THE INTERACTION OF FOOD AVAILABILITY AND ENDOGENOUS PHYSIOLOGICAL CYCLES ON THE GRAZING ECOLOGY OF RED DEER HINDS (CERVUS-ELAPHUS)

1. The objective of the study was to establish the role of endogenous circannual physiological cycles in regulating the grazing behaviour of red deer. 2. This was investigated by manipulating the timing of seas onal cycles in red deer hinds by administration of melatonin between J uly and October and comparing the subsequent grazing responses to eith er a low or high herbage biomass at the times of previously observed s easonal decline (autumn) and rise (spring) in voluntary food intake of enhoused animals. Food intake was determined using the n-alkane marke r technique. 3. Melatonin treatment resulted in respective 15- and 10- day advances in the timing of the onset and termination of the breedin g season of non-pregnant hinds, indicating a phase-shift in the underl ying circannual rhythm of reproduction. 4. Melatonin also caused a sig nificant depression in herbage intake by hinds grazing high herbage bi omasses during autumn consistent with an advance in the timing of the seasonal appetite decline. Treatment did not affect the intake of hind s on the low biomasses in the autumn or animals on either pasture duri ng spring. 5. The study demonstrates that endogenous seasonal appetite changes influence level of food intake in grazing deer, but the expre ssion of these seasonal cycles is dependent upon food availability.