Black-tailed deer feeding bouts: dynamic events

Foraging bouts of captive black-tailed deer (Odocoileus hemionus columbianus Richardson) were investigated to examine how searching for food affects diet selection. We determined food preference for three types of food under ad libitum conditions and then studied the foraging of two deer in a 0.5-ha, vegetation-free pen in which we controlled food availability and distribution of the same three types of food. Our hypotheses included the following: (i) clumping of preferred food into patches would enable animals to better exploit food distributions; (ii) the switch from preferred to lower-ranked food would be gradual as preferred food was less frequently encountered; and (iii) deer would respond to a lower abundance of preferred foods by eating more of lower-ranked food items at each feeding location. Searching for food alone did not alter diet selection from ad libitum conditions. Deer nearly exhausted their highly preferred food item before switching to lower-ranked ones. Amount of preferred food already eaten during a trial was positively correlated with the time that animals continued searching before switching to lower-ranked food items. Switching was related to amount and type of food encountered and not to amount of food in the pen. Clumping of the preferred food had no significant effect on the amount of food eaten, but did significantly influence types of food encountered by one deer. When preferred food was abundant, it was not always completely eaten the first time a feeding platform was visited. Increases in the intake rates of nonpreferred food items resulted from deer visiting more feeding stations containing nonpreferred food items and not from deer eating more food at each feeding station.