Heart Size and Altitude in Ptarmigan

Abstract

Relative heart weight is known to increase with altitude in several bird species (Hartman, Condor 57: 221, 1955; Norris and Williamson, Wilson Bull. 67:78, 1955; Dunson, Condor 67:215, 1965). The effect of altitude on heart size in birds was first illustrated by Strohl (Compt. Rend. Acad. Sci. Paris 150:1257, 1910) who compared Rock Ptarmigan (Lagopus mutus) from 2000 to 3000 meters elevation with Willow Ptarmigan (Lagopus lagopus) from 600 meters, but these data have since been discounted as being the result of interspecific differences (Stieve 1934, in Hartman, Smithsonian Misc. Publ. 143:1, 1961). Johnston (Wilson Bull. 75:435, 1963) and Stieve (loc. cit.) found similar heart-size differences between these species when captured at the same elevation. Selection, however, might still be expected to favor a larger relative heart size in the species whose range has a higher elevation on the average, and, therefore, these heart-size differences may still reflect adaptations to altitude. A third species, the White-tailed Ptarmigan (Lagopus leucurus), occurs at still higher average elevations than the ptarmigan previously studied. It was felt that information from this species might clarify this relationship. Heart-to-body weight ratios were obtained from 18 White-tailed Ptarmigan that died during a temperature-regulation study. The birds had been captured on Logan Pass (2100-2300 meters) in Glacier National Park, Montana, in June through August 1965. SHORT COMMUNICATIONS 185