Tick-removal grooming by elk (Cervus elaphus): testing the principles of the programmed-grooming hypothesis

Abstract

The grooming behaviour of elk (Cervus elaphus) was observed in order to test the predictions of the programmed-grooming hypothesis. The highest grooming rates occurred when most winter ticks, Dermacentor albipictus, were blood-feeding. Elk at Elk Island National Park (EINP) and Jasper National Park (JNP) oral-groomed most during October-November, when larval ticks were engorging, with a secondary peak of grooming occurring during February-March-April, when nymphal and adult ticks were engorging. Elk at JNP supported 3 times the density of ticks and groomed 2-4 times more frequently than elk at EINP. Extensive grooming resulted in hair loss on JNP elk, with highest prevalence of hair loss in months with high grooming rates. These results support the prediction of the "tick-challenge principle" that hosts will groom more frequently when the threat of tick infestation is greater. At JNP, calves 1-6 weeks old groomed at 6-10 times the rate of cows, supporting the prediction of the "body-size principle" that smaller animals will groom more than larger animals. These patterns of grooming in elk may reflect an intrinsic grooming clock selected to optimize the tick-removal benefits of grooming in accordance with the constraints imposed by the Canadian winter.