COMPARISON OF HELICOPTER LINE TRANSECTS WITH WALKED LINE TRANSECTS FOR ESTIMATING DENSITIES OF KANGAROOS

The performance of helicopter surveys for estimating population densit ies of red kangaroos (Macropus rufus), eastern grey kangaroos (Macropu s giganteus) and common wallaroos (Macropus robustus) was investigated by comparing line-transect density estimates obtained from helicopter surveys with those from ground (walked) surveys. Comparisons were mad e at four sites in central western Queensland (areas with high densiti es of red kangaroos and common wallaroos) that were surveyed during wi nter and summer from December 1991 until February 1995, and one site i n south-eastern Queensland (an area of high eastern grey kangaroo dens ity) surveyed annually during autumn from March 1991 until March 1994. Helicopter surveys generally recorded lower sample sizes than did gro und surveys (means +/- s.e = 34 +/- 6%, 33 +/- 9% and 76 +/- 2% lower for red kangaroos, eastern grey kangaroos and wallaroos, respectively) . Density estimates obtained from the helicopter surveys were not sign ificantly different from those obtained from ground surveys for both r ed and eastern grey kangaroos as assessed by repeated-measures ANOVA a nd regression analysis. However, helicopter surveys of common wallaroo s consistently returned density estimates about half those of ground s urveys. The relationships between the two methods did not differ betwe en winter and summer for any species. The conventional aerial survey m ethod for kangaroos of strip transects from fixed-wing aircraft has li mited ability to adjust for varying sightability conditions. Therefore , helicopter surveys with line-transect sampling are an attractive alt ernative.