House mice arrived in Massachusetts with European colonists and NatureServe still classifies them as exotic rather than assigning any conservation status. They thrive around buildings, farms, and disturbed ground, so records near Great Meadows National Wildlife Refuge and Walden Pond State Reservation more likely trace back to nearby structures and field edges than to the wetlands and woods those sites are named for.
Records peak in March, roughly four times the low months of late fall, a pattern that probably reflects breeding activity picking up as winter eases rather than a true summer or fall high. House mice breed year-round indoors, so outdoor sightings depend heavily on when populations spill out of buildings into open ground.
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