THERMAL CONSTRAINTS ON USE OF COVER TYPES AND ACTIVITY TIME OF ELK

Use of cover types and activity patterns of radio-collared elk (Cervus elaphus roosevelti) inhabiting the Mount St. Helens blast zone in the State of Washington, U.S.A., were studied under different climatic conditions. Elk use of forest cover during the midday period was not greater (P < 0.12) on clear days than on cloudy days. Estimates of the heat load of a foraging elk indicated that normal body temperatures could be maintained in the seral plant communities of the blast zone despite high radiative heat gain. An increase in wind speeds in mid to late afternoon suggested an increase in convective heat loss. Additionally, elk became inactive and selected bedding sites with little vegetation. Elk compensated for the decrease in diurnal activity time by increasing nocturnal feeding. Abundant, high quality forage in the Mount St. Helens blast zone most likely facilitated these responses to heat stress.