Circannual rhythm of torpor and molt in the ground squirrel, Spermophilus beecheyi.

Using cool, white, fluorescent lamps photoperiods mimicking those in Santa Barbara, CA, entrain circannual rhythms of mass and torpor of Spermophilus beecheyi so that maxima occur about September for 6 years. Cycles with 12-hr photofractions or continuous light has short circannual periods of mass and torpor. After a phase-shift of 6 months, some squirrels entrained in about 3 years. Squirrels kept 6 months on 10-hr and 6 months on 14-hr photofraction had weakly entrained circannual mass and molting rhythms. In entrained females start of torpidity advanced each year. Torpor appears rarely in males or in females with access to running wheels.