The oldest wild koala recorded by Friends of the Koala was a female over 18 years old. Generally, their lifespan is 8 to 15 years. Koalas are aged by assessing the condition of their teeth.
Northern Rivers’ koalas are similar in appearance and size to Queensland koalas. They have a short, thick, grey coat and are smaller than their southern counterparts. A male koala’s average weight is 7- 8kg and a female’s 6-7kg. That is a bit bigger than a basketball when they are curled up in a tree.
Across the region, koalas mate throughout the year, but the mating season peaks between May and September.
Koalas are the size of a small jelly bean when born; their eyes are shut, ears stuck to their head and they have no fur. They take a precarious journey, crawling into their mother’s pouch and attaching themselves to one of their mother’s two teats. Koala joeys spend 6-8 months in their mother’s pouch, and during this time grow fur and their eyes open. From 9-12 months they spend their days on their mum’s tummy, back or close by, learning how to navigate the treetops and adjusting to a diet of eucalyptus leaves. The next few months are spent in the same vicinity as their mother as they become fully independent and weaned. Females often stay in in the same area as their mothers, but young males usually disperse.
The koala’s breeding cycle [344KB]
(source: Bill Phillips. Aust Govt. Publishing Service. 1990.)
Koalas survive mainly on a diet of eucalyptus leaves but they do not eat all species of eucalyptus. Their preferred trees in the Northern Rivers are Forest Red Gum, Tallowwood and Swamp Mahogany although they eat many other eucalypts as well. The trees koalas prefer to eat and use for shelter depend on the particular area and its surrounding habitat. For the Northern Rivers, non-eucalypts such as Paperbarks and She Oaks are often used. A koala’s metabolism is finely balanced between nutritional needs and energy requirements. Habitat disturbance upsets the balance because koalas must range further afield for their food.
Why does a koala choose a particular tree in the forest to feed on? Awareness of the extreme fussiness of the koala in its choice of food dates from the time a koala was first taken into captivity in 1803. Failure of early attempts to exhibit koalas overseas where Eucalyptus foliage was not available and the mortality of many koalas in zoos even in Australia in the early 1900’s reinforced this view. Observations of feeding patterns of koalas in captivity showed that their diet changed at certain times of the year when animals rejected certain species of eucalypt that they showed a strong preference for in other seasons. These same habits have also been observed in the wild.
Field studies seem to indicate that koalas’ tree preference is influenced by their social organization, the structure of the tree and the chemistry of the leaves. Observed differences in tree species preference between sexes, and the preference for individual trees within species, may have their basis in the social organization of the koala. Although adult koalas are rarely seen in the same tree and appear to avoid one another, they nevertheless form clusters in which the home range of the dominant male and several females overlap extensively. Frequent use of a small number of trees by these koalas may provide a means of communication thus maintaining the cohesion of the cluster. Another theory is that the frequent cropping of the tree results in many new shoots being produced, which in turn attracts koalas.
The only structural features of trees that seem to attract koalas according to scientists are tree girth and height. Obviously the bigger the tree, the more food available and therefore the need to move between trees is reduced. This then reduces the energy expended by the koala and also reduces the chance of predation.
The preference for a narrow range of species within the huge Eucalyptus genus appears to have its basis in the chemistry of the leaves. Attempts to identify this basis have focused on either the nutritional or the toxic qualities of the foliage, and for various reasons no real basis has been identified.
Some clues as to why they choose one tree over another may be gleaned by studying the animals in their natural environment. Koalas first sample leaves while riding on their mothers’ backs and so become familiar with the foliage of the trees used by their mothers, but whether this influences their later choice of species has not yet been determined. Koalas frequently draw a branch of leaves to the vicinity of the nose before rejecting or accepting foliage. This will occur in a tree of a preferred species as well as when they are confronted by foliage from different species in captivity. This behaviour suggests that preferred browse food is identified by smell, however what they are actually smelling still remains a mystery.
Eucalypt foliage is considered a poor source of nutrients. It has been estimated that the entire amount of food eaten by a koala in a day (between 500grams and 1 kilogram of eucalypt leaf) contains about the same energy as a bowl of Cornflakes! No wonder the animals sit in the tree seemingly sleeping all day – they don’t have any energy to do anything else. The Eucalypt species favoured by koalas are those often found on fertile soils suggesting that nutrient quality may be an ultimate factor in species preference. The preferred species also tend to be associated with drainage lines or shallow water tables – an important factor in times of drought and at other times encouraging the growth of new tips which have been shown to be richer in nutrients than older leaves.
All in all, mystery still surrounds the whole issue.
For further information, please contact Mark Wilson (Nursery Manager) at firstname.lastname@example.org or phone 0413 339 554.
Koalas are known to live in an area by:
- scratch marks on tree trunks
- scats on the ground
- calls or sounds – video of a male koala grunting
- watch out for all the signs of koala activity and report sightings to us so accurate records of activity and sightings can be maintained.
Male koalas are larger than females and their genitals are visible. They have a longer, broader face and as adults are more muscular. At sexual maturity (2 -3 years) they develop a scent gland on their chest which looks like a dirty, vertical mark down the middle of their upper chest.
Females are smaller, with fluffier ears. They have a rounder, softer face and are less robust.
Koalas are widely distributed across the Northern Rivers of New South Wales although their numbers vary depending on available habitat. There are regular sightings in all the local government areas of Ballina, sightings in all the local government areas of Ballina, Byron, Kyogle, Lismore, Richmond Valley and Tweed. Koalas are found in in areas with extensive bushland such as Horseshoe Creek, Bonalbo, the Border Ranges, Goonengerry, Myocum, Larnook and the Blackwall Range. They also survive in urban areas.areas.
Koalas are known to use people’s yards and even the streets of some towns and villages. Such sightings occur in Byron Bay, Kyogle, Clunes, Dunoon, Federal, Pottsville and Wyrallah, to name a few. In most parts of urban Lismore koalas are commonplace, however there are concerns that koala numbers have decreased in recent times as habitat has been greatly reduced and that which remains is fragmented.