Document: CHR-3-50-10

Vigilance, feeding efficiency, and optimal group size of northern bobwhite coveys.

WILLIAMS, C.K.* ¹, R.S.LUTZ ¹ and R.D.APPLEGATE ²

University of Wisconsin, Madison, WI 53706 USA ¹
Kansas Department of Wildlife and Parks, KS USA ²

Abstract:
Numerous studies of birds and mammals have proven that group size negatively correlates to the amount of time individuals scan for predators. Because individuals in larger groups spend less time in vigilance, they can feed more efficiently. Northern bobwhite (Colinus virginianus) form social units (called coveys with an average size of 11) during the non-breeding season, however little is known about their advantages. Consequently, we tested these relationships and examined whether these behaviors promote an optimal covey size. To observe the effect of differing group size of feeding/vigilance behavior, we created artificial covey sizes (4, 8, 12, 16, and 20) in a semi-natural yet closed environment with both escape cover and an open feeding area. With the aid of a video camera, we recorded the amount of time individuals had their heads down (feeding or non scanning behavior) and the amount of time they have their heads up (scanning behavior). Additionally, we presented a raptor silhouette to record the time it took for the group to notice this potential threat, therefore indexing the overall vigilance of the group. Results indicate that as group size increased, they spent more time feeding in the open area (P = 0.01). Group size had no influence on the per cent of the covey that had its head up (P = 0.81). However, an increase in group size was positively correlated to the overall vigilance of the group (P = 0.02). Additionally, larger groups improved the odds of detecting a predator (P = 0.02). Therefore larger groups enjoyed greater awareness of predators but at a cost of less efficient feeding. Smaller groups appeared to feed more efficiently but had lower predator vigilance.

Keywords: Group size, northern bobwhite, vigilance, feeding efficiency

This abstract is being presented at: 11:15 AM in session:
Oral Session #3: Avian Ecology.