Keystone Species: The Cassowary

I remember seeing a documentary years ago on the cassowary, and never forgot its significance. Here is some information about why the Cassowary is a keystone species. We have to adapt so that other species survive. Adaptation requires us to change the way we live. It is intelligent to change and exciting also. I am about to go off and live in a tent. If I can do it, others can. Can’t wait, maybe I see a Cassowary.

Cassowaries are Gondwanan in origin and were concentrated in the small part of the supercontinent that later broke apart and became the present areas of Northern Australia, Papua New Guinea and some of the eastern island groups of Indonesia. Two separate populations of Australian cassowary exist – one in the Wet Tropics area from Mt Halifax/Paluma through to Cooktown and the other on Cape York Peninsula in the McIlwraith and Iron Ranges, Jardine River area and the Eastern Dunes. The Australian cassowary is called the Southern Cassowary or sometimes the Double-wattled Cassowary. Once you realise that this species is also found in Papua New Guinea along with two more species and several subspecies, then it becomes clear why ours is called the Southern Cassowary.

A subadult ready to find its own homerange.A cassowary is a solitary animal and when it is a sub-adult, it is banished from the home range of its father. The young animal wanders off to find its own future patch of habitat. It finds a part of the forest where there are no adult cassowaries and starts learning its way around. This is a vulnerable time for the maturing cassowary. Dogs can easily chase it down and kill it; an adult cassowary already resident in that forest can attack it and perhaps the young cassowary may not be able to find sufficient food in a foreign area where it is disoriented.

Once the cassowary has established its home range, it moves regularly through that range which can be quite large. Some of the Daintree animals have a home range of roughly 7 square km. The shape and area of the range changes depending on food and the annual breeding season (courting starts in May/June). Home ranges are not necessarily clearly defined and defended territories – they can overlap. Females tend to have overlapping ranges with several males. On the Tablelands where the habitat is mainly rainforest, the ranges are larger. This increased range leads to fewer interactions between birds.

Cassowary EggsThe female cassowary has turned the tables on what is mostly a maternal social structure in the animal world. The males incubate the eggs and raise the chicks. Once a clutch of eggs is laid, the female will seek out other males with which to mate. For each male that she finds, she will provide a clutch of eggs (usually 3 to 5) for him to nurture.

Why Cassowaries Are So Important

Rainforests would be a very different place with diminished diversity if there were no cassowaries. These huge birds are the only animals capable of distributing the seeds of more than 70 species of trees whose fruit is too large for any other forest dwelling animal to eat and relocate. If these trees did not have an animal to disperse their seeds, they would only occur in concentrated pockets around the parent tree or in places where the seeds rolled such as gullies or the bottom of slopes. As a result over a long period of time the structure of large tracts of forest might change. In tropical rainforests in other parts of the world there are a wide range of animals which fulfill this role. In the Wet Tropics the cassowary plays the role which is accomplished by entire guilds of animals elsewhere.

There are at least another 80 species of plants which are also assisted by the cassowary’s eating habits. These species have smaller seeds but many are toxic and only the cassowary can safely consume them. Such dangerous eating habits are possible because the cassowary has a short/rapid digestive system which appears to be supported by an overactive liver and an unusual combination of stomach enzymes. Other animals such as White-tailed Rats may help distribute these smaller seeds but more often than not, they damage the seed rather than dispersing it intact. So the cassowary is vital for the widespread continuance of over 150 species of plants. That is why the cassowary is referred to as a “keystone species”.

Threats to Cassowaries

The latest estimates suggest the total Australian population of the southern cassowary numbers only between 1,200 and 1,500 adults. Some of the many problems facing cassowaries are:

* loss of habitat through clearing for residential settlement and agricultural expansion,
* fragmented habitat (especially from roads and subdivisions),
* vehicle traffic (road kills are the number one cause of adult cassowary deaths),
* dogs (which are especially aggressive to chicks and juveniles), and
* feral pigs (impact on their habitat).
* Additionally, some birds have been shot although this is illegal.

One of the most ironic threats to cassowaries is the perceived kindness of people who enjoy handfeeding these impressive animals. Once a cassowary is ‘tamed’ and approaches people rather than avoids them, its chances of being killed increase dramatically. This is because the cassowary frequently approaches cars or wanders regularly through residential suburbs where it can be attacked by dogs, especially those breeds kept for their hunting skills.

Cassowary Chicks

There are three specific areas in the Wet Tropics that are ‘hot spots’ for cassowaries: the Daintree area which has the problem of roads cutting through the bird’s home ranges; the Kuranda and Atherton Tableland area which has the problems of habitat loss, fragmentation by roads and marauding dogs; and the Mission Beach area which has suffered extensive habitat loss to the degree that the birds have been squeezed into unnaturally small home ranges. They are forced to seek food from plantation sources and this closeness to human settlements brings them into more frequent contact with dogs. As they try to move around the remaining patches of habitat between the beach and the sloping hinterland behind it, they are commonly run over by cars.

As an endangered and nationally listed species, there is help being directed towards protection and hopefully recovery of cassowary numbers but there is still much that needs to be done. The concern and action of everyone who resides in the Wet Tropics area is needed to save this bird but there are still too many people who aren’t sufficiently interested. Simple steps can go a long way such as slowing down in cassowary ‘hot spot’ areas and keeping dogs restricted to a fenced yard or on a leash.

For information about cassowaries see the Australian Government page about the endangered Southern Cassowary.