Saturday, 31 January 2009
Cassowary dung and DNA
There have been a number of articles this week on using DNA sampling of faeces from the Southern Cassowary to project population levels in Queensland, Australia.
Unfortunately these days one is never quite sure how much media hype is involved and how much factual reporting is substituted by sensationalism.
The Southern or Australian Cassowary, Casuarius casuarius johnstonii, is an endangered species. At the time of the first European settlements in the early 19th Century, the cassowary lived in the tropical rainforests which stretched for over 600km from the Paluma Range, north of Townsville, to the tip of Cape York and probably had a population in excess of 10,000.
It is now only to be found in two rainforest segments, the Mission Beach and Daintree areas, representing perhaps 20% of the original habitat.
At the last estimate its numbers were assessed as between 1,200 and 1,500. In the meantime tropical storms, like Larry, have certainly had an impact and road-kills are continuously impacting (no pun intended) on the population. A new survey to establish population numbers would certainly be useful.
Using modern technology to extract DNA samples from faeces is possible and would establish which individual had deposited it. The Cassowary is an extremely shy bird under normal circumstances and any population survey must rely on indirect observation rather than a head count. Faeces are evidence of a bird’s presence, but in themselves only indicate temporal passage (again no pun intended) of a bird. The main advantage of using this technique would be to specifically identify the Cassowary in question and perhaps thereby map the home range and indicate the breeding potential. Although hunger, as evidenced after tropical storm Larry and other similar disasters, will cause Cassowaries to migrate, normally these birds inhabit well delineated ranges which are strongly contested. Once these ranges have been established it is, except for offspring in the male ranges, very unlikely that other Cassowaries will be found in them, except as transients. Young adults do migrate looking to found their own range and depending on the availability of suitable forest will travel great distances to find them.
For any attempt at wildlife conservation, accurate information is an essential prerequisite for the ultimate success of a project. Certainly the proposed DNA sampling is likely to produce useful information about which Cassowaries are where, but the required scale of sampling will have to be huge to be meaningful. Traditional methods of extrapolating head counts, local reports allied with faeces observed will need to be intensified and frequently repeated to give a meaningful result and of a suitable accuracy to form the basis of future conservation measures. It seems that some funding has been made available to CSIRO for the project, but the A$ 50,000 recently donated will hardly employ a DNA technician for very long. If CSIRO are serious about DNA sampling it will require some substantial investment over a few years. The Cassowary is worth it, but projects have been trumpeted before and subsequently collapsed due to lack of resources. With hindsight, the Cassowary may benefit more from preventing road kills and stopping human expansion into rainforest habitat than from employing another member of staff at CSIRO to analyse its defecated food remains.