Different tracking techniques
Tracking Bilbies, Bridled Nailtail Wallabies, Numbats and Stick-nest Rats
While trapping is a good technique for measuring Boodie and Woylie populations, it is not useful for generating meaningful population size estimates for Bilbies, Bridled Nailtail Wallabies and Numbats.
None of these species are readily captured in traps. Accordingly, AWC uses a technique called “distance sampling” to estimate population size.
This involves driving a set route around Scotia recording all of the animals that are seen. When an animal is seen, we record the distance it is from the track. The data we collect is then fed into a computer program, which applies some complex calculations involving change in ‘detectability’ with increasing distance from the track in order to estimate population size.
Employing this method, we estimate there are over 150 Bridled Nailtail Wallabies in Stage 1, plus a population of more than 500 additional Bridled Nailtail Wallabies in Stage 2 and other areas. To verify this technique, we have compared Boodie population size estimates generated by trapping versus by distance sampling - the two methods produce almost identical estimates.
Similar estimates for other species also give us confidence that AWC’s conservation management actions are successful. We estimate we have over 600 bilbies in Scotia’s two feral free stages. Similarly, the Numbat population in Stage 1 is estimated at around 30 individuals and has persisted for almost 20 years at Scotia.
Tracking the Greater Stick-nest Rat population on Scotia however presents its own unique challenges. Stick-nest rats won’t enter the cage or pitfall traps and they are rarely ever observed. To counter this, AWC has initiated a program of nest surveys whereby a large group of people walk a grid through the Scotia Mallee searching for the characteristic stick nests this species constructs. Three nests have now been mapped on Scotia. This is exciting as each nest is thought to hold up to 20 individuals.
The data derived from AWC’s population estimates informs our management decisions and enhances our effectiveness in securing the future of six of the world’s rarest species.
Population estimates of Bridled Nailtail Wallabies (BNTW) at Scotia. The populations in Stages 1 and 2 are estimated via distance sampling, whereas the captive population is estimated by a direct count during feeding.
Please help AWC’s project to secure the future of six of Australia’s most endangered mammals, including the Bilby, the Woylie, the Bridled Nailtail Wallaby, the Boodie, the Numbat and the Stick-nest Rat which find refuge at Scotia.