Meeting Abstract

48.6  Jan. 6  Triple partitioning of total evaporation reveals the cloaca as a site of thermoregulatorily important rates of evaporative cooling in Inca doves, Columbina inca HOFFMAN, T.C.M.**; WALSBERG, G.E.; DENARDO, D.F.; Arizona State University; Arizona State University; Arizona State University ty@asu.edu

Because of the high latent heat of vaporization of water, evaporation is an important thermoregulatory mechanism in animals from diverse taxa. Among endotherms, evaporative cooling allows for thermostasis even under conditions in which an animal gains heat conductively, convectively, radiatively, and metabolically. Historically, avian evaporation has been studied from the standpoint that there are two primary routes of evaporation: the buccopharyngeal epithelia and the skin. This paradigm has ignored one of a bird’s two primary orifices, the cloaca, as a potential site of thermoregulatory evaporation. Because columbiforms are superlative among avian species in their ability to tolerate extremely high ambient temperatures in nature, we measured rates of evaporation in Inca doves, partitioning total evaporation into its buccopharyngeal, cutaneous, and cloacal components at each of four temperatures. Buccopharyngeal evaporation and cutaneous evaporation increased throughout the range of air temperatures studied. At 30�, 35�, and 40�C, cloacal evaporation was negligible. However, at 42�C, the rate of evaporation from the cloaca nearly equaled that from the panting bird’s mouth, indicating that cloacal evaporation can be important for thermoregulation and that it can be controlled. This suggests that some birds can respond to the conflicting demands for hydrostasis and thermostasis by conserving cloacal water at lower temperatures and evaporating cloacal water when other modes of heat-loss, including evaporation elsewhere, no longer suffice.