FLYING SQUIRREL: CHARACTERISTICS, HABITAT, NUTRITION, BEHAVIOR - BIOLOGY - 2024

The flying squirrels are a set of genres that make up the flying squirrel family Sciuridae tribe. These squirrels are arboreal animals that have developed a special form of locomotion that consists of gliding or gliding through the air between trees.

The Pteromyini tribe is a group of ancient rodents that are now mainly distributed to South and Southwest Asia, with some endemic species in North America and Europe. This tribe of squirrels forms a monophyletic group that evolved from tree squirrels.

Southern Flying Squirrel (Glaucomys volans) By Cephas

Currently, the Pteromyini tribe represents about 15% of the animals belonging to the Sciuridae family.

In contrast, fossil records indicate that millions of years ago, flying squirrels were a more diverse group than "common" squirrels. To date, around 70 fossil species belonging to the Pteromyini tribe have been reported. Furthermore, its distribution was much wider than today.

Flying squirrels probably originated in Europe during the transition between the Oligocene and the Miocene. After appearing, they spread to North America and Asia, diverging into a wide variety of species. At the end of the Miocene, the northern hemisphere suffered a climatic deterioration that caused a decrease in the diversity of species of the Pteromyini tribe.

On the other hand, conditions in South and Southeast Asia formed forested regions that served as diversification centers for flying squirrels during the Quaternary glacial period.

The events of connection and separation of habitats in the Asian territory, promoted the speciation of these squirrels. At present, 44 living species distributed in 15 genera are recognized. Some researchers consider that the Pteromyini tribe is divided into three monophyletic groups that share certain morphological characteristics: Petaurista, Trogopterus and Glaucomys.

General characteristics

Flying squirrels, like other squirrels, have a slender body and a long tail with abundant fur. These squirrels are characterized by having a membrane on each side of the body, between the front and rear extremities.

Unlike flightless squirrels, they have longer limbs and shorter hands and legs, as do the distal vertebrae of the spine.

The size among the species of flying squirrels is very varied, ranging from 24 grams, of the pygmy flying squirrel of the genus Petaurillus, to 1.5 kilograms of the giant Petaurista flying squirrel.

Small squirrels have broad tails with longer side fur compared to dorsal and ventral fur. In addition, they have a small or absent uropathy (membrane) between the hind limbs and the tail.

Large squirrels, on the other hand, have uniform fur over the entire surface of the tail, which is usually rounded and long. These squirrels have a large uropathy.

The Petaurista and Trogopterus groups have more complex teeth, associated with the folivory of these groups. In contrast, the Glaucomys group has suffered dental simplifications throughout its evolution.

Sliding adaptations

The species of the Pteromyini tribe developed a membrane made up of skin and short fur called patagio. This membrane extends in the lateral region on both sides of the body, from the wrists to the ankles.

Additionally, in flying squirrels there is a styliform cartilage that extends laterally from the carpus in the hands and supports the gliding membrane or patagium. This structure is absent in other mammals that use the same method of locomotion, such as the flying lemur and the flying fox.

Styliform cartilage forms an aerodynamic structure in conjunction with the hands, which allow controlling the movements of the patagium during gliding. The movement of the wrists also allows to control the rigidity of the patagium and the direction of the slide during the descent.

The tail of these animals is long and has a certain stiffness, which gives them an aerodynamic profile.

Flying Squirrel Patagio Outline By ScottForesman

Evolution of landslide

In ground and tree squirrels, the semitendinosus muscle of the thighs has two heads, one originating from the ischium and the other from the first caudal vertebrae. Said muscle, in flying squirrels, has a third head that originates from the distal part of the tail.

The origin of the third head is located more distally in the tail in squirrels with highly developed uropathy. In general, the semitendinosus muscle attaches to the lower hind limbs and runs along the edge of the uropathy.

The specific insertion site and origin of this muscle varies between genders and has migrated to the more distal regions of the tail as flying squirrel species have evolved.

On the other hand, the tibiocarpalis muscle, which is absent in flightless squirrels, originates from the ankle and extends to the styliform cartilage. In larger species, the origin of this muscle is in the foot.

In this sense, the largest species appear to be the most evolutionarily derived. This means that flying squirrels come from an ancestor more anatomically similar to today's small flying squirrels. In the following video you can see how the flying squirrels plan:

Habitat and distribution

Distribution

Squirrels of the Pteromyini tribe are distributed in North America and Eurasia from the northern coniferous forests to the tropical lowlands. Most of the species are found in southeast Asia.

With the exception of the species Glaucomys volans, G. sabrinus, G. oregonensis and Pteromys volans, the other species of flying squirrels are distributed in Asia. This continent is considered to have a peak of species diversity (hot spot) reaching the maximum richness towards the southeast.

Species of the genus Glaucomys are distributed in North America west of Oregon (G. sabrinus and G. oregonensis) and from Canada to Florida, with records in Mexico, Guatemala and Honduras (G. volans).

The species P. volans is the only one found in Europe, north of the continent on the east coast of the Baltic Sea, in Estonia, Finland and Latvia.

In Asia, 17 species are found in Malaysia, 14 in Thailand, 13 in Indonesia, 13 in India, 11 in Brunei, and 10 in China.

Habitat

Asian flying squirrels are distributed between 800 and 4000 meters of elevation, preferring subtropical humid forests with dense canopies. In North America and Europe they have been recorded in coniferous forests and deciduous forests.

The strictly arboreal habits of these squirrels, in addition to their sensitivity to climatic changes, make these animals good indicators of the conditions of wooded habitats. In this way, flying squirrels are used in studies on speciation and changes of habitats with respect to climatic changes.

Giant Indian flying squirrel (Petaurista petaurista) gliding through trees By Pratik Jain

Taxonomy and classification

The group of flying squirrels was separated from the rest of the squirrels in 1855 by Brandt, who placed them within the subfamily Pteromyinae, without excluding them from the family of arboreal and terrestrial squirrels Sciuridae.

In 1893, Major relocated the flying squirrels along with the flightless ones in the Sciurinae subfamily. On the other hand, in 1912 Muller coined the family Petauristidae, separating the flying squirrels from the family Sciuridae.

By the second half of the 19th century, the term Pteromyinae was recognized as the valid taxonomic level for flying squirrels. However, some genetic studies conducted in the early 21st century revealed that flying squirrels are not sufficiently differentiated from flightless ones to form a subfamily.

In this way, this group of squirrels was demoted to the tribe level (Pteromyini) and included again in the Sciurinae subfamily, along with other tree squirrels.

Taxonomic history

The taxonomy of flying squirrels has been complex since its discovery. Linnaeus initially described two species in 1758: the European flying squirrel Sciurus volans and the North American as Mus volans.

Later, both were located in the same genus Sciurus and Pallas in 1778 named the North American squirrel as Sciurus volucella, a name that he maintained until 1915. During the 18th century, four other species were described, three of which remained within the genus Sciurus, and the fourth in the genus Petaurista coined by Link in 1795.

In the 19th century George Cuvier transferred all flying squirrels to the genus Pteromys, thus separating them from the common arboreal and ground squirrels (of the genus Sciurus). A second genus was coined by Frédéric Cuvier in 1825 (Sciuropterus).

Towards the end of the 19th century, the genera Pteromys, Sciuropterus, Eupetaurus, Petaurista and Trogopterus existed.

Classification in the 20th century

The genus Sciuropterus was divided at the beginning of the 20th century into nine genera: Trogopterus, Belomys, Pteromyscus, Petaurillus, Iomys, Glaucomys, Hylopetes, Petinomys, and Sciuropterus.

In 1915 Howell divided the genus Glaucomys into Eoglaucomys for Himalayan flying squirrels and Glaucomys for North Americans. Later, Pocock elevated Hylopetes and Petimomys to genera. In 1914 Sciuropterus came to be considered a synonym for Pteromys.

Finally, with the description of three more genera, Aeromys (Robinson and Kloss, 1915), Aeretes (Allen, 1940) and Biswamoyopterus (Saha, 1981) the current taxonomic arrangement with 15 genera and more than 40 species was formed.

Petaurista alborufus. China Giant Flying Squirrel By lonelyshrimp

Current ranking

Currently the 15 recognized genera are grouped into two subtribes: Glaucomyina and Pteromyina.

Glaucomyina subtribe

- The genus Glaucomys includes three species endemic to North America: volans, sabrinus, and oregonensis.

- In Malaysia and Indonesia the genus Iomys includes the species horsfieldi and sipora.

State of conservation

During the last decades, flying squirrel populations have suffered a marked decline due to deforestation and degradation of primary forests, as well as sport and illegal hunting.

Species of the genera Glaucomys and Pteromys are classified by the IUCN as “least concern” (LC) since their populations have remained stable.

North American flying squirrels are widely distributed and their populations are stable, although habitat destruction and disturbance may decrease some populations. These disturbances cause the loss of trees with cavities that serve as shelter for these squirrels.

There has been a decrease in some populations of G. sabrinus south of the Appalachians, due to a vermiform parasite (Strongyloides robustus) that causes weakness and death in these squirrels.

On the other hand, these squirrels are becoming more and more popular as pets and although they are generally commercialized from hatcheries, their poaching and illegal trade could pose a threat to these species.

Pteromys volans, on the other hand, has shown a decrease of 30% to 50% in some populations of its range in the last decades, due to the loss of ancient mixed forests.

Conservation status in Asia

In Asia, most species are in the IUCN “Least Concern” category.

However, some species such as Belomys pearsonii, Petaurista nobilis and P. magnificus are in a “vulnerable” state due to loss of habitat due to activities such as mining, illegal logging, deforestation, monocultures, human settlements and construction. They are also frequently hunted for consumption.

Other species such as Petinomys fuscocapillus are listed as “near threatened”, with habitat degradation being their greatest threat. Furthermore, illegal hunting for medicinal purposes and to market their skin are common causes of population decline.

The species Biswamoyopterus biswasi and Eupetaurus cinereus are critically endangered, mainly due to the loss of food resources as their habitats have been replaced by crops for human use. They are also highly hunted for consumption.

Reproduction

Flying squirrel reproduction is limited to one or two reproductive periods per year, usually during the spring. The periods with long photoperiods coincide with an inhibition of testicular descent in males, which indicates that the reproductive periods are related to variations in temperature and length of the day.

In Glaucomys volans reproductive peaks have been recorded, with the production of numerous litters in the months of April and August. Mating occurs between February and March and in July. Gestation lasts 40 days. Litters can be from two to four individuals per parturition.

The young are born without fur and with very light skin. They develop fully at six weeks, during which time they are frequently breastfed by their mothers. Between six and 10 weeks of age, squirrels are fully developed and separated from their parents.

Nutrition

Flying squirrel feeding on Ficus fruits By Vickey Chauhan

Flying squirrels are opportunistic omnivores. This means that they feed on the resources that are mostly available in their habitat. The consumption of seeds, leaves, flowers, fungi and some invertebrates such as arachnids, insects and snails is common.

Some groups of squirrels, such as Petaurista and Trogopterus, feed mainly on the leaves of trees such as Ficus racemosa, Cullenia exarillata and Artocarpus heterophyllus. The consumption of leaves in some of the species in these groups represents up to 33% of their diets.

Other species of some genera such as Glaucomys consume a large quantity of hypogeal fungi and lichens, representing up to 90% of their diets. These squirrels are important nocturnal dispersers of spores and seeds of plant species.

Behavior

Most species of flying squirrels have twilight and arboreal habits. They often create shelters in solid wood tree holes and rock holes on cliffs and precipices.

These animals, in general, are not very adept at fleeing predators such as raptors, tree snakes, and raccoons. Because of this, these squirrels developed nocturnal habits.

Flying and flightless squirrels have similar habits when it comes to using resources such as building shelters and nesting in tree cavities. However, flying squirrels avoid competition for resources, choosing higher shelters away from other trees.

These squirrels also present aggregations between individuals of different ages and sexes. Aggressive behaviors have not been recorded among breeding males.

The females form aggregations during the cold months, but they become very territorial when they have their young, so they can become aggressive if an adult gets too close to the shelter where they protect their litters.

References

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