Do parasite burdens in spring influence condition and fecundity of female mountain hares Lepus timidus?

Mountain hare Lepus timidus populations show unstable dynamics with regular 7-10 year fluctuations in abundance. We tested the hypothesis that parasites destabilise hare dynamics by experimentally reducing parasite burdens and recording female body condition and fecundity. We trapped and radio tagged 42 female hares in April 2000 and 2001 in the Central Highlands of Scotland. Of these, 23 were treated with Ivermectin to remove intestinal parasites and 19 were left untreated as controls. The treated and untreated hares were killed in October together with a second control group of 19 unhandled hares. Treatment with Ivermectin reduced the abundance of the parasite Trichostrongylus retortaeformis and increased the body condition of hares. There was a trend for increased fecundity in treated hares, but this was not statistically significant. Our study demonstrates that parasites can reduce mountain hare condition and may affect their fecundity. We conclude that a host-parasite interaction is a possible mechanism for destabilising mountain hare dynamics.