Woodland bird declines in the Murray-Darling Basin: Are there links with floodplain change?

Woodland bird population declines in Australia have been attributed to various factors including habitat loss, fragmentation, and degradation. However, the influence of altered water availability in the landscape upon woodland bird populations has not been examined, particularly in terms of changes in flood regimes and subsequent loss of floodplain productivity. In this review, we examine the importance to woodland birds of floodplains, floods, and associated vegetation communities, highlighting potential links between declining water availability, habitat degradation, and bird populations. Floodplain woodlands and forests may be important refuges for woodland bird populations because (1) floodplain woodlands and forests comprise some of the largest and most continuous vegetation remnants in south-east Australia; and (2) floods intermittently supply water, sediment and nutrients that drive greater primary and secondary productivity than found in woodlands not subject to flooding. However, floodplains in south-east Australia have been subject to substantial flow regime change, driven predominantly by dams and irrigation water use. Consequently, habitat quality for woodland birds has been degraded, potentially exacerbating population declines. We suggest that despite such change, floodplain communities and their requisite floods remain of great importance for the persistence, productivity and diversity of woodland birds in Australian drylands. We hypothesise that (1) the influence of flooding upon primary and secondary productivity in floodplain and riparian zones is a key driver of resident bird populations, and a key determinant of nomadic/migratory bird use of a site; (2) alterations in flooding and consequent changes in productivity and condition of floodplain vegetation have contributed to observed declines in resident woodland birds in Australian drylands; and (3) the influence of flooding upon productivity extends beyond local populations of floodplain residents to non-floodplain populations via dispersal, and that floodplain woodlands often act as a source population for surrounding non-floodplain woodlands. We make several testable predictions regarding these hypotheses.