BROOD PARASITISM IN HERONS

We review intra- and interspecific brood parasitism in herons, and des cribe new cases for Little Egrets (Egretta garzetta), Cattle Egrets (B ubulcus ibis), Squacco (Ardeola ralloides) and Purple Herons (Ardea pu rpurea) breeding in the Ebro Delta, Spain. We report also a case of a Little Egret chick that was successfully reared by Squacco Herons. We experimentally evaluated antiparasitic responses to simulated intra- a nd interspecific parasitism using dummy eggs. Large dummy eggs corresp onded in size with normal Cattle or Little Egret eggs, while small dum my eggs were equivalent to the size of normal Squacco Heron eggs. Both egret species and Squacco Herons, deserted their nests significantly more frequently when a large egg was added to the clutch. Thus, the eg ret species were more responsive to simulated intraspecific parasitism while Squacco Herons were more responsive to simulated interspecific parasitism. Size asymmetries between host and parasite, hatching async hrony brood reduction and nest-guarding all seem to be important to th e evolution of brood parasitism in herons.