Today in Sweden there is talk about extremely aggressive rats being common among the pet/fancy rats. But how do you know what is the normal amount of aggressivity in the rat? Well, you study how wild rats of the same species (the brown rat, Rattus norwegicus) behaves. Through the years many scientist have been studying wild rats.
In the wild the brown rat lives in big packs (colonies), with lots of males and females together. Some of these rat packs may contain several hundred rats. All rats in the same pack lives in harmony with eachother, they never fight among themselves.
One interesting result in common of the scientist's studies is that only adult male rats are territorial and they attack only adult strange male rats that intrude in their territory. The territorial (resident) males ignores both adult strange females and strange young rats (all rats under 4 moths of age). Seldom a male rat have been seen attacking a strange adult female, but usually they are tolerated.
The territorial behaviour in the wild brown rat is typically seen as the resident males chases away any strange adult male (over 4 months of age) that enters the territory. This is mainly done by aggressive threat signals, their raise their hair on end and so on to scare the stranger away. Seldom they actuallty attack. But if an attack occurs the wild rat uses his front feet as attack weapons, not his teeth. The damage from the attack is seldom serious, but shows the intruder that the resident male really want him to leave. One interesting detail is that the intruder never attacks, only the resident male/s. During the attack the resident male use his teeth as to small bites in the extremities, often with no other injuries than some fur loss as a result.
Wild brown female rats are not territorial. They only defend their nest if they have young. Some females defend their young against all rats except all her fellow pack members, without hesitation letting any rat belonging to her pack come freely to her nest. Even big males of her own pack can come into the nest and greet the newborn babies. Some females defend their nest and young againt all rats period.
Hierarky in the wild rat pack is determined mainly by size and age. This species does normally not fight for status.
But if a human collect several grown males from different packs and put these together there may be a lot of fights. These fights may be started in order to keep territory rather than to accieve a higher status, since these males do not know eachother. Strangely enough this experiment that shows forced unnatural behaviour in the brown rat, is the most quoted. The result if the fights in this experiment is that the males can be divided into Alpha, Beta and Gamma males. The Alphas can only be beaten in a fight by another Alpha. The Betas can be beaten by Alphas. The Gammas can be beaten by any of the males and has to flee or die (during this experiment). It seems like some scientists actually enjoyed inducing rat fights among their animals. Sadly enough this experiment has given raise to many mis-conceptions about the behaviour of rats.
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In terms of pet/fancy rats this means that any rat that attacks any cage mate, any female or any young rat in an established group is showing unnatural behaviour.
Females are not territorial, and shall never fight among themselves. Females defend their young. Some females even defend their young against their owner, that is natural behaviour.
Written by Eva Johansson.
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Copyright Eva Johansson.
Last update: 11th of August 2006.