Hydrological Variability in Floodplain Wetlands Promotes Bird Diversity and Abundance

Abstract

Floodplain wetlands, despite their significant ecological and cultural value, are among the most degraded ecosystems globally. Recent human impacts on natural river systems have resulted in altered hydrological regimes, typically reducing flooding of floodplain wetlands. Changed flooding regimes may impact the birdlife reliant on floodplain wetlands for habitat and food resources. Using data from 196 bird surveys recorded across several years, we investigated the response of waterbirds and woodland birds to flooding regimes at six billabongs along the Birrarung (Yarra River) in Melbourne, Australia. We modelled how the species richness and abundance of birds responded to presence of water, water level and duration of flooding. We assessed the responses of waterbirds, woodland birds, bird foraging guilds and several bird species culturally significant to local Traditional Owners, the Wurundjeri Woi-wurrung people. Waterbird richness and abundance were higher at flooded billabongs, and at intermediate water levels and durations of flooding. Woodland bird richness and abundance had mixed responses to these hydrological variables and were often more strongly influenced by site factors. Foraging guilds and individual species also exhibited variable responses to water levels. For example, waterfowl and insectivores were more abundant when billabongs were flooded at intermediate to high levels, while granivores were more abundant at low water levels. Floodplain wetlands require flooding to support the diversity and abundance of both waterbirds and woodland birds. Promoting dynamic flooding regimes in floodplain wetlands affected by river regulation will likely enhance bird diversity and their ecological and cultural values.