Using two populations of sika deer Cervus nippon, the relationship between tick density within habitats and the duration of both self-grooming and allogrooming was investigated. At Mageshima Island, where the deer spend much of their time feeding and tick density is high, the time spent self-oral grooming frequency fluctuated with tick density within the deer's habitat. However, in Nara Park, where the deer are fed artificially and tick density is low, neither oral nor self-scratch grooming correlate with tick density. Although tick density is much higher at Mageshima than at Nara Park, the overall duration of self-grooming did not differ between these sites, suggesting that this was affected by the time budget required for other behaviors, especially foraging. Allogrooming duration did not correlate with tick density at either study sites, suggesting that the most important function of this behavior is a social one, rather than the removal of ectoparasites.