THE SIZE OF HERON COLONIES IN PORTUGAL IN RELATION TO FORAGING HABITAT

Given the importance of the Portuguese heronries within the Mediterran ean region, it is essential to study their ecology and limiting factor s in order to define a global conservation strategy. Data on size and species composition was gathered from 26 Portuguese heronries during s pring 1993. The results were compared with data on type and availabili ty of feeding habitats within a 5-km radius of the colony center (17 c olonies). The number of Cattle Egret (Bubulcus ibis) nests depends on the area of dry pasture and crops within 5-km, while the number of Lit tle Egrets (Egretta garzetta) depends on the presence of freshwater an d saltwater habitats. Compared with other areas in the Mediterranean. Portuguese heronries are dominated mainly by Cattle Egrets, possibly r elated to a comparative lack of freshwater feeding habitats and abunda nce of dry pasture and crops.