Record Details

Bartholomew, George A
A field study of temperature relations in the Galapagos marine iguana
Journal Article
Amblyrhynchus cristatus
When marine iguanas are on shore, their preferred body temperature lies between 35 and 37° C, and this is 10° C (or more depending on the season) above the body temperature at which they operate while feeding at sea. They appear to be behaviorally normal with body temperatures as high as 40° C and as low as 25° C. Marine iguanas spend most of their time on shore. At Punta Espinosa on Isla Fernandina where the largest known population of the species occurs, thousands of animals haul out on the bare lava flows and remain exposed to the intense radiation of the equatorial sun throughout the day. Black bulb temperatures may exceed 50° C, but these lizards, without resorting to shade, are able to keep their body temperatures below 40° C by making postural adjustments which minimize the area of body surface exposed to the sun, and allow a maximum exposure to the relatively cool trade winds. If marine iguanas are tethered so that they cannot employ this postural thermoregulation, they soon overheat and die when exposed to the full sun. The reluctance of marine iguanas to escape into the sea when disturbed, which has been so often commented on since the time of Darwin, appears to be related to a reluctance to cool off rather than to an avoidance of the sea. The cooling rates in water and the heating rates in air of marine iguanas are inversely related to body size. The relatively slow rate of cooling in water suggests the existence of cardiovascular adjustments for reducing heat loss when in the water.