Monitoring the effects of feeding in groups: Behavioural trials in farmed elk in winter

Abstract

We studied the effect of managing group size in domesticated elk in the context of social foraging theory, and toward recommendations for livestock well-being and efficient use of common pastures. We compared foraging in adult female elk presented with feeding trays of alfalfa pellets mixed with segments of plastic tube. As the ratio of alfalfa pellets to plastic tubes decreases, there is a point called the giving-up density (GUD), measured as the weight of remaining food, at which a foraging elk stops searching for pellets. We compared individual scanning rates, or vigilance, as well as GUDs, over trials in repeated measures that included single elk and elk in groups of two, three, four, five, seven, 10, 13 and 17. We also compared a group of four and a group of seven elk with and without their calves, and groups with and without a dominant individual, defined as a female that moved to a feeding tray and resulted in its being abandoned by another female. We found an exponential decline in GUDs with increasing group size (F1,117 = 5.14, P = 0.02) regardless of presence of calves and consistent with the ‘group size effect,’ which predicts lower individual vigilance with a greater number in a group, a welfare benefit of social foraging. Among 10 adults tracked as focal animals through at least three trials, all but one elk expressed lower GUDs in larger groups, leading to 14% less scanning with each additional elk individual in a group (F1,117 = 8.42, R2 = (118 repeated measures) = 0.60, P < 0.01). With the exponential decline in both GUDs and scanning rate, we conclude that captive elk experience greater security as group size increases. Contrary to predictions from free-ranging elk, GUDs were significantly lower with calves present for the two group sizes compared (group of four, F1,32 = 17.1, P < 0.01; seven, F1,29 = 111.2, P < 0.01). With or without calves, neither scanning rate (F1,59 = 2.34, P = 0.13) nor the relationship of scanning rate with group size (F2,59 = 1.34, P = 0.25) changed. Separating dominant elk did not produce any significant effects. Pasture configuration to foster closer groups of elk could promote a healthier herd and more effective use of foraging areas. Farmers should manage elk groups to include calves with their dams whenever possible.