Foraging behaviour of captive black-tailed deer (Odocoileus hemionus columbianus)

A review of the literature on black-tailed deer (Odocoileus hemionus columbianus Richardson) feeding habits reveals considerable variation among animals, locations, and seasons. Processes affecting food selection, however, are poorly understood. Optimal foraging theory was explored as a means of predicting deer foraging behaviour and diet breadth. Because of complex constraints and objectives involved in predicting diet selection, food preference was determined under ad libitum conditions. Feeding behaviour of two deer was studied in a 0.5-ha enclosure to examine the effects of density and distribution of their preferred foods on diet selection. When deer had to search for food, diet selection remained the same as that under ad libitum conditions as long as preferred food was abundant. Deer nearly exhausted their highly preferred food before switching to lower ranked foods. This switch was gradual, as deer continued to search for preferred food. The amount of preferred food already eaten during a trial was positively correlated with the time that animals would continue searching before switching to lower-ranked foods. Switching was related to the amount and type of food encountered and not to the amount of food in the pen. Dispersion of the preferred food (clumped versus unclumped) had no significant effect on the amount of food eaten, but did significantly influence the types of food encountered by one of the two animals. Both animals became more efficient (intake per distance travelled) at finding preferred foods with increasing experience with a specific distribution of food. Animals increased their efficiency of finding apples by repeating searching patterns which had been effective during previous trials. Performance was poor, however, when distributions were changed. When preferred food was abundant, platforms containing preferred food were not always completely cleared of food the first time a platform was visited. Intake rates of non-preferred foods tended to increase with declining abundance of preferred food. This increase was not caused by changes in the amount of non-preferred food eaten at feeding stations, but rather by the rate at which non-preferred feeding stations were visited. The influence of intraspecific plant variation on food habit studies and the utility of preference indices are discussed. I conclude that foraging bouts are highly dynamic and that some foraging questions may not be adequately answered if this internal variation is ignored.Forestry, Faculty ofGraduat