Southern Flying Squirrels

Southern flying squirrels (Glaucomys volans) can be found in southeastern Canada, the eastern United States, and Mexico into Honduras and are reputed to be as common as gray squirrels (Scuirus carolinensis), so why is it that every time we mention them the typical response is "flying what?" The answer is that these diminutive and elusive squirrels are a nocturnal rodent species that glide silently through the woods while most of us are sleeping. Loggers, rehabbers, and bird watchers are virtually the only people who experience the privilege of ever encountering them.

We have been recording the behaviors (nightly) of free-roaming Southern flying squirrels at the Brookside Nature Center, Wheaton, Maryland, since September 1993. Our data has been collected from three separate feeding stations. We have become enchanted by these little squirrels and would like to share the knowledge we have gained.

To begin, we first had to locate the squirrels, which was not an easy task due to their shy and elusive nature. Nightly attempts to locate them from September through November 1993 were unsuccessful. We went out each night starting in February 1994, but did not have our first sighting until April 14th. Flying squirrels are cautious and maintain a vigilant guard against danger or intrusion from either man or animal. They are very sensitive to disturbances in their environment and take flight in response to air traffic, barking dogs, the cry of a human infant, owl vocalizations, the approach of observers, terrestrial predators (cats, raccoons) and other flying squirrels.

Optimum environmental conditions that resulted in highly successful flying squirrel sightings were: nights marked by light rain, heavy cloud cover, fog, and mild evening temperatures. Nights of intense humidity combined with active storms (resulting in a "rising steam" effect) also lent themselves to successful sightings. The flying squirrels were most active on nights of poor visibility, which may possibly be an anti-predator defense mechanism.

Flying squirrels become active right at nightfall. They forage nightly except when any of the following environmental factors are present: nights of heavy rain prior to foliage development; nights with strong, gusty winds; lightning; the presence/vocalizations of owls, and bright moon-lit nights. They would not come to the feeders if there was loud human activity nearby (picnickers, scout groups, etc.)

Their natural diet includes acorns (hickory) nuts, twig bark, lichens, fungi, fruits and berries, some insects and meat. We provided sunflower seeds nightly to attract the squirrels and occasionally offered mealworms. Both of these food types were readily consumed at the feeder. In midsummer we began smearing peanut butter, with sunflower seeds pressed into it, on the feeder backboard and on the tree bark below the feeders when the population increased as a result of the spring and summer birthings. This allowed more squirrels to feed simultaneously and provided us with the opportunity to record social interactions. Almonds were provided in the fall, in addition to the sunflower seeds. Hoarding is a priority from September through early December. Almonds were almost always taken to another location to be eaten or stored. We occasionally offered canned pet foods with the seeds, and although it attracted increased numbers of squirrels to the feeders, they were never observed eating it. Canned pet foods also attracted raccoons to the feeder.

The raccoons not only took over the feeder to eat, but then would lie on the platform and take a rest, thereby keeping the squirrels from the food.

The squirrels' responses to danger was dependent on whether the threat was from a terrestrial or aerial species. When the danger was from a terrestrial species, the squirrels quickly ascended the tree and emitted three successive single-note squeaks. When it was aerial, the squirrels either descended the tree bark, raced to the back of the tree, or relocated deeper into the woods where foliage cover was more dense. In either case it was common for the squirrels to vocalize continuously and quite audibly for up to 20 minutes.

Flying squirrels use different vocalizations, or variations of the same vocalization, in response to different situations. Soft, weak-sounding squeaks were heard in the spring, summer, and fall, and indicated the presence of nest-bound squirrels. High-pitched squeaks were used by juvenile, subadult, and adult flying squirrels. A repeated single note squeak was heard whenever a flying squirrel was driven away from the feeder and was made by the retreating squirrel. The double-note squeak was only heard as a response to the presence of an aerial predator. The triple-note squeak was always heard when a flying squirrel was startled by the approach of other flying squirrels, observers, and by the approach of terrestrial predators.

Molting occurred in early July and always began at the squirrel's lower back. Additionally, we noted huge, bulbous swellings, predominantly around the genital area but not exclusive to it. One squirrel had a huge swelling on its forehead, between its eyes. These swellings are thought to be an infestation by Bott fly larvae, which does not kill its host but rather completes a stage of life cycle while on the host.

Aggression among the flying squirrels peaked in August. There was conflict among the juveniles and between mothers and their offspring. There are multiple factors at this time. The population count was up as a result of the spring and summer birthings. The next breeding season was a month away and mothers were encouraging their young to become independent. Two of our feeders had been overtaken by raccoons, who not only ate the peanut butter and sunflower seeds but then slept on the feeders.

When a mother flying squirrel realized the location of her nest-bound infants had been discovered, she moved the infants within 24 hours. Flying squirrel offspring accompanied their mother on foraging trips at about five weeks of age. Usually the mother would bring all of her infants to the feeders at one time, but it was not uncommon to see a female with only one infant the first night, two to three infants the next night, and then four infants by the third night. Infants also dispersed from their natal area at staggered intervals. Fall litters dispersed earlier than spring and summer litters and was most likely an artifact of the heavy owl predation we experienced in September and October as well as the shortened daylight hours.

Female flying squirrels average four infants per birthing. They fiercely protect their offspring and demonstrate extreme patience with them but only for the first five weeks.

The mature adult females gave birth between 19-21 July. They returned to the feeders on 23 July. It is at this time that mothers become less tolerant of the offspring from the previous litter. This intolerance escalates to a level of full blown aggression over the food. During the 3-4 day period that the mature females were giving birth, we were unsuccessful at locating any of the juvenile and subadult flying squirrels (we average 23 flying squirrels a night) which suggests that they play some role in the birthing by the mature adult females.

The pregnant subadult females gave birth a few weeks later, thereby staggering the birthings and resulting in two distinctly different aged juveniles at the feeder trees. The older juveniles would not allow the smaller infants to use the feeder simultaneously, but would allow them to remain on the tree and wait their turn to feed.

Two related females shared the same home tree throughout the year. They both raised a spring and summer litter in that tree, but we cannot confirm whether they shared a birthing nest or just the home tree. These two females were seen together nightly from spring until the fall when they foraged separately after their maternal duties were completed. There were three birthings during the year, but the females that gave birth in the spring and summer were not the females that gave birth in the fall.

Male flying squirrels were only seen in association with females when the male was an offspring traveling with its mother and siblings. Naturalist Rob Gibbs, BNC, has documented in his study on nest box use, that male flying squirrels tend to use nest boxes and can be found in bachelor groups. Female flying squirrels seem to prefer tree cavities during late spring and up until winter when they were found sharing nest boxes with males during the winter months.

Adult flying squirrels that wee accustomed to the supplemental feeders occasionally came down to eat shortly prior to nightfall, but juvenile flying squirrels never came down to the feeders until dark. Adult squirrels also did not come to feeders when there were owls nearby but juveniles did take the risk.

Flying squirrels do not truly "fly"; they glide from tree to tree. They are such accomplished gliders that they can veer around objects and resume the original direction of their glide. One evening we observed them performing "zig-zags" during their glides. Published literature states that they ascend very high on a tree before gliding off, but we can verify that they can catapult off at any height and successfully complete a horizontal glide.

Flying squirrels are territorial and will not tolerate non-related squirrels on their tree. In fact, even kin-related squirrels must endure a brief period of conflict until they are recognized as kin and allowed to remain at the food source. Kinship appears to be an important factor among flying squirrels, and we believe that when a population is discovered in the woods the individuals are an extended family rather than unrelated individuals.

We believe flying squirrels are a female-based society with a complex and fascinating social system. In the fall of 1994 one well-known mother gave up her right to the feeder so her daughter could feed a late season litter of infants. In the spring of 1995 we noted that two of our confirmed mother flying squirrels from 1994 had relinquished their home tree to a daughter and had taken up new residence in a nearby tree.

There is a debate among researchers as to whether flying squirrels enter torpor, a type of pseudo-hibernation. The flying squirrels at the Brookside Nature Center could not be located from mid-December until March in both 1993 and 1994 (during which time we experienced flying squirrel withdrawal). The squirrels returned to the feeders mid-March of 1994 and 1995. We believe that the months in which births occur, the number of birthings, the timing of infant dispersal from the natal area, and whether flying squirrels enter torpor or not are all dependent on the geographic range where they are found.