Decoursey and Krulas (1988)

• • The sample consisted of 30 chipmunks with SCN (suprachiasmatic nucleus-targeted) lesions, 24 surgical controls (a controlled surgical procedure to mimic the damage) and 20 intact controls.
• •After functionally removing the SCN in 30 chipmunks and returning them to their natural habitat, it was observed that after 80 days significantly more of those chipmunks had not survived in comparison to a control group with normal functioning SCNs.
•  Mortality during the first 14 days was 50% for the SCN-lesioned animals and 37.5% for surgical controls while none of the intact controls were killed
•  Therefore, this suggests that having a biological rhythm such as the sleep/wake cycle does indeed aid survival (the chipmunks were likely to have stayed awake in their burrows at night and therefore be under more danger of predation due to the noise created)