Strangely enough, there are a lot of fan sites about rats.
Rats live in communities, with all the females and children living together until the young males grow up and go off on their own. In small communities, there is usually one male who leads and protects the group of females. He is very territorial, and other male rats either respect or challenge his domain. In a large group, however, "the social system becomes despotic, with one male becoming socially dominant while others become socially subordinate." (Rat Behavior.org)
Social dominance is established through fighting. Here are some ways rats display antagonistic behavior:
- Heedfulness: rats stand motionless staring at each other, may be a challenge.
- Threat displays (these are rare, may occur during heedfulness):
- teeth gnashing
- hair bristling
- back arching
- foot-drumming
- backward earth-throwing with the hind feet
- advance then retreat backwards a few steps
- Attack: swift run toward another rat
- Boxing: rats rear up and push each other with their forepaws
- Jump fight: both rats jump toward each other with their four limbs thrown forward
- Wrestling: rats grasp each other and roll rapidly around on the ground, frequently screaming
- Retreat: withdrawal of loser. Includes:
- flight: loser runs away with no further participation by the winner
- pursuit: winner chases the loser
- escape jump: forward jump by loser to exit from a wrestling ball, or when touched on the rump by the pursuer (Rat Behavior.org)
(RattyRat,com has more information on how rats express Joy, fear, annoyance, anger, dominance, etc.)
Response to Intruders:
"Telle (1966) found that wild rats attack introduced intruders. However, these attacks are not sustained and the intruder is rarely seriously injured because he runs away. Once he reaches the periphery of the colony's territory, pursuit stops, and he is ignored as long as he stays far enough away.
Aggression toward intruders therefore seems to function to exclude intruders from resources like food, shelter, and sexual access to females available to residents, and to chase away surplus animals into adjacent areas." (Rat Bahavior.org)
Rat "Speaking"
Rats often communicate with ultrasonic sounds that humans can't hear. Humans mostly hear them when they are "bruxing" or grinding their teeth, and they do have a vocabulary of "high, abrupt pain squeaks to soft, persistent 'singing' sounds during confrontations." Here is a link to listen to some rat sounds.
BBC Nature talks about how rats have survived by adapting and scavenging.
20 Things You Didn't Know About Rats from Discover Magazine, including how rats can tread water for 3 days and survive being flushed down the toilet.