All rat species may attack if they feel threatened, or are provoked or scared and need to fight their way out of a confrontation.
If your rats are fighting with one another and there's danger of blood being shed— which often results in significant injuries—immediately isolate the aggressive rat.
Dominance Relationship
Fighting between cage-mates is rare but can be recognized when one rat hides from the other, if one rat injures another, or if the attacking rat has raised fur. Rats are social animals and enjoy living with other rats; they can become depressed if they are alone.
As with any social animals kept in groups a certain level of fighting is necessary to establish and maintain the hierarchy when adults or for play in kittens. This varies a lot with rat age and sex and also from group to group.
It's easy to tell when your rats are playing. They're having a great time, bouncing around, no puffed-up fur, no biting, no blood is drawn.
Play fighting in the rat involves attack and defense of the nape of the neck, which if contacted, is gently nuzzled with the snout. Because the movements of one animal are countered by the actions of its partner, play fighting is a complex, dynamic interaction.
Larger rats would invariably beat smaller rats most of the time, given their 'pinning' game was very body weight dependent. But when larger rats would not let smaller rats win once in a while (Panksepp estimated around 30% of the time), the smaller rats would stop playing with them.
Rats are highly social animals, and mainly communicate with one another in two ways: through ultrasonic vocalizations and pheromones. Most research on pheromones has been dedicated those regarding sexual behavior, but more recently pheromones which signal danger to conspecifics have been identified in rodents.
Summary: Rats show altruistic behavior and avoid harming other rats.
Rats are social animals with clear social structures. They learn from one another. If a rat eats something and drops dead, the other rats who witness it will avoid it. In the same way, if they see a rat caught in a trap, they will become much more cautious.
Rats exhibit aggressive behavior when threatened. They may fight, chase, bite and box. Rats also display some behaviors such as sidling and belly-up defensive postures.
Having pets makes no difference. Rats are not deterred by cats or dogs.”
Rats are incredibly hardy animals who have never shown any problem adjusting to change. Usually that change is the introduction of a new poison, as humans constantly work harder and harder to exterminate these animals. But perhaps no other animal resists such attempts better than the rat.
Rats cannot tolerate smells such as ammonia, mothballs, peppermint oil, crushed cayenne pepper, and pepper spray due to their intensified sense of smell. Clean and uncluttered homes and yards scare rats due to the lack of food and places to hide, as well.
Continue to observe their behavior over the next several days to determine the cause and whether there could be a recurrence. If, however, one of your rats was seriously hurt during the fight, cage them separately until you know for sure the rats can be housed together safely.
Typically, a single nest will have five to 10 rats living in it, although this may be lower for a very recently established nest or a little higher after a litter is born. Furthermore, rats sometimes establish multiple nests close together forming a colony.
They also have an acute sense of hearing, frequently using ultrasound to communicate, which is especially sensitive to any sudden noise. Rats are social animals, so if you see one rat then there are likely to be more nearby.
It takes four or five days for a rat to die of starvation, but if they can't find any food at all, they will usually move on to a new spot before they die. The more active they are, the faster they will dehydrate and deplete their energy reserves, so the less food available, the less active they will be.
Rats and mice are nocturnal with most activity taking place between approximately one half hour after sunset to about one half hour before sunrise. Garbage is an excellent food source for rodents.
Previous research has shown the much-maligned rodents assist comrades in need, as well as remember individual rats that have helped them—and return the favor. Now, a new study builds on this evidence of empathy, revealing that domestic rats will avoid harming other rats.
A “rat king” is a group of rats whose tails are intertwined and stuck together. Sometimes the tail hairs are simply entangled, and at other times sticky substances like sap or gum may be the culprits. As many as 32 rats have been found joined together in this way.