19 September 2013 Tagging technology tackles possums

Kiwi ingenuity combined with forensic science techniques has produced a method of identifying individual possums that has the potential to also be used in the fields of environmental and human science.

Dr James Ross  from the Centre of Wildlife Management and Conservation at Lincoln University is using a locally-developed, activity interference device (WaxTag®) baited with attractant substances to identify individual brushtail possums biting the tags.

In the absence of an efficient and cost-effective alternative to estimating the abundance of possums after control methods have been applied, the residual trap-catch index (RTCI) remains the monitoring standard at present. However, RTCI is not sensitive in locating survivors when the population is at very low densities and it is costly because traps need to be checked daily.

Dr Ross’ research aims to find out whether any survivor possums are present in a given area and how many individuals are there.

The v-shaped plastic WaxTag® are attached near the bottom of tree trunks by staples and either loaded with attractant bait (peanut butter works best) or with an attractant blaze of flour and icing sugar above. The possums bite the tag leaving teeth marks and saliva.

Initially, when using the WaxTag® bite marks could only show whether possums were present or not, but not how many individuals as the same possum could bite a succession of tags. When combined with molecular biology techniques such as DNA analysis from saliva, the power of the technique was revealed.

Dr Ross is now testing the sensitivity of an optimised DNA protocol in comparison with previously collected ear-tissue extracts to assess whether the DNA collected from WaxTag® is of a high enough quality and quantity to yield reliable genetic profiles of individual possums.

“From a monitoring perspective, it is important to know whether one possum has bitten one tag or several tags in a line in order to get an accurate population estimate to help plan future control measures,” says Dr Ross.

“For New Zealand, on-going improvements in possum management mean a greater potential to eliminate bovine TB from the mainland and this protects our valuable overseas markets for beef, venison and dairy products. A reduction in possum numbers also means that the remaining areas of native forest are better protected enabling the recovery of many endangered plant and bird species,” says Dr Ross.

For more information, read the full article on page 21 of the University’s research profile publication Transform.