Western grey kangaroos, Macropus fuliginosus, in the South Australian pastoral zone: populations at the edge of their range

As part of a large-scale monitoring program linked to the management of kan garoos in the South Australian pastoral zone, the western grey kangaroo pop ulations have been surveyed annually with fixed-wing aircraft over the 15-y ears-period 1978-92. Western grey kangaroos are restricted in their distrib ution to the southern regions of the pastoral zone. During the period of th e study, western grey kangaroo numbers showed no long-term trends, but did show some marked fluctuations, principally in association with a severe dro ught. Despite this, and unlike red kangaroos in the South Australian pastor al zone, no consistent, direct association between changes in western grey kangaroo numbers and antecedent rainfall could be demonstrated. The postula ted reason for this is that most of the regional western grey kangaroo popu lations examined in this study were low-density populations at the edge of the range of this species. Outside of drought, these populations are likely to be limited by factors other than food, such as climate and unmodified r esources in the form of suitable habitat. Also, because boundary population s may well only be maintained by constant loss and recolonisation, local ex tinctions associated with drought may result in extended delays in the re-e stablishment of populations in marginal areas. Over the period 1978-92, the se populations were harvested commercially at annual rates of 5-25%, which were, on the whole, considered to be below the rates suggested to be maximu m and sustainable.