Flying squirrels produce a surprisingly rich variety of sounds, from soft chirps and trills that human ears can pick up to ultrasonic calls pitched well above anything we can hear. Research on North American species has documented anywhere from 10 to 27 distinct audible call types depending on the species, and at least four types of ultrasonic vocalizations with peak frequencies sometimes exceeding 60 kHz. That dual repertoire, one channel audible and one hidden, makes flying squirrels among the more vocally complex rodents studied so far.
The Audible Calls You Might Actually Hear
If you live near woods with flying squirrels, the sounds you are most likely to notice at night are high-pitched chirps, trills, and short barking notes. A detailed study of captive northern flying squirrels (Glaucomys sabrinus) and southern flying squirrels (Glaucomys volans) distinguished 10 call types in the northern species and 27 in the southern species, with nine of those call types shared between the two.1Journal of Mammalogy. Vocal repertoire of captive northern and southern flying squirrels (Glaucomys sabrinus and G. volans) That gap is notable. Southern flying squirrels appear to have a much more elaborate vocal toolkit than their northern cousins, though some of the difference could reflect the difficulty of recording every call type a wild animal produces.
For northern flying squirrels, the most frequently recorded calls were upsweeps (about a quarter of all calls), arc chirps (another quarter), and trills (roughly 23%), with tonal chirps and two-toned chirps rounding out the top five.1Journal of Mammalogy. Vocal repertoire of captive northern and southern flying squirrels (Glaucomys sabrinus and G. volans) Southern flying squirrels leaned more heavily on trills, which made up nearly 38% of recorded vocalizations, followed by barks at about 14% and arc chirps at around 11%.1Journal of Mammalogy. Vocal repertoire of captive northern and southern flying squirrels (Glaucomys sabrinus and G. volans) In plain terms, trills are rapid, pulsing notes that sound a bit like a tiny motor running, while chirps are shorter, cleaner tones. Barks are abrupt and percussive. One call type, the growl, was recorded only from northern flying squirrels and not from southern ones.
To a casual listener outdoors, many of these calls blend together into a rapid, high-pitched chatter. The individual call types are easier to tease apart on a spectrogram than by ear, because flying squirrel vocalizations tend to be quiet relative to, say, a gray squirrel’s alarm bark, and they happen fast. If you hear a series of quick, birdlike chips or a soft trilling from a tree cavity after dark, you may well be hearing a flying squirrel rather than a nocturnal bird.
The Sounds You Cannot Hear
The more remarkable part of the flying squirrel vocal repertoire is the one we had no idea about until relatively recently. Researchers recording northern and southern flying squirrels with ultrasonic microphones discovered that both species produce vocalizations well above the roughly 20 kHz ceiling of human hearing.2PLoS ONE. Ultrasonic Vocalizations Emitted by Flying Squirrels Four distinct ultrasonic call types have been described in laboratory and field recordings.
The first type is a short burst of broadband noise lasting 20 to 40 milliseconds, with peak frequencies regularly exceeding 60 kHz. There is no clear tonal structure to it; think of it as a brief blast of static pitched far above what any human could detect.2PLoS ONE. Ultrasonic Vocalizations Emitted by Flying Squirrels The second type is a longer, more complex signal that starts with strong pulses of amplitude modulation and then settles into a wavering, frequency-modulated tone oscillating between roughly 19 and 27 kHz. That puts at least part of the signal near the edge of human hearing in theory, though in practice most people would not detect it.
A third type was recorded only from a male southern flying squirrel in the presence of a female. It consisted of a two-note signal: a short upward sweep from about 55.6 to 58.5 kHz, immediately followed by a steady tone at around 53.7 kHz.2PLoS ONE. Ultrasonic Vocalizations Emitted by Flying Squirrels That mating context hints at a courtship function, though the sample was small. The fourth type, recorded at a nest cavity, was a rapid downward sweep from about 51 kHz to 28 kHz in just 10 milliseconds, entirely ultrasonic.
These findings pushed flying squirrels into a small club of rodents known to use ultrasound for communication. Mice and rats have long been studied for their ultrasonic calls, but the discovery in flying squirrels was unexpected partly because squirrels in general were not thought to vocalize much above the audible range. The fact that some of these calls are purely ultrasonic, meaning no part of the signal dips into the range a human ear could pick up, suggests that flying squirrels have an entire communication channel that went completely unnoticed until researchers pointed the right microphones at them.
What the Calls Mean
Researchers studying squirrel vocal behavior broadly categorize calls by the situations in which they are produced. A review of vocal communication across squirrel groups, including flying squirrels, identified several behavioral contexts linked to specific call types: alarm, aggression, discomfort, affiliative or social bonding, mating, and calls made by newborns.3Ecosphere. Behaviors associated with vocal communication of squirrels In flying squirrels specifically, the evidence is still catching up to the catalog of known call types, but some patterns are becoming clear.
Trills, the most common call for southern flying squirrels and among the top calls for northern ones, seem to serve a social bonding or spacing function. Flying squirrels are more social than many people realize, sometimes nesting communally in winter for warmth. Trills are frequently recorded at or near nest sites, and their complex structure may help individuals recognize each other. Barks and sharp chirps are more commonly recorded in contexts that suggest alarm or territorial defense, much like the alarm calls of daytime squirrel species. The ultrasonic call recorded from a male in the presence of a female is a strong candidate for a courtship signal, though so few examples have been captured that researchers are cautious about assigning a definitive function.
Juvenile southern flying squirrels produce their own distinctive sounds. Trills and tonal pings were recorded from young animals in captivity, and neonatal calls in rodents generally serve to attract the mother’s attention or signal distress.1Journal of Mammalogy. Vocal repertoire of captive northern and southern flying squirrels (Glaucomys sabrinus and G. volans) Whether those juvenile calls include an ultrasonic component has not been well studied yet, but given how widespread ultrasonic calling is in infant rodents of other species, it would not be surprising.
Seasonal and Nightly Patterns
Flying squirrels do not call at the same rate year-round. A study of Humboldt’s flying squirrel (Glaucomys oregonensis), a species only formally described in 2017, tracked ultrasonic vocal activity across seasons at two locations in California. Trills, the most structurally complex of the four main call types monitored, were produced at higher rates in summer than in winter at both sites.4PubMed Central. Seasonal variation in the ultrasonic vocal activity of Humboldt’s flying squirrel (Glaucomys oregonensis) The timing lines up with the breeding season, which supports the idea that trills play a role in mate attraction or pair-bonding.
The three simpler chirp-like call types, arc chirps, tonal chirps, and upsweeps, showed a different pattern. At the San Bernardino site, these calls were given at greater rates in summer, but at the Humboldt County site, rates did not change much between seasons.4PubMed Central. Seasonal variation in the ultrasonic vocal activity of Humboldt’s flying squirrel (Glaucomys oregonensis) The geographic difference is interesting. It could reflect different population densities, habitat structures, or local food availability influencing how much the squirrels need to communicate. The researchers also found that nightly activity patterns, meaning when during the night the squirrels called most, shifted between seasons in both locations. Flying squirrels may use certain call types earlier or later in the night depending on their function, with mating-related calls peaking at different hours than territorial or alarm calls.
For anyone trying to hear or record flying squirrels, the practical takeaway is that summer nights tend to be noisier. If you set out with an ultrasonic detector in winter, you will likely pick up fewer calls and may need to spend more nights listening.
How Researchers Detect Flying Squirrels by Sound
The discovery of ultrasonic calling opened up a practical application: using bat detectors and similar ultrasonic recording equipment to survey for flying squirrels in the wild. Traditional survey methods for flying squirrels involve live-trapping or nest-box checks, both of which are labor-intensive and can disturb the animals. Acoustic surveys offer a less invasive alternative, and they have proven more efficient for detecting the presence of flying squirrels in a forest patch.5Wildlife Society Bulletin. Using ultrasonic acoustics to detect cryptic flying squirrels: Effects of season and habitat suitability
The approach matters especially for the endangered Carolina northern flying squirrel, a subspecies restricted to high-elevation spruce-fir forests in the southern Appalachians. Researchers found that the best time for acoustic surveys of this subspecies is during spring, with six to ten nights of recording at sites with suitable habitat.5Wildlife Society Bulletin. Using ultrasonic acoustics to detect cryptic flying squirrels: Effects of season and habitat suitability Habitat quality turned out to be important: in lower-quality habitat, detection rates dropped and longer survey periods were needed. Season mattered too, though the study indicated that flying squirrels could be detected acoustically in any season with enough survey effort.
This kind of passive acoustic monitoring is the same basic technology used for bat surveys, and the fact that flying squirrels and bats overlap in frequency range (many bat echolocation calls fall between 20 and 100 kHz) means that researchers sometimes pick up flying squirrel calls while conducting bat studies. Learning to tell the two apart on a spectrogram is becoming a useful skill for wildlife biologists working in forested habitats at night.
Why Southern Flying Squirrels Are So Much Louder (Vocally Speaking)
The disparity between 10 audible call types in northern flying squirrels and 27 in southern flying squirrels deserves a closer look, because it is one of the more puzzling findings in flying squirrel bioacoustics. Southern flying squirrels are smaller, more widely distributed, and found at lower elevations across most of the eastern United States and into Central America. Northern flying squirrels occupy boreal and montane forests across Canada and the northern tier of the United States. The two species overlap in range through parts of the Appalachians and the Great Lakes region.
One possible explanation for the richer vocal repertoire in the southern species is that southern flying squirrels tend to be more social. They are well documented to nest communally, sometimes with a dozen or more individuals sharing a single tree cavity in winter. More social complexity often comes with more nuanced communication. Animals that frequently interact with group members in cooperative or competitive contexts tend to evolve finer distinctions in their vocal signals, so the larger repertoire could be a reflection of a more socially demanding lifestyle.
Another possibility is simply that the southern species has been studied more extensively in some settings, and more observation time turns up rarer call types. The researchers who documented the 27 call types noted that nine of them were shared between the species, meaning the basic building blocks of the repertoire are similar.1Journal of Mammalogy. Vocal repertoire of captive northern and southern flying squirrels (Glaucomys sabrinus and G. volans) The southern species may have elaborated on those shared elements, subdividing calls into more context-specific variants. This is speculative, but it fits a broader pattern in animal communication research where closely related species with different social structures show measurable differences in vocal complexity.
What You Will Hear If a Flying Squirrel Moves Into Your Attic
Flying squirrels are common attic inhabitants across much of North America, and people who share their home with them often become aware of the animals through sound before they ever see one. The noises most homeowners notice are not the vocal calls described above but rather the mechanical sounds of small animals moving around: scratching, scurrying, and the soft thump of landing after a glide. Because flying squirrels are nocturnal, these sounds tend to start after dark and can continue through the night, which distinguishes them from gray squirrels and red squirrels that are active during the day.
The vocal sounds that carry through walls and ceilings are usually the higher-pitched chirps and chattering, which can be faint enough to mistake for a bird. If you hear rapid, high-pitched squeaking from your attic at two in the morning, flying squirrels are a strong possibility, especially if you also hear the patter of small feet on wood or insulation. The ultrasonic calls, of course, pass through the walls without anyone noticing.
People sometimes confuse flying squirrel sounds with those of mice or bats. Mice tend to produce lighter, more sporadic scratching and rarely vocalize loudly enough to hear through a ceiling. Bats in an attic make a distinctive fluttering and rustling sound that is quite different from the pattering of feet. Flying squirrels are also considerably more social than either mice or bats in a typical attic setting, so if you hear what sounds like multiple small animals chasing each other and chattering back and forth, that social dynamic is a useful clue.
The Third North American Species
Until 2017, North America was thought to have just two flying squirrel species, the northern and the southern. Genetic analysis then split what had been the Pacific coastal populations of the northern flying squirrel into a distinct species: Humboldt’s flying squirrel (Glaucomys oregonensis). This third species lives along the Pacific coast from southern British Columbia into California, and its vocal behavior is now being studied in its own right.
Early results show that Humboldt’s flying squirrel produces the same general categories of calls as its relatives, including arc chirps, tonal chirps, upsweeps, and trills that extend into ultrasonic frequencies.4PubMed Central. Seasonal variation in the ultrasonic vocal activity of Humboldt’s flying squirrel (Glaucomys oregonensis) Whether the fine details of those calls differ enough between species to serve as an acoustic species identifier is an active area of research. If so, it could make wildlife surveys faster and cheaper: instead of trapping a squirrel and measuring it or running a genetic test, a biologist could record its calls and classify it by voice. That kind of acoustic fingerprinting is already standard practice for many bird and bat species, and flying squirrels may be headed in the same direction.
For now, the vocal world of flying squirrels remains partly unexplored. The ultrasonic dimension was only confirmed in 2013, and seasonal calling patterns in Humboldt’s flying squirrel were published as recently as 2024. Each new study tends to add call types to the catalog or refine the behavioral context for calls that were previously recorded without much situational detail. Given that roughly 50 species of flying squirrel exist worldwide, most of them in Asia, the chances are good that researchers have barely scratched the surface of what these animals are saying to each other in the dark.