Thermoregulatory Role of the Unfeathered Head and Neck in Male Wild Turkeys

Abstract

ABsTmAcr.-The brightly colored, unfeathered heads and necks of male Wild Turkeys (Meleagris gallopavo) are generally thought to function in sexual selection. However, studies in other bird species have suggested that uninsulated body regions may serve an important role in heat dissipation. I test the heat-dissipation hypothesis in Wild Turkeys by experimentally reinsulating the heads and necks of Wild Turkeys as though they were feathered. The oxygen consumption, thermal conductance, cooling capacity, surface temperatures, and core temperature of control and reinsulated Wild Turkeys were compared at 00, 220 and 35?C. Head insulation resulted in significantly increased rates of oxygen consumption, higher body temperatures, and decreased cooling capacities at 35?C, but had no significant effect at the other temperatures tested. It appears that behavioral changes at low temperatures, such as tucking the head under the back feathers, effectively prevent the heat loss that would otherwise be caused by the absence of feathers. However, if the head were feathered, turkeys at high temperatures would be unable to dissipate sufficient heat to maintain thermeostasis. Thus, given this finding for Wild Turkeys, it can no longer be said that in all cases bare heads in birds have evolved by sexual selection alone. Loss of head and neck feathering in Wild Turkeys and other birds may have allowed these species to take advantage of regions in time and space that previously were unexploitable due to the dangers of hyperthermia. Received 22 June 1994, accepted 27 January 1995.