Birds - The Cassowary
corporate logo of the Wet Tropics Management Authority features
a relic plant, the cycad Bowenia spectabilis, and
a relic animal - the Southern cassowary (Casuarius casuarius
johnsonii). This colourful creature with its brilliant blue
and purple head and neck and red wattles appears extensively in
promotional brochures throughout the region. However, it is an endangered
species and its future is uncertain.
In evolutionary terms, the flightless birds, or
ratites, were some of the earliest types of birds to develop. Some
still exist today including the emu, rheas, kiwis and the ostrich.
But several have become extinct in recent times including the Moas
of New Zealand and the Elephant Bird of Madagascar. Some of these
primitive birds are recognised as such because they have feathers
which are not structured for aerodynamic flight. One of the most
striking features about the cassowary is its long and unusual black
feathers. Cassowary feathers differ from other birds in that they
have a quill that splits in two.
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.
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
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 nuture.
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.
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.
If the whole community takes up the challenge,
we could save the cassowary.