Foraging Flights of Nesting Egrets and Herons at a Hong Kong Egretry, South China

Abstract

-Observations of the foraging flights of nesting Great Egrets (Casmerodius albus), Little Egrets (Egretta garzetta), Black-crowned Night Herons (Nycticorax nycticorax) and Cattle Egrets (Bubulcus ibis) in 1997 and 1998 from the A Chau Egretry in Starling Inlet, Hong Kong, China, showed that shallow coastal waters were the major feeding habitat of Great and Little egrets, whose habitat use greatly overlapped. Black-crowned Night Herons, the dominant breeders in the colony, preferred mangroves and fishponds, while Cattle Egrets made most use of freshwater marsh and abandoned paddy fields. Cattle Egrets showed the highest use of feeding habitats outside the Inlet. In both years, Cattle Egrets made the longest median flights at both high and low tides. Black-crowned Night Herons made the shortest flights at high tide in both years while Great Egrets and Black-crowned Night Herons flew the shortest distance at low tide in 1997 and 1998, respectively. In both years, Great and Little egrets flew farther at high tide, when nearby shallow waters were too deep for feeding. Foraging flight distances varied significantly between years only for Cattle Egrets. More Black-crowned Night Herons and Cattle Egrets were involved in group flights. The feeding habitats in Starling Inlet supported far more breeding ardeids than expected for their area, probably because of their high productivity. The short foraging flight distances of Black-crowned Night Herons may reduce foraging costs and help explain the dominance of this species in the colony. Conservation of all wetland feeding habitats in Starling Inlet will be necessary to maintain the present size and diversity of nesting ardeid populations. Received 26 January 1999, accepted 22 September 1999.