Relationships between hydrological control of River Red Gum wetlands and waterbird breeding

Fourteen wetlands on the floodplain of the Murrumbidgee River (Murray-Darling Basin, Australia) were surveyed for breeding waterbirds during three annual flood periods. Degree of water control in the wetlands ranged from none to slight to medium to heavy. The wetlands comprised open areas with River Red Gums Eucalyptus camaldulensis. Most, but not all, of the red gums were alive. Precocial waterbirds (those that do not feed their young; mostly Anatidae in this study) did not breed at wetlands with highly controlled water regimens. In altricial waterbirds (those that feed their young at the nest; Pelecaniformes and Ciconiiformes in this study) breeding was not directly related to water level control, but depended on areas of River Red Gums that flooded for at least four months. Within the altricial group, Darter Anhinga melanogaster, Great Cormorant Phalacrocorax carbo and Pacific Heron Ardea pacifica preferred sites with large areas of River Red Gum that flooded for at least four months and large areas of dead River Red Gum (which stayed flooded permanently). Little Black Cormorant Phalacrocorax sulcirostris, Little Pied Cormorant P. melanoleucos, White-faced Heron Ardea novaehollandiae and Yellow-billed Spoonbill Platalea flavipes favoured wetlands with large areas of live River Red Gum that flooded for at least four months. River Red Gum wetlands in which water levels are controlled can be managed for nesting Pelecaniformes and Ciconiiformes. Treeless parts of wetlands can be permanently flooded, but nest trees should not be killed by permanent inundation.