Under dim (35-55 lux) constant light conditions, 88.9% of mutant flies show robust locomotor activity rhythmicity, with an average period length of 24.0 hours (depending on the lines used), whereas control animals are largely arrhythmic under these conditions.

cry^OUT mutants subjected to light-dark (LD) (with twilight simulation) and temperature cycles, in phase, display tiny morning peaks and sharp evening peaks of activity. They are completely inactive in the dark phase. After a shift of the LD cycle, cry^OUT flies seem to very slowly re-entrain to the LD cycle, with darkness exerting a strong negative masking effect on the activity so that the trajectory of the rhythm is disrupted during the dark phase. Mutant flies take longer to re-synchronize compared to wild-type flies and either seem to free-run (in LD) or to retrain to temperature cycles when in natural light-moonlight cycles (which reduces the negative masking effect of darkness). After a shift of daylight-moonlight (LM) cycles, the evening peak of cry^OUT mutants remains at the same phase as before the shift (whereas wild-type follow the shift). cry^OUT mutants are mainly entrained by temperature cycles and are neither free-running nor entrained by light-moonlight cycles.

Homozygous cry^OUT mutants show short circadian free-running periods under blue light. After experimental exposure to a 300 microT magnetic field, the majority of the cry^OUT mutants do not show any period changes, or if changes occur, the changes are significantly smaller than those in wild-type flies.

cry^OUT mutant flies show anomalous rhythmic locomotor activity under constant light conditions (wild-type flies are arrhythmic under these conditions).