08/18/2026
Muskrats build reusable air stations under frozen lakes by breathing out as they swim. The exhaled bubbles collect against the underside of the ice along their travel routes. On the return trip, the muskrat stops at each bubble, shoves its nose into it, and inhales whatever oxygen remains. Researchers who documented the behavior estimated it roughly doubles the time a muskrat can spend underwater during winter, turning a dangerous swim between the lodge and a feeding area into a series of short hops between rest stops the animal built with its own breath.
The behavior was confirmed through direct observation and published by MacArthur and Krause in 1992 in the Canadian Journal of Zoology. Observers had noticed bubble trails under the ice for years and assumed they were simply exhaled air left behind by swimming muskrats. The discovery was that the muskrats were going back and using them.
A muskrat swimming beneath the ice would stop at a cluster of trapped bubbles, press its snout against the underside of the ice where the air had collected, and inhale. Then it continued to the next cluster. The route between the lodge and the feeding area became a corridor of breath stops, spaced at intervals determined by wherever the muskrat had happened to exhale on a previous trip.
The system solves a problem that kills muskrats every winter. A muskrat's lodge sits above the waterline with underwater entrances. The animal leaves through the water, swims beneath the ice to reach submerged vegetation, feeds, and swims back. If the distance between the lodge and the food is farther than the muskrat can travel on one lungful, it drowns. In shallow marshes where the ice is close to the bottom, the problem is worse because the reduced water volume means less dissolved oxygen. The bubble stations extend the range by giving the muskrat intermediate breathing points along its commute that did not exist until the muskrat created them.
The bubbles lose oxygen over time. Each reuse extracts some of the remaining air. Fresh bubbles from a recent trip hold more oxygen than old ones from a trip made days earlier. The system works best on routes the muskrat uses frequently, where the bubbles are replenished regularly by repeated exhalations along the same path. A well-traveled route between a lodge and a prime cattail stand becomes a maintained infrastructure of air pockets, refreshed with every pass, degraded by every breath, and functional as long as the traffic continues.
A muskrat prepares for winter water differently than it prepares for summer water. Chuck Lura, writing for Prairie Public's Natural North Dakota, described a behavioral shift that researchers had measured: muskrats elevate their body temperature by roughly one degree before entering the water during winter. They do not do this in summer. The mechanism has not been fully identified, but it may be related to the hyperventilation observers have documented in muskrats immediately before winter submersion.
The animal also grooms obsessively before and after each swim, distributing water-repellent oils through its pelt that trap air against the skin for insulation. The grooming itself generates body heat. A muskrat entering winter water has pre-heated its body, waterproofed its fur, hyperventilated to load its blood with oxygen, and mapped out a route beneath the ice where its own previous breaths are waiting.
Image is for illustration purposes only
Source: MacArthur and Krause (1992), Canadian Journal of Zoology / Prairie Public, Natural North Dakota / Chuck Lura.
