Sugar Gliders; A Natural History

I can't believe I never posted this on SL!!??

The Sugar gliders (Petaurus breviceps) is the second smallest of the gliders and the smallest of the Petaurid family, and are found in woodlands, eucalypt forests and rainforests of Southern, Eastern and Northern Australia, New Guinea and Indonesia. They are the only Australian glider to inhabit Tasmania although they are not a naturally occurring species; they were introduced to Launceston around 1835, and by 1851 were very well established in that area. Sugar Gliders are also the only Australian glider to inhabit New Guinea and some of its neighbouring islands.

The Sugar Glider is the most widespread of the Glider species, with 7 sub species (3 of which in Australia and 4 are found in New Guinea), each one differing in location and physical traits. Generally, Sugar gliders follow ‘Bergman’s Rule’, which means, the higher the latitude the bigger the glider. The factors that contribute to this are thought to be; the lower temperatures at higher latitudes, which therefore increases the need for greater body weight. Another theory is the longer nights at higher latitudes which allow the nocturnal gliders more time to eat, so they grow larger than their counterparts at lower latitudes.

A Glider colony has a home range of around 6 hectares, with up to 6 individuals per hectare. The core area is the area around den sites, these areas are rarely shared with other colonies. Additionally, the peripheral area is usually inhabited by other colonies; it is a shared area where neighbouring colonies will squabble over feeding sites.

Gliders are arboreal, which means they spend most of their lives in the canopy of the forest, they will occasionally descend to the forest floor but this makes them very vulnerable to ground dwelling predators as well as to aerial predators.

As canopy dwellers, the dens are found high up in tree hollows where they will live in colonies of between 2 and 12 individuals, this is mainly to conserve energy as they huddle together to share body heat. The den entrance is large enough to let only gliders and other smaller animals in, but small enough to keep out predators, it is believed that gliders choose their den site in accordance to the weather, in colder months they will nest in dead trees, the rotting wood produces heat much like a compost heap, and in warmer months they will nest in live trees, the water flowing through the live tissues of the tree keeps them cool and it is also a good source of moisture. Gliders are known to den swap, where one colony will have up to 5 dens in use. There are a number of reasons for this, the main one being the avoidance of predators, by swapping which den they use a predator will not recognize a pattern of emergence. Joeys will often be placed into another den (other than the one currently in use) whilst the adults go out to hunt and feed, they will be left with an adult to make sure they stay warm and do not wander off. Nests are lined with leaves and strips of bark which they will transport to the den in their tails, captive gliders will often display this behaviour if provided with live branches or with strips of shredded paper and sometimes toys.

The den not only provides shelter and a place to rest and sleep during the day, but as protection against predators, as previously mentioned the entrance is too small for larger predatory animals. The main threat to wild gliders are large owls, but everything about a Sugar Glider is about predator avoidance; they are nocturnal, thereby avoiding daytime predators, they have evolved to glide which not only conserves energy but will break a scent trail, they are camouflaged, the body colour is broken up by the black stripe in order for them to blend in with their surroundings. They have an alarm call which sounds like a small dog yapping, when the warning is sounded gliders in the area will remain motionless until the perceived threat goes away, this is called ‘crypsis’. As well as the alarm call, Gliders have a defense vocalization, in captive gliders we call this ‘crabbing’. It is a very loud and unusual sound, if a den is attacked the colony inside will all crab, the crabbing alone is very loud, combined with the echo from the tree hollow this would give the aural appearance of a very large animal, the cacophonic sound alone is probably enough to deter a predator as they have sensitive hearing. If a glider is attacked in the open; they are particularly vulnerable whilst feeding, and have also been knocked to the ground whilst volplaning (gliding), the crabbing will attract other members of the colony. Professor David Lindenmayer observed a group of wild gliders successfully driving a Boobook owl away, so safety in numbers is another important aspect of survival, a lone glider will not live long in the wild.

As well as avoiding predators by den swapping, familiarity of the home range and knowing all the escape routes and den locations is extremely important and can be crucial during a pursuit. The average life expectancy of a wild Sugar Glider is 4-5 years.

The Sugar Glider has evolved physically to a nocturnal life; the eyes are large to capture as much incidence light as possible. They function in the same way as other mammal’s eyes, the only difference is in nocturnal animals, the cells in the eyes called rods are far more sensitive, they are the light receptors. The cones which are responsible for colour vision are less sensitive. A layer of cells in the eye called the tapetum lucidum aids vision by reflecting more of the incidence light to the back of the retina which ensures maximum use of minimum light. It is this layer that causes ‘eyeshine’, which is used for detecting animals at night using a flashlight, the Sugar Glider has very weak eyeshine when compared to other gliders, the eyes glow a pale red.

The gliding membrane is called the patagium, it stretches from front limb to hind limb. Gliders cannot fly and gain altitude, they can only glide downhill. They will move to a highpoint, assess their course, prepare themselves and then launch, a split second later the arms and legs are out stretched extending the patagium and the glider will glide silently to the chosen landing site. The tail acts as a rudder which can alter the direction of the glide slightly, as can the body position, distances of up to 60m can be reached in a single glide, although most jaunts are considerably less, they can also take flying prey whilst gliding. Very sharp claws and the presence of large ridged pads on the hands and feet help the glider grip onto the landing site and they also help the glider to climb tree trunks with ease, but gliders can also descend vertical tree trunks head first just as quickly, this is because the feet are positioned at a 90° angle to the leg to allow them to rotate the foot a further 90° so it is literally facing backwards. On the ground they can move quickly but because of the foot position they tend to hop and skip rather than run.

Have you ever looked at the teeth of a Sugar Glider? The top teeth overhang (which is normal), and the bottom teeth are very long, and dominate the lower jaw, this is known as diprotodonta. The incisors (front teeth) are sharp, long and chisel like; they are used for gouging through the tissues of trees and for stripping bark. The molars (back teeth) are squared off and are designed for compaction, they crunch up insect bodies to extract the nutritious soft inner tissue and discard the outer shell. As well as predator avoidance, gliding allows them to move further afield in the search for food. The diet consists of arthropods (beetles, moths etc), gums, sap, honeydew, manna, nectar, pollen and the occasional bird. Sap and gum feeding takes up approximately half of the gliders feeding time.

Honeydew are surplus sugars excreted by insects, the insects feed on tree sap, they incise a small wound in the trunk and suck up the sap in huge amounts to extract the small amount of protein in the substance. The wound in the tree then becomes blocked by oozing sap and crusts over; this white crusty layer is called manna, another Sugar Glider delicacy.

Sap is taken from eucalyptus trees, the gliders will gouge a hole and ‘drink’ the sap, they frequently change sap sites as the eucalypt trees heal the wound by producing a substance called kino which is inedible.

Gum is taken from acacia trees, the gum is indigestible by most other animals, but the Sugar Glider has an enlarged caecum (part of the intestine) which is believed to aid digestion by fermentation. They will also use acacia and eucalypt trees when in bloom to provide the nectar and pollen in the diet.

Gliders at different latitudes have slightly different diets, for example, Gliders found in Northern Australia use pollen as their main protein source for reproduction. In Victoria arthropods are the main protein source for reproduction. In New Guinea gliders will feed on fruits, lowland pitpit (Saccharum edule) which is a species of sugarcane, and beetle larvae.

They will only emerge from the nest for feeding on clear nights, if the weather is bad they will remain huddled together to conserve energy, Sugar Gliders will exhibit a kind of shallow hibernation called ‘torpor’, this can last for around 13 hours, the body will slow down, the body temperature will drop and their metabolism will slow down.

Sugar Gliders are a marsupial, which means the young are born at a foetal stage and develop further in the mothers pouch. They are polyoestrus, which means they can produce more than one litter a year. The location of the gliders affects the months in which they breed, in the Southern parts for example they breed between the months of November and April, and in the Northern parts between August and November, but whatever location, breeding coincides with an abundance of insects at the time of pouch emergence, this is to provide the mother with extra energy and nutrients required for late lactation.

The gestation period is approximately 16 days, after this time the joey is born and will make its way to the pouch where it stays for between 60-70 days. There are 4 nipples in the pouch but they usually only have 1 or 2 young. In captivity triplets are rare and quadruplets are virtually unheard of. The composition of the milk changes as the joey gets older; each nipple is capable of producing milk with a slightly different composition to cater for joeys of different ages, this enables them to breed in quick succession if the joey is lost.

Joeys remain with the parents until the next breeding season when they are driven away, this is called dispersal. They will venture out on their own to make a new colony with others which have also been dispersed, or if they are very lucky they will be recruited by another colony, but this only happens if they have lost one of their own members. The youngsters are very vulnerable at this time and the mortality rate is high.

Sugar Gliders are probably the most successful and certainly the most widely distributed of the Australian marsupials. Their success is due to their capability to adapt to their surroundings, in captivity we feed them a diet that in no way resembles their natural diet yet they thrive. They are a very popular pet now across the world and prove to be very resilient if provided with the correct environment and adequate nutrition. By learning a little more about their NATURAL history and lifestyle we can improve their life in captivity.

© Shropshire Exotics 19/04/07

Reading material that helped with this post:

Gliders of Australia: A Natural History (David Lindenmayer)
Marsupials (Patricia J. Armati et al)

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