One of Campbelltown Council’s councillors, facing re-election in the upcoming elections, recently suggested that the city should construct a “Big Koala” (BK) in the style of other “big local features” such as the Big Prawn, the Big Merino, and the Big Banana. It would be NSW’s first Big Koala, and if done with panache it could outshine the two Victorian Big Koalas, one at Dadswell Bridge and another at Cowes.
The Campbelltown councillor felt that a BK would focus attention on Campbelltown’s koala population, its bushland perimeter, its newly proclaimed Dharawal National Park, and would stimulate tourism. The new national park was saved from becoming a residential area because of the discovery of koalas there in 1986. Community reaction and the efforts of the councillor and the Macarthur National Parks Association led to the final success in 2012 of preserving the area as a national park.
Is the Campbelltown koala population worthy of a grand and imposing BK structure? Compared to koala populations north of Sydney and in Victoria, it is relatively small and of low density. There are many cities, therefore, that might feel they are more worthy of a BK. It’s difficult, however, to assess numbers of koalas. On a national scale, the estimates range from 50,000 to 1,000,000, a twentyfold difference. It is important to realise that koalas can survive and breed at very low densities. These densities (e.g. 1 per 200 hectares) can be so low that finding koalas is very difficult. Yet there is such a large area of potential habitat that even at 1 per 200 hectares the overall number of koalas can be considerable.
In the Campbelltown koala population, my colleagues and I have found breeding females on the western side of the Georges River from Macquarie Fields to Appin. We guess that 300 koalas occupy this area. However, on the eastern side of the river is the Army’s fenced-in Holsworthy firing range, which connects with Heathcote NP and Royal NP and the catchment of the Woronora reservoir. Koalas live there but at an unknown and probably very low density. Consider also that that area adjoins the protected catchment areas of the Cataract, Avon, Cordeaux, and Nepean Dams. These catchments adjoin Moreton NP which in turn connects with Budawang NP, then Deua NP, Wadbilliga NP and the South-East Forests. The combined, connected area is huge but contains a low density of koalas. However, the total number is likely to be large. The same argument applies to habitat to the north of Sydney which includes the Ku-ring-gai Chase NP, the huge Wollemi NP and Yengo NP. Sadly, these areas are incompletely surveyed.
There is some evidence that low densities may have been the norm in pre-white settlement. Despite widespread clearing of the Sydney basin in the colony’s first years, the first koala was not reported till 1798 - a decade after the First Fleet - in the Bargo area, and the first physical evidence was not obtained till 1802 when the French explorer, Barrallier, swapped two spears and a tomahawk for two koala feet near Nattai. Clearly the koala was much prized to warrant such a price! The first whole specimens were captured in 1803, one probably from Nattai and the other from near Port Kembla. Only the latter is preserved in a museum.
So the early koalas were seen only south of Sydney, from a population which probably included the Campbelltown koalas and was probably of low density. Some researchers consider that koalas could not have been in the Sydney Basin itself at the time of white settlement otherwise they would have been sighted by land clearers. The reason for this absence must be either that the koalas were at an extremely low density brought about by aboriginal hunting and/or dingoes, fire or disease, or that the habitat was unsuitable for koalas. The latter case seems unlikely given that the Basin’s shale soils are more fertile than the shale/sandstone soils that koalas use at Campbelltown. It is generally agreed that the more fertile soils are preferred by koalas. However, it may be that the shale/sandstone transition soils offer a greater choice of food species.
Never the less, predation seems to be the most likely explanation for the absence of koalas in the Sydney Basin. If, for example, there were 2000 hunters in the Basin then each would have to kill only 5 per year to have an annual harvest of 10,000 koalas. The great mammalogist, John Gould, in travelling from Sydney to Brisbane in 1838 never saw a koala except with the help of Aboriginal guides. Gould also noted the skill with which the guides located and captured koalas. However, by 1844 the demise of the Aboriginal population was being associated with increases in koala numbers.
Another significant feature of the Campbelltown koala population is its apparent freedom from chlamydial disease which affects most mainland populations. No clinical signs of the disease have been observed during our 20-year-study but affected animals from the Southern Highlands have recently been discovered, and spread of the disease to Campbelltown is, sadly, inevitable provided the Campbelltown population continues to expand. One positive result which might arise from construction of a BK is that donations to the Wildlife Health and Conservation Centre at Cobbitty run by the University of Sydney’s School of Veterinary Science might increase, thus allowing research on chlamydia in the Southern Highlands to continue.
One of the goals of the BK construction would be to attract tourists who would reasonably expect to see a koala or two in an afternoon’s visit. However, local densities of 1 koala per 20 hectares mean that bushwalkers might expect to see a koala only once every few days. This compares with a density of several koalas per hectare at a tourist site in Victoria where several wild-living koalas could be seen from one vantage spot. Then if chlamydiosis should arrive at Campbelltown, tourists would be even more disappointed because koalas would become even harder to find as the disease took its toll.
On the other hand if more discrete populations suddenly emerge, as Campbelltown’s has since 1986, from that large, southern, low density reservoir of koalas, then other towns may be wanting their own BK.
Comments welcome below.