PHOSPHORUS AND NITROGEN IN WETLANDS WITH AND WITHOUT EGRET COLONIES

Colonially nesting birds have been implicated in the destruction of th eir nest site vegetation, the most likely mechanism being through an o verload or imbalance of soil nutrients. The numbers of egrets in coast al New South Wales colonies have increased rapidly in the second half of this century since cattle egrets (Ardeola ibis) were introduced. Th is species now nests colonially with three native species: great (Egre tta alba), intermediate (Egretta intermedia) and little egrets (Egrett a garzetta). Thus there is potential for more rapid degradation of the colony site. We measured the levels of phosphorus in surface sediment s, and phosphorus and nitrogen in water at eight colony site wetlands, and compared each to four other wetlands in the same region where the re were no egret colonies. We conclude that levels of both nutrients w ere elevated in colony wetlands. The implications of this result for d eath of colony site vegetation and the conservation of the three nativ e egret species ate briefly discussed.