Nocturnal Hypothermia and Oxygen Consumption in Manakins

Red-capped Manakins (Pipra mentalis) and Golden-collared Manakins (Manacus vitellinus), two species of small, frugivorous, tropical passerines, showed facultative hypothermia and reduced oxygen consumption at night. The lowest body temperature measured in M. vitellinus (30.5°C, when the ambient temperature was 19.5°C) represents a reduction of more than 40% in the difference between body temperature and ambient temperature. Under these circumstances, a reduction of more than 40% in the rate of oxygen consumption would also occur during the period of regulated hypothermia. Even moderate hypothermia at ambient temperatures typical of the lowland tropics substantially reduces the energy expenditure of a resting bird.