Spatial and Temporal Variations in Hydraulic Habitat in a Complex Floodplain-wetland System

The provision of suitable hydraulic habitat is essential for successful colonial waterbird breeding in ephemeral wetlands. Two aspects of hydraulic habitat of are particular importance. An inundated area of sufficient depth (typically greater than 1 m) and duration (typically greater than 3 months) for areas utilised by water birds for breeding. Provision of this habitat allow for juvenile birds to successfully fledge whilst remaining protected from land based predators. A sufficient inundated area of shallow depth (typically less than 25 cm) is also required as feeding habitat. In this study we investigate the temporal and spatial patterns in the provision of these two key waterbird requirements and relate them to known waterbird breeding events in the Narran Lakes, Australia. The Narran System, with two individual wetland systems and a series of interconnecting channels represents an ideal site for maximising these two essential hydraulic conditions. The results of this study show that the two lakes are very different in terms of their hydraulic character and these differences are magnified when the temporal component of wetting and drying is considered. However, as a collective, they provide the essential functions of breeding and feeding habitat. The northern wetland of the Narran System is the main provider of breeding habitat while the southern wetland provides abundant feeding habitat. The spatial complementarity of habitat providing different functions is the key to the importance of this water bird refugia. Maintaining the hydraulic complexity of the Narran System, as an asset capitalized upon by colonial waterbirds, must be recognised in any water management plan for this system.