Possum poo gives clue to possum numbers
Researchers have found a new way to assess possum numbers * through checking their individual calling cards, or in other
words, possum poo.
Possums wreak havoc on native bird and plant life, and spread bovine Tb. To help manage the threat to biodiversity and
contain Tb, good information is needed on the number of possums surviving following a control operation. Although this
number is usually small, it drives subsequent population recovery.
At present, official estimates of survivors are based on the number of possums caught in leg-hold traps.
However, this method is expensive and time-consuming, and results are biased where possums have become trap-shy or, for
some reason, do not encounter traps.
In a project funded by the Animal Health Board, Landcare Research scientists have found a way to extract DNA from possum
droppings. They can then use the unique genetic profiles obtained from possum droppings to identify individual possums
and estimate numbers of possums that are not killed or caught. The method is the first step to an unbiased way to
determine exact possum numbers.
" Because in some instances there are possums that you cannot hunt or trap easily, it's difficult to estimate how
effective a control operation has been," says the project manager, Graham Nugent. "Possums produce more than 100 small
droppings a day, so you have much more chance of finding possum poo than finding possums. And of course, possum poo
doesn't try to hide from you. "Our research shows that you can extract DNA from droppings anywhere up to 27 days old,
depending on how much rain there has been."
Mr Nugent says this technique for counting elusive wild animals may prove to be one of one cheapest when the animals are
scarce. "That's because only a few DNA samples are needed to 'capture' some of the possums at least twice when there are
only a few animals. It is the proportion of recaptures that is used to estimate possum numbers."
Landcare Research geneticist Dr Dianne Gleeson says although examining possum poo is hardly glamorous, the results have
been very exciting.
"We did not expect to have any success. However, by peeling the 'skin' off the droppings with a scalpel, we could find
small numbers of DNA cells that have been sloughed off the walls of the possum's gut.
"With this approach, we gain enough information to obtain individual genetic profiles of possums that remain at large."
Dr Gleeson says the cost of the technique compares well to field counting methods, and will decrease as procedures are
further streamlined. She says researchers can immediately start to use the technique as a tool to estimate possum
numbers.
However, and perhaps unfortunately for her, this success has sparked similar projects. "We are now working with deer
droppings, to see if they can yield clues to numbers in the wild. But there are plans to extend this to wild pig poo.
"Deer and possum poo is bearable, but pig poo is pushing the limits of what we can tolerate."