AN ASSESSMENT OF THE ACCURACY OF KANGAROO SURVEYS USING FIXED-WING AIRCRAFT

The use of line-transect methodology, on foot or from a helicopter, is likely to return the most repeatable, least biased estimates of kanga roo density. However, the associated costs make both methods impractic al for broad-scale surveys. For these, a fixed-wing aircraft remains t he most cost-effective platform. Limitations of the standard fixed-win g method (200-m strip transects) are well known, but it continues to b e used because it provides an index of trends, because there are now l ong runs of data (almost 20 years in some cases) collected in this sta ndard form and an alternative method is lacking. In this study, four v ariations of fixed-wing surveys of kangaroos were investigated: two li ne-transect methods (involving different scanning techniques), the sta ndard 200-m strip transect and a 100-m strip transect. Surveys using t hese methods were compared with helicopter line-transect surveys along the same flight lines in three areas (5000-7500 km(2)) in western Que ensland. Both fixed-wing line-transect methods failed to produce consi stently accurate estimates of density for all three species surveyed: red kangaroos (Macropus rufus), eastern grey kangaroos (M. giganteus) and common wallaroos (M. robustus). While generally more accurate than the uncorrected strip-transect counts, they were no less variable. Ho wever, the strip-transect counts still need to be corrected for bias f or which this study offers revised estimates of correction factors for eastern grey kangaroos (3.7-10.2) and common wallaroos (3.8-4.1), and estimates for red kangaroos (1.7-2.7) that support currently used val ues. An attractive alternative is to survey in 100-m strip transects, which offer improved visibility (correction factors of 1.0-1.8 for red kangaroos, 2.1-3.6 for eastern grey kangaroos and 1.7-2.1 for common wallaroos) and are therefore likely to be more accurate and repeatable . However, these advantages need to be assessed in relation to continu ing long runs of data using the standard 200-m strip transect. Correct ion factors for wallaroos are conservative as helicopter-based density estimates are known to be underestimates. Further work is needed to a ssess the generality of correction factors, both spatially and tempora lly.