Basking Behavior of the Hawaiian Green Turtle (Chelonia mydas)l

Observations were made on green turtles basking on the white sand beaches at French Frigate Shoals in the northwestern Hawaiian Islands. The highest rectal temperature recorded from the basking turtles was 31.3°C, but the surface temperature of the carapace attained values as great as 42.8°C. During basking, the turtles flipped sand onto their carapaces, but they did not appear to orientate their position in relation to the sun. The duration of basking was inversely related to the mean temperature of a black globe, and the basking beaches were relatively cool. The pattern of breathing during basking consisted of periods of breath-holding alternating with single breaths. The amount of time that the turtles basked varied from 0.3 to 7.5 percent of the total time they were under observation. The biological significance of basking and the advantages that might accrue to Hawaiian green turtles from their unique basking behavior are discussed. in a tank at the Hawaii Institute of Marine Biology basked when given the opportunity, although turtles of this age have not been observed to bask under natural conditions. At French Frigate Shoals the incidence of basking was highest during the breeding season, when, presumably, the number of turtles present was greatest. Balazs (1980) showed further that during the nesting season, the number of basking turtles declined as the egglaying season progressed. However, there is not a month in the year when turtles have not been observed to bask. Both male and female turtles have been reported to bask (Balazs 1980). Turtles that formerly basked off the coast of Mexico and in the Galapagos Islands were predominantly female (Fritts 1981) and so also are the turtles that presently bask in Australia (Bustard 1973). In another report, Balazs (1977) described the nocturnal basking behavior of green turtles at Necker Island in the northwestern Hawaiian Islands. This latter behavior points to the possibility that the function of basking may not be that of acquiring heat by solar radiation, although this is believed to be one of the principal functions of basking in freshwater turtles (Boyer 1965). 129 TERRESTRIAL BASKING IS COMMON in freshwater aquatic turtles, and its biology has been described by several authors (Boyer 1965, Moll and Legler 1971, Terpin, Spotila, and Foley 1979). Among sea turtles, however, basking on land is comparatively rare. Only the green turtle (Chelonia mydas) has been reported to bask, and it does so only in certain parts of the world, notably in the northwestern Hawaiian Islands. One of eight breeding colonies that have been designated for high priority by the World Conference on Sea Turtle Conservation (1979) is located at French Frigate Shoals in the northwestern Hawaiian Islands. Little is known about the basking behavior of Hawaiian green turtles. Balazs and Ross (1974) showed that 6-month-old turtles kept 1 This study was supported by a grant from the National Geographic Society. Manuscript accepted 21 January 1982. . 2 University of Hawaii, John A. Burns School of Medicine, Department of Physiology, and Pacific Biomedical Research Center, Kewalo Marine Laboratory, Honolulu, Hawaii 96822. 3 University of Hawaii, Hawaii Institute of Marine Biology, Kaneohe, Hawaii 96744.