A PREDICTABLE PATTERN OF DAILY ACTIVITY BY THE POCKET GOPHER GEOMYS BURSARIUS

Because subterranean mammals live in a microhabitat buffered from envi ronmental extremes, it is often assumed that their daily activity patt erns are weakly structured at best. The daily activity (time outside t he nest) of a natural population of plains pocket gophers, Geomys burs arius, was examined using radiotelemetry. A bimodal pattern of activit y was observed in which gophers were most likely to be active at night (2200-0600 hours) and in early afternoon (1300-1700 hours). Total dai ly activity averaged 400 min/day. Activity-bout length varied with tim e of day. Morning bouts were the shortest, afternoon bouts the longest , and bouts at night were of intermediate length. The overall pattern of activity was best explained as a mechanism for avoiding burrow temp erature extremes. Gophers would have conserved energy by remaining in their nests in the morning when the burrows were coolest, and may have reduced the risk of hyperthermia by avoiding activity in the late aft ernoon when burrows were warmest. Because an endogenously controlled c ircadian metabolic rhythm has never been demonstrated in pocket gopher s, the observed pattern of activity was probably environmentally induc ed. The results suggest that the subterranean microhabitat may require efficient use of both time and energy by its mammalian inhabitants.