When housing male mice (bucks), what behavioral outcome frequently results if they are kept together unneutered after reaching sexual maturity?

They become territorial and aggressive, frequently leading to serious fighting.

The social dynamics within mouse groups differ significantly based on sex and reproductive status. While female mice (does) generally coexist peacefully, especially in same-sex groupings, this pattern does not hold true for adult males. Once male mice (bucks) reach sexual maturity, territorial instincts often surface strongly. If unneutered males are housed together, their territoriality escalates into significant aggression, often resulting in serious fighting. For this reason, standard recommendations for keeping companion mice emphasize housing females together or housing males only if they are neutered to prevent these predictable, violent confrontations.