These animals are within a similar size range of 2 to 4 grams. They all feed on nectar while hovering in front of flowers. Heterothermy also occurs commonly in small bats and in several families of rodents. When aroused and active, heterotherms have the advantages of thermoregulating animals such as substantial physiological independence from environmental temperature. But when inactive, these animals share the frugal patterns of energy expenditure characteristic of poikilotherms.
Large animals are probably too big to be heterotherms due to the effects of thermal inertia.