Physiological Responses of the Blue-Throated and Rivoli's Hummingbirds

Abstract

A variety of physiological responses were studied in the 2 largest species of hummingbirds found in the United States. Levels of standard metabolism are similar to those predicted by the weight-metabolism relationships of larger birds. Minimal homeothermic heart rates of 7-8 beats/sec were recorded, while maximal recorded levels were 20-21/sec for both species. Torpidity heart rates were considerably lower. Evaporative water loss ranged from 6.7 to 12.5 mg H2O/g/hr at 15[degree] and 34.8[degree]C, respectively for homeothermic birds, and decreased markedly during torpor. Wing beat frequencies are inversely related to the length of the wings. Rates of entry into and arousal from torpor are inversely related to the body weight of the birds.