Effects of hunger and tannic acid on food intake and foraging behavior in Microtus fortis

The influence of hunger and plant secondary compounds on food selection and foraging behavior in Microtus fortis were measured in this study. The three selected kinds of tannic acid food were measured with the cafeteria method. The voles were first offered with food ad libitum for a period of 4 days. Food intake was recorded daily for calculation of average food intake by each vole. The calculated average food intake was multiplied by a hunger index (0, 25, 50, 75 or 100). Measurements were made over 4 consecutive nights for 2–4 feeding bouts per animal per night. The results indicated that hunger increased food intake, but had no significant effects on food selection. 0% tannic acid food was the most preferred food, and the intake of 6% tannic acid food was the least. Ingestion rate and bite size of voles increased with severity of hunger, but the feeding frequency was not significantly affected by hunger, and the time of feeding bout increased slowly. When the amount of food that voles have been offered is 25% more than that when they freely access to the food, the time of the feeding bout of hungry voles was significantly increased. These results suggested that voles increased their food intake mainly by increasing bite size when they were in hunger. The changes in foraging behavior indicated that herbivores increased their bite sizes and food intake rate to satisfy their nutritional demands rather than prolonged their foraging time and decreased the time for defending or reproductive activities to increase the amount of food intake.