Breeding Flow Thresholds of Colonial Breeding Waterbirds in the Murray-Darling Basin, Australia

Abstract

Biodiversity on floodplains is under increasing pressure as demand for water for human needs expands. Understanding how waterbirds respond to river flows feeding floodplain wetlands is critical for successful management. We analysed data on breeding by colonial breeding large waders-Eastern Great Egret Ardea modesta, Intermediate Egret Ardea intermedia, Little Egret Egretta garzetta, Nankeen Night Heron Nycticorax caledonicus, Australian White Ibis Threskiornis molucca, Glossy Ibis Plegadis falcinellus, Straw-necked Ibis Threskiornis spinicollis, and Royal Spoonbill Platalea regia-in response to river flow for three wetlands in the Murray- Darling Basin, Australia. Each wetland, which included Barmah-Millewa, the Macquarie Marshes, and Lake Merreti, has a distinctive geomorphology and hydrology. There were clear consistent thresholds of flow producing a >0.7 probability of attempted breeding by most species when a daily flow threshold was exceeded for 30-50 days. Flow characteristics were highly correlated and thresholds could also be expressed in terms of the total flow volume July-December and peak flow in September or October. Below thresholds, there was zero probability of breeding for most species. These minimum thresholds provide critical information for management of these wetlands. Our approach provides an analytical framework for estimating thresholds for other floodplains.