Behavioral Response of Mule Deer to a Highway Underpass

A concrete box underpass 3.05 x 3.05 m (10 feet) and 30.48 m (100 feet) long under Inter-state 70 in west central Colorado was monitored for deer use during 4 years following its completion in early 1970. A seasonal mean of 345.1 +- 133.0 (SD) mule deer (Odocoileus hemionus) passed through the structure when moving to or from their summer range. A video time-lapse surveillance system recorded behavioral responses during four migration periods, spring-summer and fall in 1972 and 1973. On the basis of video tape playback of 4,450 approaches and 1,739 entrances, deer displayed 3 basic overt responses: look-up, tail-up, and muzzle-to-ground. The frequency of the look-up response was indicative of the reluctance of the animals to go through a structure of this size and character. The underpass was successful in permitting about 61 percent of the local deer population to migrate safely under the highway.