Accuracy of kangaroo survey
Abstract from Wildlife Research, 1998, 25, 315-326...
The most repeatable, least biased estimates of kangaroo densities are achieved using a line-transect methodology either on foot or from a helicopter. However the costs of these methods make them impractical for broad-scale surveys where a fixed-wing aircraft provides the most cost-effective platform.
Although the limitations of the standard fixed-wing method are well known, it provides an index of trends because there are now 20 years of data for some of the runs. This study looked at four variations of fixed-wing surveys of kangaroos and compared the results with helicopter line-transect along the same flight lines in three areas in western Queensland.
The four variations investigated were two line-transect methods using different scanning techniques, the standard 200 m strip transect and a 100 m strip transect.
Results: Neither line-transect method produced consistently accurate estimates of the densities of the three species surveyed (red kangaroo, eastern grey kangaroo, common wallaroo).
The 100m strip transect method worked well through improved visibility of the animals. However, these advantages are offset by the inability to compare the results with previous surveys using the standard 200 m strip transect method. The study produced revised estimates of the correction factors required to convert survey results to actual population densities.
Line transect - an observer counts all animals seen while the plane flies the 100 m path
Strip transect - an observer counts all animals seen within a previously determined distance (e.g. 10 m) of the flight path; if the strip is 10 m on either side of the flight path, then all animals seen within the 100 x 20 m strip are counted