Re: Estimating Fox abundance through scat analysis

Phil - My colleague, Katie (who works on carnivores) had the following advice:

“I would in general say it is hard to get any accurate estimates of abundance without conducting a systematic survey, which is often labour and time intensive. So walking the dog and counting scats [dung] probably wouldn't be sufficient to do that. Furthermore carnivores are probably one of the hardest animal groups to survey because they are often cryptic [camouflaged], nocturnal, occur at low densities and within a range of social systems. As a result though a lot of indirect methods have been developed to assess their abundance - many of which involve estimations using scat.

There are two ways in which scat is often used to calculate indexes of abundance: 1) quantifying the “standing crop” i.e. total amount of faecal material in a given area 2) quantifying the accumulation rate (monitoring the rate of defecation in fixed sample plots in a way that fresh additions can be accurately counted).

There are many factors that could introduce errors into these estimates, such as seasonal variation in defecation, scent marking, fecal weathering, territoriality and these should be considered in any later analysis. Ways of reducing/ avoiding these biases are listed in the Wilson and Delahay paper below.

The red fox survey of great Britain applied the technique of measuring rates of fecal accumulation at a National level. See http://www.wbrc.org.uk/WorcRecd/Issue7/ruralfox.htm for details. It was conducted in association with the Mammal Society and I am sure following their technique would make your estimates comparable to those already carried out. In fact they probably have an index which you could then extrapolate your counts from to give you a better idea of actual numbers of foxes. The Mammal Society is a really informative and helpful society and I am sure could provide a lot more information on this subject especially the results and conclusions of their surveys using this technique. There are definitely a lot of problems associated with using fecal counts but I think you are in a rare position that a lot of work has already been carried out countrywide regarding this technique for the animal you are interested in, so with a bit of luck someone has already evaluated those problems and will be able to advise you on how to avoid them etc.

Check out the mammal society web page, and the red fox survey results, http://www.abdn.ac.uk/mammal/newsite/index.shtml and go to the link to the red fox survey or directly go on this address: http://www.abdn.ac.uk/mammal/foxsurv.htm (check the map for other counts in your county)

I would recommend a couple of specific papers for more info:
G.J.Wilson and Delahay, R. J. 2001. A review of methods to estimate the abundance of terrestrial carnivores using field signs and observation. Wildlife Research 28: 151-164
Cavallini, P. 1994. Faeces counts as an index of fox abundance. Acta Thereologica 39: 417-424 http://www.wbrc.org.uk/WorcRecd/Issue7/ruralfox.htm