Rutting behaviour in reindeer ( Rangifer tarandus L.)

Abstract

This paper deals with rutting behaviour in two groups of reindeer studied at the Reindeer Research Station in Swedish Lapland. The first visible signs of rutting behaviour are described as well as the establishment of the harem and its ruler. Old bulls copulate more often than younger ones owing to the earlier occurrence of rut in these, their stronger fighting ability and the fact that old bulls are more polygamous than their younger rivals. The chasing away of intruders, and the constant herding of his own herd, keeps the ruling bull very active. Since, furthermore, he does not eat he becomes very thin during the rutting season. The size of the area necessary for a harem varies. A big bull with a large harem is able to keep his rivals away from a considerably greater area than a young bull with a small number of cows. The rutting territory seems not to be defined by particular geographical boundaries, but is an area, which changes with the movement of the harem and has no topographical references. The author has observed nothing that indicates territory markings in the proper sense, but the bull urinates on his hind legs, especially at threatening and exciting moments, and this behaviour may be interpreted as a form of territory marking. The rutting sound of the bull is a series of husky, rapid, rather low-voiced rattles that are brought about by the air being repeatedly pressed out of the lungs. The sound differs slightly from that made when the bull is driving in the immediate vicinity of a cow. Threat behaviour has been described as well as overflow activities resulting from a high level of aggressive behaviour. A typical rutting behaviour, that could be characterized as courting, is the bull's driving of the cows, i.e. the bull's running or walking after a cow depending on her heat status. Aggressiveness on the part of the ruling bull is more evident against older rivals than against younger ones, and old cows are particularly aggressive against young bulls. The first copulations usually take place during the last days of September. Mating activity reaches it peak at dusk and at dawn. Copulation seems to take place only once with each cow. The heat development of the cow has been described as well as the copulation act.