Sugar glider
The sugar glider  (Petaurus breviceps) is a small, omnivorous, arboreal, and nocturnal gliding possum belonging to the marsupial infraclass. The common name refers to its preference for sugary foods such as sap and nectar and its ability to glide through the air, much like a flying squirrel. They have very similar habits and appearance to the flying squirrel, despite not being closely related—an example of convergent evolution. The scientific name, Petaurus breviceps, translates from Latin as "short-headed rope-dancer", a reference to their canopy acrobatics.

The sugar glider is characterised by its gliding membrane, known as the patagium, which extends from its forelegs to its hindlegs, one on each side of its body.  Gliding serves as an efficient means of reaching food and evading predators. The animal is covered in soft, pale grey to light brown fur  which is countershaded, being lighter in colour on its underside.
 
The sugar glider is endemic to parts of mainland Australia, New Guinea and certain Indonesian islands; and it was introduced to Tasmania, probably in the 1830s. It is a popular exotic pet but is prohibited in some regions, including parts of Australia and the United States.

Names
It is known as aymows or kajben in the Kalam language of Papua New Guinea, or yegang in the Asai Valley dialect of Kalam.  Kunwinjku of western Arnhem Land call this animal Lumbalk.

Taxonomy
The genus Petaurus is believed to have originated during the early to mid Miocene period (18 to 24 million years ago), then dispersed from New Guinea to Australia where Australian Petaurus species diverged. The earliest Petaurus species occurred in Australia 4.46 million years ago; and the sugar glider is the only Petaurus species endemic to both Australia and New Guinea.

The species is divided into seven subspecies; three occur in Australia, four in New Guinea, although debate regarding current species delineation continues. These seven subspecies are currently designated by small morphological differences such as colour and body size.  However, genetic analysis using mitochondrial DNA indicates that the morphological subspecies may not represent genetically unique populations.

Contrary to the current geographic distribution of sugar gliders, two genetically distinct populations in Australia may have arisen due to long term geographical isolation following drying of the Australian continent after the Pliocene and the uplift of the Great Dividing Range,  by a process known as allopatric speciation.  One population is found in coastal New South Wales and southern Queensland; and the other is found in northern Queensland, inland and southern New South Wales, Victoria and South Australia.

Further evidence is required to clarify if changes to the current taxonomic divisions are warranted; for example, subspecies P. b. biacensis is provisionally considered a separate species, Biak glider (Petaurus biacensis).

Distribution and habitat

Sugar gliders are found throughout the northern and eastern parts of mainland Australia, Tasmania, New Guinea and several associated isles, the Bismarck Archipelago, Louisiade Archipelago, and certain isles of Indonesia, Halmahera Islands of the North Moluccas. The earliest Australian sugar glider fossils were found in a cave in Victoria and are dated to 15,000 years ago, at the time of the Pleistocene epoch. The facilitated introduction of the sugar glider to Tasmania in 1835 is supported by the absence of skeletal remains in subfossil bone deposits and the lack of an Aboriginal Tasmanian name for the animal. In Australia, sugar glider distribution corresponds with forests along the southern, eastern and northern coastlines, and extends to altitudes of 2000 m in the eastern ranges.

The sugar glider occurs in sympatry with the squirrel glider, mahogany glider, and yellow-bellied glider; and their coexistence is permitted through niche partitioning where each species has different patterns of resource use.

They have a broad habitat niche, inhabiting rainforests and coconut plantations in New Guinea; and rainforests, wet or dry sclerophyll forest and acacia scrub in Australia; preferring habitats with Eucalypt and Acacia species. The main structural habitat requirements are a large number of stems within the canopy, and dense mid and upper canopy cover, likely to enable efficient movement through the canopy.

Like all arboreal, nocturnal marsupials, sugar gliders are active at night, and they shelter during the day in tree hollows lined with leafy twigs.
 
The average home range of sugar gliders is , and is largely related to the abundance of food sources; density ranges from two to six individuals per hectare (0.8–2.4 per acre).

Native owls (Ninox sp.) are their primary predators; others in their range include kookaburras, goannas, snakes, and quolls. Feral cats (Felis catus) also represent a significant threat.

Appearance and anatomy

The sugar glider has a squirrel-like body with a long, partially (weakly) prehensile tail. The length from the nose to the tip of the tail is about , and males and females weigh  respectively. Heart rate range is 200–300 beats per minute, and respiratory rate is 16–40 breaths per minute. The sugar glider is a sexually dimorphic species, with males typically larger than females. Sexual dimorphism has likely evolved due to increased mate competition arising through social group structure; and is more pronounced in regions of higher latitude, where mate competition is greater due to increased food availability.

The fur coat on the sugar glider is thick, soft, and is usually blue-grey; although some have been known to be yellow, tan or (rarely) albino. A black stripe is seen from its nose to midway on its back. Its belly, throat, and chest are cream in colour. Males have four scent glands, located on the forehead, chest, and two paracloacal (associated with, but not part of the cloaca, which is the common opening for the intestinal, urinal and genital tracts) that are used for marking of group members and territory. Scent glands on the head and chest of males appear as bald spots. Females also have a paracloacal scent gland and a scent gland in the pouch, but do not have scent glands on the chest or forehead.

The sugar glider is nocturnal; its large eyes help it to see at night and its ears swivel to help locate prey in the dark. The eyes are set far apart, allowing more precise triangulation from launching to landing locations while gliding.

Each foot on the sugar glider has five digits, with an opposable toe on each hind foot. These opposable toes are clawless, and bend such that they can touch all the other digits, like a human thumb, allowing it to firmly grasp branches. The second and third digits of the hind foot are partially syndactylous (fused together), forming a grooming comb. The fourth digit of the forefoot is sharp and elongated, aiding in extraction of insects under the bark of trees.

The gliding membrane extends from the outside of the fifth digit of each forefoot to the first digit of each hind foot. When the legs are stretched out, this membrane allows the sugar glider to glide a considerable distance. The membrane is supported by well developed tibiocarpalis, humerodorsalis and tibioabdominalis muscles, and its movement is controlled by these supporting muscles in conjunction with trunk, limb and tail movement.

Lifespan in the wild is up to 9 years; is typically up to 12 years in captivity, and the maximum reported lifespan is 17.8 years.

Biology and behaviour

Gliding
The sugar glider is one of a number of volplane (gliding) possums in Australia. Gliders glide with the fore- and hind-limbs extended at right angles to their body, with their feet flexed upwards. The animal launches itself from a tree, spreading its limbs to expose the gliding membranes. This creates an aerofoil enabling them to glide  or more. For every  travelled horizontally when gliding, sugar gliders fall . Sugar gliders can steer by moving their limbs and adjusting the tension of their gliding membrane; for example, to turn left, a sugar glider will lower its left forearm below its right.

This form of arboreal locomotion is typically used to travel from tree to tree; the species rarely descends to the ground. Gliding provides three dimensional avoidance of arboreal predators, and minimal contact with ground dwelling predators; as well as possible benefits in decreasing time and energy consumption spent foraging for nutrient poor foods that are irregularly distributed.  Young carried in the pouch of females are protected from landing forces by the septum that separates them within the pouch.

Torpor
Sugar gliders can tolerate ambient air temperatures of up to  through behavioural strategies such as licking their coat and exposing the wet area, as well as drinking small quantities of water.
In cold weather, sugar gliders will huddle together to avoid heat loss, and will enter torpor to conserve energy. Huddling as an energy conserving mechanism is not as efficient as torpor. Before entering torpor, a sugar glider will reduce activity and body temperature normally in order to lower energy expenditure and avoid torpor. With energetic constraints, the sugar glider will enter into daily torpor for 2–23 hours while in rest phase. 
Torpor differs from hibernation in that torpor is usually a short-term daily cycle.  Entering torpor saves energy for the animal by allowing its body temperature to fall to a minimum of  to . When food is scarce, as in winter, heat production is lowered in order to reduce energy expenditure. With low energy and heat production, it is important for the sugar glider to peak its body mass by fat content in the autumn (May/June) in order to survive the following cold season. In the wild, sugar gliders enter into daily torpor more often than sugar gliders in captivity. The use of torpor is most frequent during winter, likely in response to low ambient temperature, rainfall, and seasonal fluctuation in food sources.

Diet and nutrition
Sugar gliders are seasonally adaptive omnivores with a wide variety of foods in their diet, and mainly forage in the lower layers of the forest canopy. Sugar gliders may obtain up to half their daily water intake through drinking rainwater, with the remainder obtained through water held in its food. In summer they are primarily insectivorous, and in the winter when insects (and other arthropods) are scarce, they are mostly exudativorous (feeding on acacia gum, eucalyptus sap, manna, honeydew or lerp). Sugar gliders have an enlarged caecum to assist in digestion of complex carbohydrates obtained from gum and sap.
 
To obtain sap or gum from plants, sugar gliders will strip the bark off trees or open bore holes with their teeth to access stored liquid. Little time is spent foraging for insects, as it is an energetically expensive process, and sugar gliders will wait until insects fly into their habitat, or stop to feed on flowers.
Gliders consume approximately 11 g of dry food matter per day. This equates to roughly 8% and 9.5% of body weight for males and females, respectively.

They are opportunistic feeders and can be carnivorous, preying mostly on lizards and small birds.  They eat many other foods when available, such as nectar, acacia seeds, bird eggs, pollen, fungi and native fruits. Pollen can make up a large portion of their diet, therefore sugar gliders are likely to be important pollinators of Banksia species.

Reproduction

Like most marsupials, female sugar gliders have two ovaries and two uteri; they are polyestrous, meaning they can go into heat several times a year. The female has a marsupium (pouch) in the middle of her abdomen to carry offspring. The pouch opens anteriorly, and two lateral pockets extend posteriorly when young are present. Four nipples are usually present in the pouch, although reports of individuals with two nipples have been recorded. Male sugar gliders have a bifurcated penis to correspond with the two uteri of females.

The age of sexual maturity in sugar gliders varies slightly between the males and females. Males reach maturity at 4 to 12 months of age, while females require from 8 to 12 months. In the wild, sugar gliders breed once or twice a year depending on the climate and habitat conditions, while they can breed multiple times a year in captivity as a result of consistent living conditions and proper diet.

A sugar glider female gives birth to one (19%) or two (81%) babies (joeys) per litter. The gestation period is 15 to 17 days, after which the tiny joey  will crawl into a mother's pouch for further development. They are born largely undeveloped and furless, with only the sense of smell being developed.  The mother has a scent gland in the external marsupium to attract the sightless joeys from the uterus.  Joeys have a continuous arch of cartilage in their shoulder girdle which disappears soon after birth; this supports the forelimbs, assisting the climb into the pouch. Young are completely contained in the pouch for 60 days after birth, wherein mammae provide nourishment during the remainder of development.  Eyes first open around 80 days after birth, and young will leave the nest around 110 days after birth. By the time young are weaned, the thermoregulatory system is developed, and in conjunction with a large body size and thicker fur, they are able to regulate their own body temperature.

Breeding is seasonal in southeast Australia, with young only born in winter and spring (June to November). Further north in Arnhem Land, breeding is not seasonally restricted and young may be born throughout the year.
Unlike animals that move along the ground, the sugar glider and other gliding species produce fewer, but heavier, offspring per litter.  This allows female sugar gliders to retain the ability to glide when pregnant.

Socialisation
Sugar gliders are highly social animals. They live in family groups or colonies consisting of up to seven adults, plus the current season's young. Up to four age classes may exist within each group, although some sugar gliders are solitary, not belonging to a group. They engage in social grooming, which in addition to improving hygiene and health, helps bond the colony and establish group identity.

Within social communities, there are two codominant males who suppress subordinate males, but show no aggression towards each other. These co-dominant pairs are more related to each other than to subordinates within the group; and share food, nests, mates, and responsibility for scent marking of community members and territories.

Territory and members of the group are marked with saliva and a scent produced by separate glands on the forehead and chest of male gliders. Intruders who lack the appropriate scent marking are expelled violently. Rank is established through scent marking; and fighting does not occur within groups, but does occur when communities come into contact with each other. Within the colony, no fighting typically takes place beyond threatening behaviour. Each colony defends a territory of about  where eucalyptus trees provide a staple food source.

Sugar gliders are one of the few species of mammals that exhibit male parental care. The oldest codominant male in a social community shows a high level of parental care, as he is the probable father of any offspring due to his social status.
This paternal care evolved in sugar gliders as young are more likely to survive when parental investment is provided by both parents. In the sugar glider, biparental care allows one adult to huddle with the young and prevent hypothermia while the other parent is out foraging, as young sugar gliders aren't able to thermoregulate until they are 100 days old (3.5 months).

Communication in sugar gliders is achieved through vocalisations, visual signals and complex chemical odours. Chemical odours account for a large part of communication in sugar gliders, similar to many other nocturnal animals. Odours may be used to mark territory, convey health status of an individual, and mark rank of community members. Gliders produce a number of vocalisations including barking and hissing.

Human relations

Conservation 
The sugar glider is not considered endangered, and its conservation rank is "Least Concern (LC)" on the IUCN Red List. Despite the loss of natural habitat in Australia over the last 200 years, it is adaptable and capable of living in small patches of remnant bush, particularly if it does not have to cross large expanses of cleared land to reach them. However, several close relatives are endangered, particularly Leadbeater's possum and the mahogany glider. Sugar gliders may persist in areas that have undergone mild-moderate selective logging, as long as three to five hollow bearing trees are retained per hectare. Although not currently threatened by habitat loss, the ability of sugar gliders to forage and avoid predators successfully may be decreased in areas of high light pollution.

Conservation in Australia is enacted at the federal, state and local levels, where sugar gliders are protected as a native species. The central conservation law in Australia is the Environment Protection and Biodiversity Conservation Act 1999 (EPBC Act). The National Parks and Wildlife Act 1974 is an example of conservation law in the state of South Australia, where it is legal to keep (only) one sugar glider without a permit, provided it was acquired legally from a source with a permit. A permit is required to obtain or possess more than one glider, or if one wants to sell or give away any glider in their possession. It is illegal to capture or sell wild sugar gliders without a permit.

Introduction to Tasmania

According to naturalist Ronald Campbell Gunn, no Petaurus species is indigenous to Tasmania. He concluded that sugar gliders had been brought to Launceston, Tasmania as pets from Port Phillip, Australia (now Melbourne) soon after the founding of the port in 1834.  Some sugar gliders had escaped and quickly became established in the area. The species has been identified as a threat to the survival of the swift parrot, which breeds only in Tasmania. Reduction in mature forest cover has left swift parrot nests highly vulnerable to predation by sugar gliders, and it is estimated that the parrot could be extinct by 2031.

In captivity

In captivity, the sugar glider can suffer from calcium deficiencies if not fed an adequate diet. A lack of calcium in the diet causes the body to leach calcium from the bones, with the hind legs first to show noticeable dysfunction. Calcium to phosphorus ratios should be 2:1 to prevent hypocalcemia, sometimes known as hind leg paralysis (HLP). Their diet should be 50% insects (gut-loaded) or other sources of protein, 25% fruit and 25% vegetables. Some of the more recognised diets are Bourbon's Modified Leadbeaters (BML), High Protein Wombaroo (HPW) and various calcium rich diets with Leadbeaters Mixture (LBM).  Iron storage disease (hemochromatosis) is another dietary problem that has been reported in captive gliders and can lead to fatal complications if not diagnosed and treated early.

Plenty of attention and environmental enrichment may be required for this highly social species, especially for those kept as individuals. Inadequate social interaction can lead to depression and behavioural disorders such as loss of appetite, irritability and self-mutilation.

As a pet 

In several countries, the sugar glider is popular as an exotic pet, and is sometimes referred to as a pocket pet. In Australia, there is opposition to keeping native animals as pets from Australia's largest wildlife rehabilitation  organisation (WIRES), and concerns from Australian wildlife conservation organisations regarding animal welfare risks including neglect, cruelty and abandonment.

In Australia, sugar gliders can be kept in Victoria, South Australia, and the Northern Territory. However, they are not allowed to be kept as pets in Western Australia, New South Wales, the Australian Capital Territory, Queensland or Tasmania.

Sugar gliders are popular as pets in the United States, where they are bred in large numbers. Most states and cities allow sugar gliders as pets, with some exceptions, including California, Hawaii, Alaska, and New York City. In 2014, Massachusetts changed its law, allowing sugar gliders to be kept as pets.<ref>{{cite web|last=MacCallum|first=Wayne F. , Director|title=Notice of Changes In the Law Relative to Wildlife that May be Sold By Licensed Pet Shops or Kept as Pets in Massachusetts|url=http://www.mass.gov/eea/docs/agr/animal-health/pet-shop-licensing/new-requirements-for-exotic-animals-sold-in-pet-shops.pdf|work=Division of Fisheries & Wildlife|publisher=Commonwealth of Massachusetts|accessdate=10 February 2014}}</ref> Some other states require permits or licensing.  Breeders of sugar gliders are regulated and licensed by the US Department of Agriculture (USDA) Animal and Plant Health Inspection Service (APHIS) through the Animal Welfare Act.

It has been suggested that the expanding overseas trade in sugar gliders was initiated from illegally sourced sugar gliders from Australia, which were bred for resale in Indonesia. DNA analysis, however, indicates that "the USA sugar glider population originates from West Papua, Indonesia with no illegal harvesting from other native areas such as Papua New Guinea or Australia". There have been numerous media and internet articles which evidence a history of cruelty. There are also many internet and media articles reporting on why sugar gliders should not be kept as pets.  Sugar glider rescue organisations have been set up in several US States to cope with surrendered and abandoned sugar gliders.

Notes
 Species notes 

 Footnotes