Last Update: August 2000
Author: F. A. Leighton
Reviewer: W.M. Samuel (August 2000)
According to Mooring and Samuel (see reference list below), grooming behaviour in ungulates can be viewed as resulting from the combined effects of two different mechanisms. One mechanism is called "programmed-grooming". This is spontaneous grooming behaviour that occurs without any particular irritation or other stimulus. It is initiated by the central nervous system, similarly to the way that spontaneous breathing is initiated. The other mechanism is called "stimulus-driven grooming", and is grooming behaviour that occurs only in response to irritation. Some African ungulates that have been studied exhibit high rates of programmed grooming. It is thought that this behaviour may have evolved because of the year-round contact with ticks that these species experience. High rates of spontaneous, "programmed" grooming effectively remove ticks (be they larvae, nymphs or adults) that are newly arrived on the animal before these ticks can attach. Thus, programmed grooming is thought to be a protective behaviour that evolved in association with the constant presence of ticks.
Moose appear to have a low level of programmed grooming behaviour, while other North American deer, bison and elk have higher rates. These other species also may respond to tick larvae and nymphs as irritants, thus adding some degree of stimulus-driven grooming to the already significant rates of programmed grooming. As a result, these species remove tick larvae and nymphs by grooming before winter and thus are parasitized by a relatively small number of adult ticks in late winter and spring. In contrast, moose do not respond to larvae and nymphs as irritants, but are highly stimulated to groom only by adult ticks when they begin to feed in February and March. At this time, moose spend large amounts of time grooming and appear harassed by the large numbers of feeding adult ticks on their skin.
It is possible that moose do not respond to Winter Tick as do the other, less susceptible species discussed above, because moose are relatively new arrivals in North America, having arrived via the Bearing Sea land bridge from Asia. The Winter Tick is not present in Asia or elsewhere in the Old World. While the New World species of ungulate hosts evolved in association with Winter Tick, the moose did not. Thus, the grooming behaviour of moose is inappropriate as a defence against this particular parasite, and it can suffer severe disease as a result.
Too little is known about Winter Tick on caribou to allow one to test these ideas about grooming behaviour and zoogeography with data from this host species.
Mooring, M.S., & Samuel, W.M. (1998). Tick-removal grooming by elk (Cervus elaphus): Testing the principles of the programmed grooming hypothesis. Canadian Journal of Zoology. 76:740-750.
Mooring, M.S., & Samuel, W.M. (1998). The biological basis of grooming in moose: Programmed versus stimulus-driven grooming. Animal Behaviour. 56:1561-1570.
Mooring, M.S. and W.M. Samuel. (1998). Tick defense strategies in bison: the role of grooming and hair coat. Behaviour 135:693-718.