2000, Kushlan & Hafner 2000). However, breeding populations are small and susceptible to catastrophic events (Hafner et al. 2001). In the Mediterranean region the greatest threat is the loss and deterioration of freshwater feeding and breeding habitat (Tucker & Heath 1994, Hafner & Didner 1997). During the past 20 years the breeding biology of colonial herons in Europe has been the subject of many studies and for most species there is a considerable body of data (see Kushlan & Hafner 2000). The Squacco Heron is the least known with few published data on breeding biology (Sterbetz 1960–61,Voisin 1991, González-Martín 1994, Hafner & Didner 1997, Hafner et al. 2001). As long-term data on breeding parameters has revealed a considerable decline in clutch size, and hence, brood size (Hafner et al. 2001) there is concern for the Squacco Heron in the Camargue, a wetland complex which holds 80–90% of the total French population. Here, we tested whether breeding parameters (clutch size, brood size, etc.) varied between colony site at four colonies studied in 2000. We estimated nest survival probabilities during egg and nestling periods, the number of fledglings per breeding attempt and a body condition index for the chicks.