“Behavioral sink” is a term invented by ethologist John B. Calhoun to describe a collapse in behavior which can result from overcrowding. The term and concept derive from a series of over-population experiments Calhoun conducted on Norway rats between 1958 and 1962. In the experiments, Calhoun and his researchers created a series of “rat utopias” – enclosed spaces in which rats were given unlimited access to food and water, enabling unfettered population growth. Calhoun coined the term “behavioral sink” in his February 1, 1962 report in an article titled “Population Density and Social Pathology” in Scientific American on the rat experiment. He would later perform similar experiments on mice, from 1968 to 1972.
In the 1962 study, Calhoun described the behavior as follows:
Many [female rats] were unable to carry pregnancy to full term or to survive delivery of their litters if they did. An even greater number, after successfully giving birth, fell short in their maternal functions. Among the males the behavior disturbances ranged from sexual deviation to cannibalism and from frenetic overactivity to a pathological withdrawal from which individuals would emerge to eat, drink and move about only when other members of the community were asleep. The social organization of the animals showed equal disruption. …
The common source of these disturbances became most dramatically apparent in the populations of our first series of three experiments, in which we observed the development of what we called a behavioral sink. The animals would crowd together in greatest number in one of the four interconnecting pens in which the colony was maintained. As many as 60 of the 80 rats in each experimental population would assemble in one pen during periods of feeding. Individual rats would rarely eat except in the company of other rats. As a result extreme population densities developed in the pen adopted for eating, leaving the others with sparse populations.
… In the experiments in which the behavioral sink developed, infant mortality ran as high as 96 percent among the most disoriented groups in the population.
Calhoun retired from NIMH in 1984, but continued to work on his research results until his death on September 7, 1995.