Some males were frequent recipients of violence that they had to endure because there was no escape.

Some males still tried to mate even if that caused them to suffer violence from stronger males.

Those who survived were often unprepared to care for their own offspring once they had them.

Of those that did breed, strange behaviors started to show, like violently attacking the infants (this is not uncommon for some reason, rodents sometimes eat their offspring) or stopping caring for the offspring long before it was normal.

Some females made groups and created their own territories living together and violently rejecting any male approaching, with no apparent interest in breeding.Interestingly, the dominant males allowed some males to remain, although these males exhibited odd behavior, as rather than try to mate with the females, the males would attempt to mate with the dominant male, and the dominant male would let them. Some dominant males made harems, taking control over several female rats to mate with them.Some of the behaviors observed included:

With time, the rats started to show bizarre conducts. The case was divided in four interconnected rooms able to hold a dozen rats each. As the rats were provided with food, water, nesting materials and protection from predators it was called 'Utopia'. The first experiments were made between 19 using 32 to 56 Norwegian rats in a 10×14-foot case in a barn.

Rat utopia stephan moulex