Failure of temperature to entrain a circannual rhythm of mass in California ground squirrels (Spermophilus beecheyi)

Abstract

To determine what environmental factor is the Zeitgeber for the annual change in mass, California ground squirrels (Spermophilus beecheyi) were exposed to several regimes of temperature and length of day. The squirrels were captured when age 4–5 months, kept individually in cages with excess food and nesting material. The temperature was varied with a 6‐month phase shift (SH). The length of day was the same as Santa Barbara (SB) or 6‐month phase shift (SH). The light was provided by cool white bulbs at 10–600 lux.

The first experiment consisted of keeping squirrels at either SB or SH length of day and at constant temperature (20°) for three years and then changing to SH temperature for 3 years. None entrained although at age 6, 2 might be entrained. The second experiment repeated the first except that the SH temperature started at age zero. None has entrained by age 5. None of a third group, placed at SH temperature and SB length of day, has entrained by age 3. The conclusion is that these regimes of temperature and length of day, which resemble natural conditions, do not entrain the annual change of mass.