Patterns in the decline of granivorous birds in the Northern Australian savannas

Abstract

Several granivorous bird species of the northern Australian savannas are known to be threatened and others are suspected to have declined. However, for most species there is little documented evidence such that the generality of the problem is uncertain, and the mechanism(s) for change are unclear. In this thesis, I seek to determine the taxonomic and geographic scope of the problem and identify ecological, spatial and temporal patterns of decline which may shed light on its causes. To do this, I compiled a database of over 60,000 historic records of granivorous birds, which I analysed for changes in distribution and reporting rates. Analyses of reporting rates were controlled for historic shifts in the geographic distribution of records, and for change in search effort. To provide context for these analyses, I also examined biogeographic patterning in the Australian granivorous bird fauna using data from the Atlas of Australian Birds.

The granivorous bird assemblages of the northern Australian savannas are diverse. They are especially rich in terrestrial-foraging finches and pigeons, but support few arboreal-foraging species. Rates of regional endemism are particularly high, and many of the endemics have restricted distributions within the savannas. At least twenty of fifty-nine species have changed in abundance since European settlement, and most of these (17 species) have declined. Declining species share a marked propensity to forage exclusively on the ground or amongst herbage, but all increasing species and many species for which no change in abundance was demonstrated also share this habit. Decline has been most severe in central Queensland; moderately severe through much of the remainder of Queensland(excepting Cape York Peninsula) and in inland areas of Western Australia and the Northern Territory; and least in the north Kimberley, the Tiwi Islands and eastern Arnhem Land. In southern and central Queensland, the only part of northern Australian savannas subject to extensive clearing of native vegetation, the decline of granivorous birds was associated with the pastoral era prior to the commencement of clearing.

The northern savannas have suffered a major loss of biodiversity. Its causes are unclear, but are probably related to the direct or indirect impacts of pastoralism and the loss of Aboriginal landscape burning on food resources. Further research is required to determine its causes and develop management strategies.

Date of Award	1998
Original language	English
Supervisor	Richard Noske (Supervisor)