Download files
Abstract
Considerable knowledge gaps remain in our understanding of the response of waterbird communities and population dynamics in response to flows in floodplain ecosystems. Conservation of inland wetlands relies on the effective management of environmental flows for flood-dependent biota, including waterbirds. I investigated how waterbird communities responded to a flow pulse in the Macquarie Marshes, an internationally recognised (Ramsar-listed) wetland. Two environmental flow pulses were released in early September (4,882 ML) and mid-October (28,911 ML) and four survey periods (1-4) occurred in August, October (before the 28,911 ML flow), December and January. I surveyed waterbirds at 17 sites before (August, October), during (December) and after (January) the larger of two environmental flow releases (totalling 33,793 ML in 2014-15). I compared waterbird response to flows across three wetland types: channels, lagoons and floodplains. I used generalised linear models to test for the effect of flow and other environmental variables on total waterbird relative abundance and number of species and for each functional or taxonomic response group: ducks, herbivores, large waders, piscivores and shorebirds. Duck counts for all surveyed wetlands were highest in survey period 1 (48± SE 20.29), herbivores in survey period 2 (3.71±0.11), large waders in survey period 3 (11.75±8.81), piscivores in survey period 4 (2.69±2.18) and shorebirds in survey period 2 (11.41±5.88). Wetland type and local inundation had a significant effect on waterbird abundance and the number of species at all sites and survey periods, with lagoons and floodplains supporting the highest numbers. Lagoon and floodplain sites were standardised (4 ha) area, to allow comparisons in waterbird density. To determine whether waterbird behaviour varied with resource availability following a flow pulse, I separately modelled the number of birds engaged in one of three behaviours (feeding, locomoting, roosting) per functional group, as a proportion relative to the other behaviours at a site. Lagoons supported the greatest proportion of feeding waterbirds, with a high proportion of large waders (0.60±0.12), while floodplains had large proportions of locomoting large waders (0.40±0.09) and shorebirds (0.55±0.12). Channels had limited foraging habitat, but provided roosting opportunities for waterbirds, especially piscivores (0.10±0.05). I also collected macro-invertebrate samples at floodplain and lagoon sites and found the proportion of ducks feeding was positively associated with macro-invertebrate (prey) biomass. The feeding activity (number of actions per 1-minute) of two common species (yellow-billed spoonbill Platalea flavipes and black-winged stilt Himantopus himantopus) was strongly positively correlated with lagoon wetlands. This study identifies site-specific variables (local inundation and wetland type) as important drivers of waterbird abundance. Lagoons supported the greatest relative abundance of waterbirds as well as the highest proportion of feeding activity. This study supports the release of environmental flows to create and maintain habitat for waterbirds, during a relatively dry season. Further understanding of the spatio-temporal dynamics between waterbird functional groups, flow and other environmental variables would assist in the development of measurable targets to sustain waterbird feeding habitat.