Abstract: Nearly all organisms mirror environmental cycles in their rhythmic behavioral output.  Endogenous circadian timing systems presumably enhance the chances of survival by preparing an organism for forthcoming events.  As part of a long-term study of the ecological adaptiveness of the SCN, wild-caught chipmunks were assigned to an SCN-lesioned group or one of two control groups.  All study animals were radiocollared, and survival was monitored with radio telemetric tracking during daylight hours.  An automated data logging system was a noninvasive measure of activity patterns within the burrow, and a 26-hour census provided an actual count of active animals above ground.  To aid in the interpretation of behavioral data, chipmunk burrow systems were excavated.  Nightly radio telemetric tracking near the den was used to measure burrow shifts.  Many of the SCN-lesioned chipmunks survived for the two months of measurement in the field.  No chipmunks were found above ground at night, although some nighttime restlessness was observed in SCN-lesioned chipmunks.  Most of the chipmunks in the study maintained the same burrow system for the two months of study.  No immediately obvious differences were found in the behavior of SCN-lesioned and control chipmunks.  Instead, the SCN may have subtle effects that are exhibited over an individual's life-span or over many generations.