The yellow-bellied marmot (Marmota flaviventris) — also called the "rockchuck" throughout much of Montana — is the largest member of the squirrel family found in the state. Stocky, powerful, and deceptively industrious, marmots are a beloved sight on rocky hillsides and in alpine meadows, but they become a real problem when they establish burrow systems beneath residential structures, decks, crawl spaces, outbuildings, and landscaped areas.
Marmots are true hibernators, spending roughly half the year — typically September through March or April — in deep hibernation underground. But during their active months, they are relentless excavators. A marmot burrow can extend 5 feet or more below the surface with multiple chambers, dozens of feet of tunnel, and several entrance holes. When this system is established beneath a concrete pad, deck footing, retaining wall, or foundation, the resulting soil displacement and subsidence can cause serious structural problems.
Marmots are also highly social and colonial — where one marmot takes up residence under your deck, others will follow. Their sharp, piercing whistle alarm call is a distinctive Montana summer sound — but it carries a different meaning when it's coming from under your front steps.
Size
18–28 inches; 5–11 lbs
Color
Yellow-buff belly; grizzled brown back
Active Season
April–September (hibernate October–March)
Risk Level
Medium–High (foundation/structural undermining; colonial)
Habitat
Rocky outcrops, hillsides; under decks, foundations, sheds
Burrow depth
5+ feet; multiple chambers and entrances
SIGNS OF INFESTATION
Signs a Marmot Has Moved Under Your Structure
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Large burrow entrance under or near structure — 4–6 inch diameter holes beneath decks, foundation edges, sheds, or concrete slabs, often with a mound of excavated soil.
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Visible animals — Large, stocky, ground squirrel-like animals basking on rocks, decks, or near burrow entrances.
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Whistle alarm calls — A loud, piercing whistle when disturbed; a distinctive and unmistakable sound.
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Soil subsidence near foundation — Soft or sunken areas in soil adjacent to foundation walls, concrete pads, or retaining structures.
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Chewed vegetation — Garden plants, vegetables, and flower beds clipped or consumed close to the ground.
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Multiple entrances — Marmots typically maintain 2–5 burrow entrances; finding several holes in a concentrated area confirms an established colony.
HEALTH RISKS
Marmots can carry plague-infected fleas — the same risk noted for Columbian ground squirrels. They also carry tularemia and can harbor ticks. Direct handling of marmots is not recommended. Any marmot die-off should be reported to Montana Fish, Wildlife & Parks, as mass die-offs can indicate plague activity in the flea population. Use insect repellent when working in or around burrow areas.
PROPERTY DAMAGE
Marmot burrowing beneath foundations, concrete pads, retaining walls, and deck footings creates void spaces in the compacted soil that structural elements depend on for support. Over time, soil settlement into these voids can cause cracking, tilting, and sinking of the overlying structure. For a deck, this may mean uneven or unstable decking; for a concrete slab or foundation, the consequences can be more serious and costly. Garden damage from marmot foraging — consumed vegetables, stripped perennials, and gnawed woody plant stems — is also a common complaint.
