The relative roles of body size and feeding type on activity time of temperate ruminants

Recently, there has been some critical testing of whether body size or feeding type (CS: concentrate selectors, IF: intermediate feeders, GR: grass-roughage eaters) is the most important determinant of physiological aspects of ruminant ecology, whereas little has been done on behavioral aspects like activity time. Different predictions regarding the relationships between activity time and body weight/feeding type were tested with activity time data from 18 temperate ruminants. Activity time decreased allometrically with increasing body weight, but there was also a tendency for an effect of feeding type. Exclusion of one statistically defined outlier (mountain goat) made the effect of feeding type highly significant. GR and CS were about equally active. Surprisingly, IF were more active than both GR and CS. The hypothesis is put forward that IF are more active than GR/CS due to their opportunistic use of high-quality forage of both types (concentrate and grass-roughage; on average better quality and hence shorter rumination time), though possible confounding effects of observation methods and varied behavior with respect to cover among CS, IF, and GR should also be evaluated. Received: 22 May 1997 / Accepted: 22 September 1997