Pine Marten Red Fox interactions – a case of intraguild predation.

We pursued the hypothesis that pine martens (Martes martes L) suffer from intraguild predation by red foxes (Vulpes vulpes L). An increase in population density of pine martens in Scandinavia was observed concominant with a decline in the number of foxes due to an epizootic of sarcoptic mange during the 1980's. The increase was noted both as numbers of crossing marten tracks on snow along transects in a lokal area, and as numbers of martens harvested in Sweden. The latter could be linked county-wise by timing and amplitude to the ocurrence of mange and decline of number in foxes harvested. We also compiled 16 cases of casually observed predation by red foxes on martens, and calculated a yearly mortality rate due to fox predation of 0,13 from>14 transmitter years of 26 collared martens in three areas of Scandinavia during the period of high marten numbers. We conclude that the case against the fox is strong.publishedVersio