Plasticity in avian responses to thermal challenges - An essay in honor of Jacob Marder

Birds show remarkable plasticity in their thermoregulatory responses, often enhancing heat or cold resistance seasonally or in response to experimentally applied thermal challenges. In regions with severe winters these animals commonly undergo substantial winter fattening, elevate their general metabolic level, and increase thermogenic capacity and endurance. Indications also exist that some species, at least, also increase their capacity for mobilizing energy substrates during cold challenges. Some of these responses also are induced by cold conditioning in the laboratory. The onset of warmer seasons or exposure to higher laboratory temperatures can lead to downregulation of general metabolic level, thereby reducing the thermal load with which birds must contend during the heat of summer days. However, the most spectacular phenotypic adjustment to heat thus far documented is that evident in the heat-acclimated rock pigeon (Columba livia), which achieves a remarkable resistance to high ambient temperatures through expression of a highly efficient system of cutaneous evaporation for cooling. Professor Jacob Marder played a major role in the characterization of this response and in the analysis of its functional basis. It is appropriate to dedicate this essay to his memory in recognition of his important contributions to a fuller characterization of avian thermoregulatory plasticity.