-Metabolic rates and body temperatures of four captive Anhingas (Anhingu anhinga) were measured over a range of ambient temperatures. In addition, Anhingas were observed in the field in an attempt to correlate the frequency of behaviors, such as wing-spreading, with environmental conditions, such as the intensity of solar radiation and ambient temperature. Anhingas have low basal metabolic rates and high thermal conductances for their mass. The frequency of spread-winged behavior increases at higher solar intensities and is inversely correlated with ambient temperature. Anhingas assuming spread-winged postures orient with their backs to the sun, maximizing the surface area exposed to insolation and maintaining an angle of incidence of approximately 90”. In contrast, birds engaged in gular flutter face into the sun, thereby minimizing the surface area exposed to insolation and increasing the angle of incidence. Anhingas spread their wings to dry the plumage and to absorb solar energy during cool weather. They thereby supplement their low metabolic rates, compensate for their high thermal conductances, and replace heat lost via evaporation and convection due to wetting of the plumage. _ Although spread-winged behavior is well known in darters, its function is not established (Clark 1969, Kennedy 1969). Suggested functions include the synthesis of vitamin D (Kennedy 1968, 1969); the removal of ectoparasites (Kennedy 1969); skin conditioning during molt (Potter and Hauser 1974); feather maintenance (Kahl 197 1); wing-drying (Rijke 1968, Siegfried et al. 1975, Berry 1976); and thermoregulation (Heath 1962, Clark 1969, Kennedy 1969). The wing-drying hypothesis is especially attractive because Casler (1973) and Rijke (1968) found that these birds possess wettable plumage, which allows water to penetrate the air spaces next to the skin. This reduces their buoyancy and facilitates underwater stalking of prey. I examined the metabolism of Anhingas (Anhingu anhingu) in the laboratory, and their behavior in the field, to determine if the birds use spread-winged behavior in drying the wings or in thermoregulation.