Mice live inside a nest, and it won’t just be one or two mice in there; there’ll be a load of them. One nest can be home to one male with his string of females, all of which he’ll mate with, and he’ll be very territorial about that nest, too. He won’t permit any other male to come inside his space and potentially mate with his females, fighting off any that dare to do just that. For the most part, however, males are pretty respectful. It would be unusual for a male to walk into the habitat of another looking for a fight. The only time that males do get along when in the same habitat is if they are related — siblings, usually — or if they have been kept together from a very early point.

Nests are almost always very close to a source of food, and will be created from soft materials. When a mouse chews through a cardboard box, for example, to get to the cereal inside, they’ll use the chewed-up cardboard as material to build a nest. They will also chew through soft furnishings for nesting material, paperwork, clothing, plastics, and more.

When a lot of food is NOT available, females are known to fight each other for the rights to that food. They will also fight to ensure that other females do not kill and eat their young. Territories are also known to be larger with less food, and aggressive behavior, on the whole, is increased. When there is abundance of food, the entire group gets on better with each other, and the sizes of each group’s habitat or territory decreases. In urban spaces, lots of human waste is on offer, which is food for these rodents. Because there is a lot of food available, more mouse groups can live in a smaller area, such as multiple groups of mice within a single home or building.

Mice that live in urban (human) areas are known for coming together, with females even nursing and caring for each other’s young. Related mice won’t usually breed with each other, but two groups that aren’t related will come together to form breeding groups, especially when numbers are culled.