Do Wild Reindeer Exhibit Grazing Compensation during Insect Harassment?

Abstract

We studied wild reindeer (Rangifer tarandus tarandus) to determine whether a wild ungulate can sufficiently increase its grazing time to compensate for loss of ingestion and rumination caused by insect harassment. We also tested the effect that insect harassment may have on autumn carcass weights. During summer 1997 and 1998, we recorded 24-hr activity budgets and frequency of change in activity bouts for wild reindeer. Following diurnal periods' insect harassment and decreased grazing, animals did not compensate by increasing grazing time or intensity during the night when insect harassment was low. Adult females and calves weighed significantly less in autumn 1997 following a summer of diurnal insect harassment, compared to autumn 1998 following a summer of little insect harassment. This indicates that the effect of daily insect harassment on activity budgets and grazing intensity had a negative effect on the body weights of adult females and calves. For reindeer, as for most wild ungulates, reduced body weight indicates poor condition and can jeopardize survival, reproduction, and calf recruitment.