Sugar gliders (Petaurus breviceps) are small nocturnal arboreal marsupials native to New Guinea and the eastern coast of Australia.^1,^5,²⁰ They inhabit open areas in tropical or coastal forests and dry inland sclerophyll tropical forests. They are social animals, with colonies of 6 to 10 animals occupying a territory of up to 1 hectare. Dominant males mark territory and other group members with scent gland secretions. Animals in a group nest communally in leaf-lined tree holes. During periods of extreme cold or food scarcity, sugar gliders conserve energy by going into torpor for as many as 16 hours per day.⁵

Anatomy And Physiology

Marsupials: General Information

Marsupials are best known for possessing a pouch, in which the female raises its young. The degree of pouch enclosure is dependent on the species. The pouch is absent in males and in female South American short-tailed opossums, which are considered to be more primitive marsupials. The female sugar glider has a pouch containing four teats, in which she raises one or two young.

Epipubic bones (ossa marsupialia or eupubic bones) are unique to certain marsupials, but they are diminished or absent in gliders. These small bones are thought to provide an attachment for muscles that support the pouch. Their absence may be an adaptation to gliding, which reduces skeletal weight.

The metabolism of marsupials is approximately two-thirds that of placental (eutherian) mammals. The normal heart rate of a sugar glider is 200 to 300 beats per minute; the respiratory rate is 16 to 40 breaths per minute.¹ The cloaca is a common terminal opening of the rectum, urinary ducts, and genital ducts. Cloacal temperature is lower than the actual body temperature; the average cloacal temperature being 89.6°F (32°C).^1,^4,^8,¹⁰ True rectal temperature in marsupials can be measured by directing the thermometer dorsally into the rectum from within the cloaca. The rectal temperature is usually 97.3°F (36.3°C).⁴ Measurement of the tympanic temperature is another means of determining core body temperature.

Anatomic Characteristics

Wild sugar gliders have soft, velvety fur that is gray, with a central black stripe dorsally; it is cream-colored ventrally. Like American flying squirrels (Glaucomys volaris, Glaucomys sabrinus), sugar gliders have a patagium (gliding membrane) that stretches between their front and hind legs (Fig. 29-1). There are at least seven recognized subspecies of sugar gliders. Although average body weight varies among the subspecies, typical adult males weigh between 100 and 160 g and females between 80 and 130 g. Body length ranges from 16 to 21 cm and tail length from 16.5 to 21 cm. Gliding distances are reported to be as long as 50 m.²⁶ Being a nocturnal prey species, sugar gliders have large, protruding, widely spaced eyes. They have five toes on their hind feet, with an opposable first digit and syndactyly of the second and third digits (Fig. 29-2). Dominant males mark territory and group members with secretions from androgen-sensitive frontal (forehead) (Fig. 29-3), gular (throat) (Fig. 29-4), and paracloacal scent glands (Fig. 29-5).

Fig. 29-1 The patagium, or gliding membrane, of sugar gliders stretches between the front and hind legs.

Fig. 29-2 The hind foot of the sugar glider has five toes, with syndactyly of the second and third digits and an opposable first digit.

Fig. 29-3 The male sugar glider has a frontal scent gland on its head. Secretions from this gland are used to mark territory and group members.

Fig. 29-4 The male glider also has a gular scent gland, located on the ventral aspect of the throat.

Fig. 29-5 Paracloacal glands are most developed in males and may become infected and impacted, as seen here.

Color Variations and Genetics

Sugar gliders have become available in a variety of colors through selective genetic breeding in recent years. Although there has not been thorough genetic testing on these variations, some genetic trends have been realized by applying Mendel’s laws of heredity to well-documented breeding programs. Several color variations have been described and accepted as “standard” mutations. These variations of the natural gray line include the white face, white tip, leucistic, and mosaic. There is also a red-series classification that includes red cinnamon, lion, butter cream, and chocolate.

The white face is not as much a separate coloration as it is a mutation of the stripes around the face. These gliders are missing the black bar below the ears and usually have lighter or broken eye rings. They are the natural gray-and-black coloration otherwise.

The white tip coloration is also just a slight variation of other color varieties. As the name implies, these gliders have white on the ends of their tails. This may indicate the presence of the subspecies Petaurus breviceps ariel in the lineage, but the precise genetic connection is not known. It is believed that the white tip is recessive to normal, but not as a single recessive gene.

The leucistic sugar glider is all white with black eyes; therefore it is also referred to as black-eyed white (Fig. 29-6). Some leucistic gliders may have faint yellowish markings where the black would be on the standard gray coloration. The leucistic gene is recessive to the normal gray, following the principles of Mendelian genetics. The breeding of a heterozygous leucistic to a leucistic yields 50% leucistic and 50% heterozygous. Breeding two heterozygous leucistics can produce heterozygous, standard, or leucistic offspring in the expected ratios. This is a relatively rare and valuable coloration, whether the glider is white or just carrying the gene as a heterozygous leucisitc.

Fig. 29-6 The leucistic sugar glider is also known as the black-eyed white, a rare color variation.

The albino sugar glider differs from the leucistic in that it is all white with red eyes, as seen in other albino animals. As in other species, albinism is the genetic inheritance of recessive alleles manifesting as a lack of melanin pigmentation in the eyes, skin, and hair. These sugar gliders are more rare and valuable.

A mosaic sugar glider has characteristic white patches on the body, feet, or tail. If the mosaic coloration involves the tail, the sugar glider is referred to as a ring-tail mosaic. The mosaic trait is codominant to the standard gray coloration; therefore gliders cannot be heterozygous for the mosaic gene. Certain lines of mosaics may produce sterile males, although the females are fertile. Breeding of mosaics over several generations, however, can breed out the sterile male condition. Mosaic sugar gliders are a relatively rare and expensive color variation.

The red-series gliders are subdivided into four basic colors; chocolate, butter cream, lion, and red cinnamon. These may indeed just be shade variations of the reddish coloration, since these variations are not clearly defined or well established. The chocolate is described as having a brown coat with either brown or black markings. The butter cream has a brown coat with cream to yellow highlights and red or brown markings. The lion is considered to be a standard variation and has a golden brown coat with red markings. The red cinnamon has a reddish coat and red or brown markings. The color of these strains becomes more faded when bred to the standard gray coloration, and the color can be bred out of a line. These colorations are not as valuable as the lighter-colored leucistic or mosaic varieties.

Other color varieties have been described, with more being identified and developed by genetic breeding programs. The variations described above are those more commonly accepted, but they are not fully standardized or genetically defined. As fanciers continue to breed for more unusual mutations and unique colorations, inadvertent selection for genetic disorders and instability is bound to develop as well.

Reproduction

Sugar gliders are seasonally polyestrous, with the natural breeding season in Australia occurring between June and November. They are polygamous, with a dominant male that breeds with the mature females in the colony.⁵ Young (joeys) are typically born in the spring, when insects are plentiful. Litter size is usually two (81%) or, less commonly, one (19%).⁵ Two litters in a single breeding season are common. The estrous cycle is 29 days in length, and gestation is 15 to 17 days.^1,^14,^15,²⁷ Young weigh only 0.2 g at birth, when they migrate to the pouch. They remain in the pouch for 70 to 74 days (Fig. 29-7). After they outgrow the pouch, the young are left in the nest until they are weaned at 110 to 120 days of age. Table 29-1 lists the expected growth rate and specific developmental milestones as the joey ages.^1,¹⁰ The young remain with the colony until they are forcibly dispersed, at 7 to 10 months of age.^1,⁵ Sexual maturity is reached at 8 to 12 months of age in females and 12 to 15 months in males.^1,^14,¹⁵

Fig. 29-7 The female sugar glider raises one or two joeys in its pouch.

Table 29-1 Growth and Development of Young Sugar Gliders ^1,¹⁰

The reproductive anatomy of sugar gliders is unique compared with that of other mammals routinely treated in practice. Female sugar gliders have two uteri and two long, thin, lateral vaginas that open into a single cul-de-sac divided by a septum. Both sexes have paracloacal glands, which are more developed in the male.²⁵ Males have a large prostate with a constriction at the anterior third. They also have two pairs of Cowper’s glands in addition to three paracloacal glands. The testes are located in a prepenile pendulous scrotum, and the penis is bifid (Fig. 29-8). Males do not urinate from the forked end of the penis but rather from the proximal portion. Therefore the distal penis can be amputated in cases of penile trauma or paraphimosis.

Fig. 29-8 In male sugar gliders, the penis is bifid. Male gliders do not urinate from the tip of the forked penis but from its base.

A captive male sugar glider was presented to one of the authors (RDN) with the unusual development of a pouch as well as having the typical bifid penis. This individual lacked a scrotum but may have cryptorchid testes, since he also developed the classic alopecia on the forehead and upper chest present with male scent glands. It is not known if this is a true hermaphrodite, since an abdominal evaluation was not performed to identify a female reproductive tract. It is anecdotally reported that similar gliders have produced offspring and raised them in their pouches.

Behavior

Males develop a scent gland on the forehead and may rub this on the female’s chest. Males also have scent glands on the chest and paracloacal glands. Both sexes mark territory with secretions from scent glands. In addition, the female uses urine to mark territory. The female’s scent glands are within her pouch, and she will secrete and increase marking to indicate breeding readiness to the male.

Sugar gliders are quite vocal, with a whole series of alarm yaps and screams. They are highly social animals and should not be kept as solitary pets; they become clinically depressed when housed singly. Self-mutilation is not uncommon in solitary gliders. Those without proper socialization or exercise and territorial space may become aggressive. Males will fight if there is not enough distance between nest boxes. Both sexes may fight and become irritable at the beginning of breeding. Males without adequate stimulation may become aggressive toward humans. Neutering may help, but they will continue to scent-mark and will not be “human socialized” like a domesticated animal.

Sugar gliders make acceptable pets with the appropriate caretakers if they are given sufficient socialization and ample space. When hand-reared, they adapt well to captivity and develop a strong bond with their human companions. As pets, their care is time-consuming, with recommended socialization periods of at least 2 hours per day. Basic handling for socialization and companionship is best achieved at night, when the animals are more interactive and playful. If awakened and handled during the day, sugar gliders become agitated and irritable.

Sugar gliders are most responsive to and trusting of individuals they know, but they respond well if approached with patience and gentle handling. They enjoy cuddling and curling up in shirt pockets or pouches, where they feel safe. They should not be allowed to crawl into tight-fitting clothes, such as pants pockets, because of the risk of injury.

Advantages of these pets include their small size, playfulness, and intelligence. The life span of sugar gliders is longer than that of other comparably sized pets; they can live from 10 to 12 years in captivity.¹ Disadvantages include their nocturnal nature, housing requirements, specific dietary needs, and musky odor.

Husbandry

Caging

Because of their active nature, sugar gliders should have cages as large as possible. These animals need space to climb, run, and jump. Minimum cage size is 36 × 24 × 36 in. (91 × 61 × 91 cm), but larger is better. Cages should be made of wire for good ventilation, with wire spacing no more than 1.0 × 0.5 in. (2.5 × 1.3 cm) wide. Sugar gliders tolerate temperatures between 65°F and 90°F (18°C and 32°C), with an ideal range of 75°F to 80°F (24°C-27°C).^4,²² The cage must have designated areas for food, water, shelter, and exercise. Several food and water dishes should be placed in various locations throughout the cage. A nest box or sleeping pouch positioned high in the cage gives the sugar glider a place to sleep during the day. Branches, perches, and shelves can be placed at various levels of the cage to satisfy the natural behavior of climbing. Sugar gliders enjoy playing with bird toys, such as swings and chew toys. Plastic wheels without open rungs, such as a hamster wheel, are used for exercise. A variety of objects may be placed throughout the cage to stimulate and entertain these animals.

Sugar gliders need permanent access to a nest box for sleeping and hiding, with minimal daytime disturbances. Nest box size depends on colony size, but boxes should be at least 6 × 6 in. (15 × 15 cm) with a hinged lid and a circular opening on the front with a sliding closure.^1,^5,^16,²² Bird nest boxes or small hollow logs are suitable. Nesting material can consist of hardwood shavings, recycled paper products, shredded bark, dried leaves, coconut fibers, sea grass, or equivalent materials. Artificial wool, cloth strips, and similar materials are not suitable because fibers have been known to entrap an animal’s limbs. Nest boxes must be cleaned and bedding material changed regularly, at least every 1 to 2 weeks. If nest box closures are secure, the nest box can be relocated from an outdoor aviary into the house for interaction each evening and then returned to the aviary to allow for nocturnal activity.

These animals need large areas for activity and exercise, ideally the freedom of a whole room equipped with vertical “trees.” This may be impractical in a typical household, and many owners are reluctant to allow such freedom because gliders scent-mark and are active at night.

Nutrition and Feeding

Natural Diet

Sugar gliders are omnivorous. The diet of a wild sugar glider can include sap and gums (carbohydrate-rich) from eucalyptus and acacia trees, nectar and pollen, manna and honeydew, and a wide variety of insects and arachnids.^5,¹³ Sugar gliders have specialized lower incisors for chewing and gouging into the bark of trees. The lengthened fourth digit on the manus aids in extracting insects from crevices. Sugar gliders also have an enlarged cecum, which functions principally in microbial fermentation of complex polysaccharides in gum.

The diet varies with the season. During the spring and summer months, these animals are primarily insectivorous. During the winter months, sugar gliders feed on gum from the eucalyptus and acacia trees as well as on sap and sugar from the trees and sap-sucking insects. Small insects trapped in wattle or acacia gum are consumed. Favorite trees include the Australian “bloodwood,” the red sap of which crystallizes, mixes with the decaying pulp of the trees, and attracts insect activity. Other trees produce “manna,” a deposit of white encrusting sugars from wounds made by sap-sucking insects, birds, other gliders, or possums. The sugar glider has been observed to eat honeydew, secreted by sap-sucking insects.

Field energetics studies have demonstrated that wild sugar gliders consume 182 to 229 kilojoules (kJ)/day.¹⁹ This is equivalent to approximately 17% of body weight in wet weight of food.¹⁹ Captive gliders expend less energy in exercise and consume more easily assimilated foods than do those in the wild; therefore the total energy offered to gliders in captivity should be less.

Captive Diet

Captive diets must satisfy the numerous specializations of these insectivorous omnivores. The captive diet should include nectar, insects, and other protein sources as well as very limited amounts of fruits and vegetables.^3,^13,¹⁴ Portion size for one glider is roughly a tablespoon of insects or insectivore diet, a tablespoon of nectar, and one-half teaspoon of fruits, other types of insects, etc. The diet should be offered in fresh portions in the evening.

Protein is a critical nutrient in the diet of sugar gliders. Various protein sources include insects (mealworms and crickets), eggs, newborn mice, lean meat, and commercial protein sources (pelleted insectivore diets or monkey chow). Commercially available adult insects should be fed a calcium-rich insect diet for several days before being offered to the gliders. Larval forms should be kept to a minimum.

Approximately 50% of the diet should consist of sources of fruit sugars, preferably in the form of a sap or nectar. Sources include fresh nectar, maple syrup, honey, and artificial nectar products.^3,^13,^14,²² Examples of commercial products include prepared lory diets and Gliderade (Avico, Fallbrook, CA). Gum Arabic (acacia) can be purchased as a powder, mixed into a thick paste, and used to simulate native gums: it can be used in holes in branches and on surfaces, with insects or bits of fruit stuck to it for enrichment and foraging.

Various commercial diets for sugar gliders and insectivores are available and may be included as a part of the diet. Leafy green vegetables provide a source of fiber and some vitamins. Sugar gliders accept a wide variety of other foods, including fruits, vegetables, nuts, and seeds (sunflower and pumpkin), but these should be offered in very limited quantities. Fruit juices and strained baby food can be offered if they are free of preservatives, but they are not as appropriate as the nectar-based formulas. Because these foods are not a significant component of the natural diet, they should constitute less than 10% of the captive diet. Sprinkle a broad-spectrum vitamin and mineral supplement with a good calcium supply on the food daily.

Contrary to the nutritional needs observed in the wild, much of the information found in lay publications lists fruits and vegetables as a major portion of the captive diet. Fruit-based diets are harmful to captive sugar gliders because they provide inadequate protein and calcium and predispose animals to osteoporosis and periodontal disease.^3,²² Although sugar gliders readily accept fruits, nuts, and grains, these are not a substantial part of their natural diet.

Leadbeater’s diet has been recommended as a base mixture for many sugar glider diets. This is an artificial nectar mix originally formulated for Leadbeater’s possums (Gymnobelideus leadbeateri).^3,^13,¹⁶ Leadbeater’s recipe consists of 150 mL water, 150 mL honey, 1 shelled hard-boiled egg, 25-g high-protein baby cereal, and 1 teaspoon vitamin and mineral powder. This mixture is kept refrigerated until served, with unused refrigerated portions discarded after 2 to 3 days. The mixture can be kept longer if frozen. The original Leadbeater’s recipe is often modified, with adjustments usually being made for palatability rather than nutritional content. Several modified versions are found on the Internet, such as Boubon’s Modified Leadbeater’s Diet and the High Protein Wombaroo Diet (Wombaroo, Adelaide, SA, Australia). These diets should be scrutinized closely, because none of them have undergone thorough nutritional dietary trials and analysis.

Several diets recommended by the authors are listed in Table 29-2. Choose one of these recipes and use it in its entirety. Chop the pieces together so that the gliders cannot pick out only their favorite items. No one commercial diet seems adequate, but long-term nutritional studies are still pending.³

Table 29-2 Suggested Sugar Glider Diets