THE EFFECT OF WOLF PREDATION AND SNOW COVER ON MUSK-OX GROUP-SIZE

I examined the pattern of seasonal and regional differences in musk-ox group size with respect to the costs and benefits of avoiding predation and acquiring food. In winter, group sizes were about 1.7 times larger than in summer. Variation in group size among areas was related to wolf densities in both seasons. Seasonal differences in group sizes were related to winter snow cover probably because snow renders feeding sites less abundant, increasingly patchy, and more ephemeral. Group size appears to be a trade-off between increasing per capita benefits of decreased predation risks in larger groups at higher wolf densities, lower per capita benefits of group foraging in summer than in winter, and higher per capita crowding costs as group size increases. The musk-ox breeding system does not influence group size but simply makes do with group sizes determined by ecological factors.