Activity cycles of the rhesus monkey(Macaca mulatta)under several experimental conditions, both in isolation and in a group situation∗∗∗

The circadian temperature rhythm in Syrian hamsters as a function of the number of animals per cage

“…This fits with the observations on monkeys as they were found more active when they were in groups (Yellin and Hauty, 1971), and it fits as well with our observations on the circadian temperature rhythm in Syrian hamsters.…”

The Nocturnal Behavior of Caged Rhesus Monkeys (Macaca mulatta )

“…The present study was conducted in a screened porch-like enclo sure that allowed the gradual shift from light to dark at dusk and dawn rather than the abrupt shifts used in the Yellin and Hauty [1971] study. The present study was conducted in a laboratory setting and no direct attempt was made to duplicate a natural setting.…”

“…Furthermore, the observed pattern of activity was highly stable and the photoperiodic dependency was common to all experimental conditions. Yellin and Hauty [1971] found that an artificially controlled light/dark cycle yielded an average circadian period of activity of 24 h under several experimental conditions. In one of the few studies that included compari sons of nocturnal behavior, they divided the 24-hour time period into 3-hour segments and found a significant difference between day (light) 12 h and night (dark) 12 h. There was not a significant difference between any of the dark periods, although occasional bursts of activity occurred during the dark period.…”

Influence of Sociality following Isolation on Feeding Rhythms of Monkeys Entrained to Artificial Light Schedules

“…Although eating from dusk to dawn is rarely seen in free-ranging monkeys [Altman, 1962;Vessey, 1973], it is not uncommon in captive animals. 1 monkey, in the study by Yellin and Hauty [1971], ate only during dark hours. Numerous other reports on the behavior of captive' animals [i.e., Hamilton, 1972;Van Hoof, 1967] have shown that there need not be a relationship between the eating habits or feeding schedules of captive animals and free-ranging animals.…”

“…He urged that the social environment be added to light and temperature as a factor able to entrain circadian rhythms. Results from subsequent studies, [i.e., Aschoff et al, 1971;Yellin and Hauty, 1971] further established the social factor's ability to control the circadian rhythms of primates.…”