Modification of Body Temperature by Activity in Brazilian Hummingbirds

Abstract

Hummingbirds, together with certain shrews and bats, represent the smallest homeo-thermic animals. They have a correspondingly large thermal conductance and therefore face a more difficult task of thermoregulation than larger animals. Observations on the level and variation of their body temperature and of their energy balance are conse-quently of much interest. Hummingbirds are, moreover, one of the few groups of birds in which lowered body temperature has been observed. Pearson has described torpor in both a Californian species, Calypte anna (1950 and 1954) and an Andean species, Oreotrochdus estella (1953). Bartholomew, Howell and Cade (1957) have also de-scribed torpor in the Anna Hummingbird. Ruschi (1949), in his extensive report on the Brazilian Trochilidae, listed temperatures for nine different species with after-noon values ranging from 39.5 " to 44.6' C. and night values (sleep) ranging from 36.6 " to 40.5' C. He also observed torpor in' all these species at body temperatures ranging from 32.0' to 36.6' C. The present study extends our knowledge of body temperatures in hummingbirds as represented by three Brazilian species with em-phasis on the daily cycle and the influence of various types of activity. ACKNOWLEDGMENTS