Black Swan
There are variety of birds that is breed and kept in Wildlife Fauna Janda Baik. Here is only some of them.
The Black Swan, Cygnus atratus, is a large waterbird which breeds mainly
in the southeast and southwest regions of Australia. The Black Swan was
formerly placed into a monotypic genus, Chenopis.
'Swan' is the common gender term, but 'cob' for a male and 'pen' for a
female are also used, as is 'cygnet' for the young. Collective nouns include
a 'bank' (on the ground) and a 'wedge' (in flight). Black Swans can be found
singly, or in loose companies numbering into the hundreds or even thousands.
Description
Black Swans are mostly black feathered, with a line of white flight feathers
of the wing edges that sometimes show when at rest, and are conspicuous in
flight. The bill is bright red, with a pale bar and tip; and legs and feet
are greyish-black. Cobs (males) are slightly larger than pens (females),
with a longer and straighter bill. Cygnets (immature birds) are a greyish-brown
with pale-edged feathers. [3]
Profile
A mature Black Swan measures between 1.1 and 1.4 metres in length and weighs
6-9 kg. Its wing span, in flight, is between 1.6 and 2 metres.[3] The neck
is long (relatively the longest neck among the swans) and curved in an "S".
The Black Swan utters a musical and far reaching bugle-like sound, called
either on the water or in flight, as well as a range of softer crooning
notes. It can also whistle, especially when disturbed while breeding and
nesting. [3][4]
The Black Swan is unlike any other Australian bird, although in poor light
and at long range it may be confused with a magpie-goose in flight. However
the Black Swan can be distinguished by its much longer neck and slower wing
beat.[5]
Distribution
The species has a large range, with figures between one to ten million km²
given as the extent of occurrence. The current global population of the
Black Swan is estimated to be up to 500,000 individuals. No threat of
extinction, or significant decline in population has been identified in this
numerous and widespread bird. [6]
The Black Swan is common in the wetlands of south western and eastern
Australia and adjacent coastal islands. In the south west the range
ecompasses an area between North West Cape, Cape Leeuwin and Eucla; while in
the east it covers are large region bounded by the Atherton Tableland, the
Eyre Peninsula and Tasmania, with the Murray Darling Basin supporting very
large populations of Black Swans. [3][7] It is uncommon in central and
northern Australia.
The Black Swan's preferred habitat extends across fresh, brackish and salt
water lakes, swamps and rivers with underwater and emergent vegetation for
food and nesting materials. Permanent wetlands are preferred, including
ornamental lakes, but Black Swans can also be found in flooded pastures and
tidal mudflats, and occasionally on the open sea near islands or the shore.
[3]
Black Swans were once thought to be sedentary, but the species is now known
to be highly nomadic. There is no set migratory pattern, but rather
opportunistic responses to either rainfall or drought. In high rainfall
years, emigration occurs from the south west and south east into the
interior, with a reverse immigration to these heartlands in drier years.
When rain does fall in the arid central regions, Black Swans will migrate to
these areas to nest and raise their young. However, should dry conditions
return before the young have been raised, the adult birds will abandon the
nests and their eggs or cygnets and return to wetter areas.[8]
Black Swans, like many other water fowl, lose all their flight feathers at
once when they moult after breeding, and they are unable to fly for about a
month. During this time they will usually settle on large, open waters for
safety. [8]
Introduced populations
Prior to the arrival of the Māori in New Zealand, a sub-species of the Black
Swan known as the New Zealand Swan had developed in the islands, but was
apparently hunted to extinction. In 1864 the Australian Black Swan was
introduced to New Zealand as an ornamental waterfowl, and populations are
now common on larger coastal or inland lakes, especially Rotorua Lakes, Lake
Wairarapa and Lake Ellesmere, and the Chatham Islands.[4] Black Swans have
also naturally flown to New Zealand, leading some people to consider them a
native rather than exotic species, although the present population appears
to be largely descended from deliberate introductions.[9]
The Black Swan is also very popular as an ornamental waterbird in Western
Europe, especially Britain, and escapes are commonly reported. As yet the
population in Britain is not considered to be self-sustaining and so the
species is not afforded admission to the official British List, but the
Wildfowl and Wetlands Trust have recorded a maximum of nine breeding pairs
in the UK in 2001, with an estimate of 43 feral birds in 2003/04 (though
that is undoubtedly an under-estimate given the level of monitoring
undertaken).
Behaviour
Bearing
When swimming, Black Swans hold their necks arched or erect, and often carry
their feathers or wings raised in an aggressive display. In flight, a wedge
of Black Swans will form as a line or a V, with the individual birds flying
strongly with undulating long necks, making whistling sounds with their
wings and baying, bugling or trumpeting calls.[3]
Nesting
Generally, Black Swans nest in the wetter winter months (February to
September), occasionally in large colonies. A typical clutch contains 4 to 8
greenish-white eggs that are incubated for about 35-40 days.[10] After
hatching the cygnets are tended by the parents for about 6 months until
fledging, and may ride on their parent's back for longer trips into deeper
water. [3][4][11]
A Black Swan nest is essentially a large heap or mound of reeds, grasses and
weeds between 1 and 1.5 metres in diameter and up to 1 metre high, in
shallow water or on islands.[3][8] A nest is reused every year, restored or
rebuilt as needed. Both parents share the care of the nest. Like other
swans, the Black Swan is largely monogamous, pairing for life (about 6%
divorce rate).[12] Recent studies have shown that around a third of all
broods exhibit extra-pair paternity.[13]
Sexuality
A recent (2007) exhibition at the University of Oslo Natural History Museum
in Norway called Against Nature? explored homosexual behaviours in a number
of species, including Black Swans.
Several swan species exhibit lifelong homosocial behaviours, and the same
phenomenon can also be found in a number of other water-birds, notably geese
and flamingos, where it serves as a flexible life strategy.
In swans, the pair is the central social unit. The birds reinforce the unit
with frequent preening and sex. Should one die, the other will usually live
out the remainder of its life alone. The pair builds nests, raise cygnets
and defends a territory. Two cobs, being bigger and stronger than a cob and
a pen, can hold down a larger territory, and provide their cygnets with more
to eat.
Such same-sex pairs represent a major fitness bonus to a pen, and pens
without partners will seek out these couples, have sex with one or other of
the cobs and lay eggs in their nest. She is then chased off, not being a
part of the pair, and the cobs raise the cygnets themselves. Having access
to more food the brood have up to ten times the survival rate of a brood
with a heterosexual swan couple. From an evolutionary point of view, this is
a very rewarding strategy for the cobs as well.
This situation only holds true as long as a nest and a territory is in short
supply. The two males will have a fitness loss in that they (1) have no
guarantee they are the actual fathers of the cygnets (not being bonded with
the female) and (2) will anyway have to split reproduction between them.
A same-sex lifestyle will be advantageous in some situations, but not in
others. However, having a partner is a requisite for building a nest and
keeping a territory, and an opposite-sex partner may not always be available
when forming pairs. Thus, the ability to form a male pair is a normal part
of the Black Swans social behaviour and an example of a flexible life
strategy in the species.[14]
The Black Swan is evaluated as Least Concern on the IUCN Red List of
Threatened Species.