Comparison of Surveys of Kangaroos in Queensland Using Helicopters and Fixed-Wing Aircraft.

Abstract

Kangaroo harvest quotas for each Australian state have been set mainly as proportions of population estimates derived from aerial surveys. Estimating population size from strip transect counts using fixed- wing aircraft has become an established technique, but counts must be adjusted by correction factors to ensure population estimates are both accurate and repeatable. Surveys of kangaroos in Queensland are currently conducted with helicopters using line transect methodology, but cost restricts their use to relatively small survey blocks. Nevertheless, they return more accurate and repeatable estimates of kangaroo density than surveys with fixed-wing aircraft. A comparison of the above two techniques was made along the same transect lines in seven survey blocks (5000-10,000 km2) in southern and western Queensland, allowing an assessment of the comparative accuracy of the fixed-wing method. For red kangaroos (Macropus rufus), required correction factors of 0.7-3.1 were similar to those used previously. However, for eastern grey kangaroos (M. giganteus), substantially larger correction factors of 3.4-10.2 were needed to approach true density. For wallaroos (M. robustus), correction factors of 3.8-4.8 were required, but can be considered conservative because helicopter-derived density estimates are known to be underestimated by a factor of 2-3. Further work is needed to establish how correction factors for each species should be applied on a broader scale and whether they lead to repeatable estimates of kangaroo density. Key words: aerial survey, line transect, correction factors, strip transect, wallaroo.