Nocturnal variation in body temperature of Griffon Vultures

The variation in body temperature over 24 hr was measured by implanting temperature measuring radio transmitters in the abdominal cavity of six captive Griffon Vultures (Gyps fulvus). Body temperature was measured when the birds were under three different feeding regimes: within 24 hr of feeding (while digesting), 2-3 days after feeding (post-absorptive state), and 9.5-10.5 days after feeding (food deprived). For all birds, nocturnal body temperature was significantly lower than diurnal body temperature. The decline in body temperature at night was significantly greater in food deprived birds, which at 10.5 days post-feeding had dropped by 4-6 degrees C. We suggest that this is an adaptation to reduce energy requirements of Griffon Vultures during periods of food shortage.