What does the fox (scat) say?
For a few years now the CEC team has been walking long-distances on transects though the Otways picking up every fox scat (poo) we see along the way to try and determine whether the Otway Ark fox control program is reducing numbers of foxes.
The most basic analysis we do is to compare the number of scats found before and after baiting at one site that is baited, and one that isn’t, which controls for other effects, such as the weather. We do this on the assumption that the number of scats we find scales with the number of animals in the landscape. In other words – more scats should equal more foxes. A straightforward, yet often invalid assumption.
But recently we got fancy, thanks to funding provided by the Wettenhall Environment Trust and Helen Macpherson Smith Trust, and were able to send some of the scats away for genetic analysis.
And we got some interesting results.
The activity index (number of scats per survey) was highly variable through time and suggested the control programme reduced fox activity in the baited area when compared to the non-baited area.
In contrast, the genetic sampling and spatially explicit capture–recapture analysis suggested fox density varied little throughout the study, with any changes unable to be attributed to the baiting programme. Additionally, because genetic sampling allows us to actually identify individual foxes, we confirmed many individuals persisted through seven months of baiting.
So, as we often need to say in science, “further investigations are required” as to what the most appropriate methodology might be. Activity indices can be quick and cheap to produce, but we need to make sure that they accurately reflect changes in the number of animals in the landscape before we can trust them implicitly.
Our study serves as a cautionary tale when it comes to using activity indices that have not been validated to guide land management decisions and demonstrates the value in adopting innovative approaches like genetic sampling.
Read the paper:
Mark N. Le Pla, Emma K. Birnbaum, Matthew W. Rees, Bronwyn A. Hradsky, Andrew R. Weeks, Anthony Van Rooyen, Jack H. Pascoe. Genetic sampling and an activity index indicate contrasting outcomes of lethal control for an invasive predator. Austral Ecology 47 (5) https://doi.org/10.1111/aec.13182