Here's why:
* Competition: Mice and rats compete for the same resources, like food, water, and shelter. This creates tension and can lead to aggression.
* Territorial: Both species are territorial, and they will defend their space against rivals, including members of the same species.
* Predatory instincts: While not always the case, larger rats may sometimes view mice as prey.
However, there are some exceptions:
* In captivity: When raised together in controlled environments, mice and rats can sometimes coexist peacefully. However, this is not guaranteed, and careful monitoring is necessary to prevent aggression.
* Rare instances: There are rare cases where mice and rats may tolerate each other in the wild, but this is more likely to occur when resources are abundant and there's less competition.
In general, it's best to assume that mice and rats will not get along and to keep them separated.