Aspects of circulatory physiology of montane and lowland birds

Abstract

Abstract o 1. Weights of body, heart, and lungs, tarsometatarsal lengths, and several hematological parameters (red blood cell count, hemoglobin concentration, and hematocrit) were measured in closely related birds at four montane and lowland locations. 2. Lung and heart weights of highland birds average 37 and 11% higher, respectively, than those of lowland individuals of similar size. Average hematological parameters are 23% (red blood cell count), 17% (hemoglobin concentration), and 7% (hematocrit) higher in the former animals than in the latter. 3. Pine siskins (Spinus pinus) captured in midwinter in Michigan are the only birds that have significantly elevated blood properties over those of their montane relatives. A comparison of blood values of American goldfinches (S. tristis) during summer and winter in Michigan reveals an increase in blood characteristics of winter individuals similar in extent to that of winter pine siskins. This raises the possibility that the blood parameters of high altitude birds reflect adjustments in oxygen carrying capacity to meet the thermogenic demands as well as hypoxia characterizing cold montane habitats. 4. Birds that migrate seasonally between high and low altitude do not differ in any of the morphological or vascular characteristics analyzed from those of individuals residing continuously in the mountains. 5. Since the physiological characteristics of montane birds probably reflect responses to multiple demands of the physical environment, identification of the responses specific to hypoxia associated with the altitudes at which these birds live will require further study.