The Role of Behavior in the Temperature Regulation of the Masked Booby

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Abstract
The temperature regulation of masked boobies (Sula dactylatra) was studied on Isla Espanola in the Galapagos Archipelago. Body temperatures of adults averaged 40.7[degree]C during midday and 38.3[degree]C after dark. Temperature regulation of adults under conditions of heat stress involved a number of behavior adjustments; orientation with back to sun, elevation of the scapulars and drooping of the wings, sustained gular flutter. Brooded chicks and incubated pipped eggs had temperatures between 38[degree]C and 40[degree]C. When placed in the open shade hatchlings cooled rapidly and the rate of diminution of body temperature was inversely related to body weight. By the time the chicks weigh about 400 g and are covered by down they can maintain a high and uniform body temperature. The amount of visible shivering in chicks increased directly with size. Ability to regulate body temperature in chicks placed directly in the sun increased with size. The body temperatures of hatchlings approached lethal limits within 20 min. of exposure to full sun. Downy chicks weighing near 400 g were able to stabilize body temperature near 42[degree]C. Chicks of all sizes employ gular flutter when exposed to heat stress. Young chicks are dependent on brooding by the adults for protection from the thermal conditions of both heat and coolness.