Cassowaries, the threatened 'gardeners of the rainforest'

Australian Cassowary, Casuarius casuarius. Photo by Hans and Judy Beste

The Southern Cassowary is an iconic bird of Australia's north. Its large size and spectacular appearance make it easily recognisable. It also plays a key role in rainforest ecology, eating fruits that are too large for most other animals to digest and dispersing their seeds over long distances.  Most seeds are still viable after digestion and over 238 plant species have been recorded in Cassowary diets, making the birds very important for maintaining the long term health of rainforests. This role that Cassowaries play in dispersing seeds is a good example of one of the key ecological processes that the WildCountry Science Council have defined as being critical to securing long term health of Australia's landscapes.

Cassowaries are large, with heights of up to two metres and females weighing as much as 76kg. They are very distinctive, with black plumage, a blue face and neck with red wattles, a large beak and a helmet-like casque on their heads. They also have heavy legs and sharp dagger-like toes.

In spite of individuals having a tough appearance and a generally long life span, this distinctive bird is in decline. It is uncertain how many individuals remain but estimates of the population size in the Wet Tropics went from 2500-4000 adults in 1988 to less than 1500 in 2001. The other main population, on Cape York Peninsula is also thought to be in decline.

Take action!

Visit savethecassowary.org.au to send an email to Minister Garrett asking for his assistance.

There are several factors that are likely to be leading to the reduction of Cassowary populations. First and foremost is the loss and fragmentation of their rainforest habitat. The birds require dense tropical rainforest for feeding, nesting and shelter. Other habitat types are used and Cassowaries will cross some gaps between patches but they do require some large areas of high quality core habitat. They also need access to permanent fresh water and are frequently found in flat, swampy areas.  The birds' large size means that to find enough food they require large areas of intact rainforest. Their diet changes seasonally as the fruit of different plants becomes available and they move throughout their range to find this food.  Loss of habitat restricts the numbers of birds that can be supported by the remaining forest, while its fragmentation increases the distance that birds must travel to find food. It also increases the dangers they are subject to during their travels. The main cause of this habitat loss and fragmentation is land development for housing.

Land development also brings other dangers to cassowaries. Amongst these dangers are roads.  Cassowaries that are accustomed to roaming free across large areas of intact forest are very vulnerable to being hit by cars on the roads that increasingly divide their ranges.  During 2001, 28 cassowaries were known to be killed on roads around Mission Beach.  This was 76% of the known deaths in the local population during that year.  Roads also bring more long term damage, introducing weeds, reducing habitat quality along their margins, increasing the chance of bushfires and being the precursor to further development. Domestic and wild dogs are another source of threat, mainly to chicks and sub-adults. The extirpation (complete loss) of some subpopulations may have been caused in part by predation by dogs. As reproductive rates are low, the loss of juvenile birds can take a long time to recover.

Cassowaries already face challenges from natural disturbances such as bushfires and cyclones. The further fragmentation and degradation of their habitat as well as increased mortality due to land development compounds these challenges and makes recovery more difficult. The long term health of subpopulations also suffers if they become too small and isolated, with insufficient numbers of birds interbreeding. Maintenance of evolutionary processes is another of the key ecological principles defined by the WildCountry Science Council - it seems that for Cassowaries, this requires the conservation or restoration of large areas of good habitat, allowing communication between the groups that are currently isolated by forest clearing. While much of the remaining Cassowary habitat is now protected, over 80% of all habitats in the coastal lowlands of the Wet Tropics had already been cleared.  This means that all remaining habitat is of great importance.  A Commonwealth government recovery plan has already outlined some measures to help conserve the Cassowary in its natural environment.  A new campaign, 'Save the Cassowary' is asking the government to assist in protecting the rest of the core habitat currently on private land by providing funds for essential land purchases and incentive schemes for private landowners at locations such as Mission Beach.

Take action!

Visit savethecassowary.org.au to send an email to Minister Garrett asking for his assistance.

Without this kind of action to protect intact areas of core rainforest habitat it is likely that further land development together with existing threats will bring us closer to losing these spectacular 'rainforest gardeners of the north'.

Sources:

Department of Environment and Resource Management, 2009 'Cassowary'  http://www.derm.qld.gov.au/wildlife-ecosystems/wildlife/threatened_plants_and_animals/endangered/cassowary.html#conservation_status Accessed 7 June 2010

Department of the Environment, Water, Heritage and the Arts (2010). Casuarius casuarius johnsonii in Species Profile and Threats Database, Department of the Environment, Water, Heritage and the Arts, Canberra. Available from: http://www.environment.gov.au/sprat Accessed Friday, 4 Jun 2010

Latch, P. 2007. National recovery plan for the southern cassowary Casuarius casuarius johnsonii . Report to Department of the Environment, Water, Heritage and the Arts, Canberra. Environmental Protection Agency.