Rat Food

Rats with access to shelter and to food eat at fairly regular intervals. White rats with access to food at a short distance from their nest have a cycle of three to four hours, and feeding coincides with the later part of a period of maximum general activity. Le Magnene and Tallon have described such cycle, but observed a good deal of individual variation in the feeding rhythms of albino rats. This is a common feature of the performance of animals in experiments on behavior. It is a source of difficult for experimenters, which is perhaps why its existence is often ignored or glossed over. Nevertheless, some rats display a fairly consistent circadian (twenty-four-hour) rhythm; the modal interval between meals is about 140 minutes, and the amount eaten at each meal, 2 to 3 g. Meals taken during the night are larger than those eaten in daytime: hence nocturnal consumption is about 50 percent higher than that during daylight.

The greater consumption of food during darkness had already been observed in other researchers, reviewed by Bolles. Circadian rhythms are usually recorded in laboratories in which there are unchanging periods of dark and light, each of twelve hours. Condition are similar near the equator, but not elsewhere; and in no major environment are the night always wholly dark.

In the natural environment, like the rat that living in the jungle, in observation, the rats fed almost wholly at night. This was probably not a consequence of some autonomous rhythm, but was imposed by the cycle of light and darkness and by the absence of disturbance by man at night. By making food available at a particular time.