The conservation status of birds in arid Australia.

Abstract

The impression has been given in previous studies that there are few bird conservation problems in the arid zone, particularly because not one of a total of 230 species has become extinct. In stark contrast, almost half of the native terrestrial mammalian fauna of the Australian arid zone has become extinct on the mainland since European occupation. Here we show that the status of one half of the avifauna has changed since European occupation, and conclude there are many threats to avian biodiversity at the regional scale in the arid zone. There are 19 species (8%) in the arid zone classified as rare and threatened nationally. Twelve more (5%) are uncommon species which have declined or are at risk in two or more regions. A further 40 species (17%) have declined in at least one arid region, although many of these remain common and some have increased elsewhere in arid Australia. At least 45 species (20%) have increased in range or abundance, including a suite of ground-feeding birds associated with degraded landscapes. Striking patterns emerged from analysis of 29 threatened and declining species: • birds associated with chenopod shrublands and grassy, riparian or floodplain environments have been most affected whereas mulga inhabitants and canopy-dwellers of riparian woodland have been little affected; • birds generally with a northem distribution have declined in the south of the arid zone and birds with a southern distribution have declined in the north of the arid zone, and these patterns contrast with many birds with a southern or continental distribution which have declined more in southern semiarid regions than within the arid zone itself; • birds which feed at ground and low shrub height have been most adversely affected; • sedentary bushbirds (passerines) are more at risk than nomads and their limited mobility seems to be a risk factor; • among non-passerines, parrots, cockatoos and pigeons are most at risk, while three passerine families stand out, namely wrens, quail-thrushes, and thornbills and allies; • contrary to findings for mammals, size does not generally appear to be an important risk factor. Land degradation and habitat alteration such as shifts in abundance or dominance of plant species caused by the introduction of exotic herbivores appear to be the principal factors causing change in status while the provision of reliable water sources in pastoral districts is also important. Introduced predators are implicated in some cases and altered fire regimes may have played a part in spinifex and mallee habitats. Competitive interactions between increasing and declining species, although not demonstrated, appear to be likely for some species. We have documented a hitherto unsuspected degree of change in avian biodiversity in the Australian arid zone. In the absence of widespread regeneration of dominant plant species in the southern arid zone, the decline of many arid zone birds will accelerate dramatically. Also, unless better management ensues, the next major drought could cause accelerated declines and extinctions. We advocate a range of measures designed to improve the conservation prospects for arid Australian birds, including lower stocking rates on pastoral properties, rehabilitation of critical habitats and their protection from exotic herbivores, experimental research on the impact of grazing and predation, and monitoring of both threatened species and a range of sedentary passerines typically associated with representative habitats in the arid zone.