Now for some of the species that
were too large for the normal collection and they are large in every sense of
the word. Beware there will be a lot of superlatives!
Ostrich – Struthio camelus
Behold, the largest species of
bird in the world! Well that was obviously no surprise but even though
ostriches are well known they are still very impressive beasts. Males can stand
up to 2.8 m high and weigh in at 145 kg plus they also hold the land-speed record for
birds, running at speeds of 70 km/h. Ostriches also lay the largest eggs of any
birds, 20 times the weight of a chicken's, yet the eggs are the smallest in relation
to body size of any bird.
The two ostriches (S. camelus and the Somali ostrich S. molybdophanes) are ratites, a term
generally reserved for flightless birds of the order Struthioniformes including
emus, rheas, cassowaries and kiwis. With the flux of modern taxonomy, the
validity of this clade is in question as the volant tinamous should be nested
within the flightless birds suggesting independent routes to flightlessness. As
well as the extant ratites, there were larger and more bizarre members of the
group. On New Zealand the moas reigned supreme until the relatively recent immigration of Mouris whilst on Madagascar, the huge
elephant birds stalked the forest.
Together the ratites have a
Gondwanan distribution. This refers to a geographical distribution of organisms
contingent on the past arrangement of continents. During the evolution of birds
in the Cretaceous, ancestors of the ratites were distributed over the southern
continent of Gondwana (South America, Africa, India, Australasia and Antarctica).
Once Gondwana began to break up during this period, each new continent took its
own ratites. Emus, cassowaries, kiwis and moas evolved in Australasia, South
America evolved rheas and Africa took the ostriches. Well at least that was the
traditional view; more recent genetic work places the separation of these
lineages as more recent than the continental splits. This implies that volant
ancestors colonised the different continents and independently became
flightless, probably in lieu of the lack of large terrestrial vertebrates following
the extinction of the dinosaurs.
Southern Cassowary – Casuarius casuarius
Speaking of dinosaurs, the southern
cassowary could be lifted straight from the Cretaceous! Of the three
Australasian cassowaries, the southern cassowary is the largest and its bright
blue neck with pink wattles stands out against the black, ‘furry’ body. It is
the species of most relevance to me as I was lucky enough to see several
individuals of this vulnerable, enigmatic species in the wild whilst
undertaking fieldwork in the rainforests of Far North Queensland. One encounter
stands out in particular.
My friend, Emily, and I were
stepping along one of our paths into the rainforest when Emily froze and
back-tracked suddenly, cursing as she went! I then spotted the issue when
I noticed a cassowary standing about 15 m ahead. My first thought was ‘photo
opportunity’, so I whipped out my phone and took terrible snaps. But then it
turned to face us. We did nothing at first until it started walking towards us.
Suddenly, through my mind flashed the stories of people being head-butted with
their huge casques or lacerated with their elongated claws. We started walking
back down the track but the cassowary began to pick up the pace. The more we
sped up, the more it did, until soon we were running as fast as we could which
was difficult due to the suddenly claustrophobic foliage and lianas. Finally
(after what was probably just seconds) we emerged into the sun light and the
cassowary did not follow. Our hearts thumping, we regained our composure but
the fear of that encounter remained for the duration of our work!
Green peafowl – Pavo muticus
I have to admit I did not know
what this species looked like beforehand but being a congener of the familiar
peacock (Indian peafowl, Pavo cristatus)
I surmised correctly that it would be impressive. Moreover, the unfamiliarity
gives it an exotic feel where we might take peacocks for granted. This denizen
of Southeast Asian forests shares many of the traits that make the peacock
famous including the huge ‘tail’ of many eyes which is actually formed from
upper tail coverts rather than the rectrices. The tail of the peacock is famous
in biology as the pin-up for sexual selection. That such an elaborate ornament
should evolve under natural selection troubled Charles Darwin greatly who said
that ‘the sight of a feather in a peacock’s tail, whenever I gaze at it, makes
me sick!’ In time, Darwin, and the generations of biologists to follow, have
expounded theories of sexual selection which explain the ornaments of peacocks
and other animals. Whether choosing ornamented males for their sexy sons are
their good genes, it seems that beauty is the way to go.
Emperor penguin – Aptenodytes forsteri
Of the 19 penguin species, the
emperor is the largest, as the name might suggest. It is also the only bird
species to breed in the Antarctic winter. The emperor penguins are famous for
their annual 100 km trek into the Antarctic desert whereupon they breed, the
female laying a single egg. The first duty of the male is incubation so that
the female might return to the sea to breed. The egg is passed carefully between
the feet of the male to the female, avoiding the lethally cold ground at all
costs. With the female departed the male must while away the winter months, burning
precious fat reserves until the female returns. During this time, huddling is
imperative to conserve heat as are the suite of hypothermic adaptations
including blubber, down and the most densely packed feathers of any bird which
can be erected to trap additional air.
Soon after the chick hatches it
is fed its first protein rich regurgitation.Then, the female returns
with her own supply, locating the male through vocal recognition and relieving him of his duties so that he can travel back to the sea. Thereafter, rearing the chick is taken
in turn. The free parent must run a gauntlet of leopard seals and orcas to
reach open water whereupon they may fly through the water, diving up to 500 m
deep, feasting upon Antarctic fish, squid and krill.
A month and a half into
life and the chicks are big enough to be left alone whilst the parent both feed
at sea. This is not really ‘alone’, however, as the chicks form large crèches,
avoiding the bitter wind and the predatory Southern giant petrels. As summer
approaches, the chicks begin to moult into juvenile plumage and make to join
their parents in the booming summer seas which, by this point, are considerably
closer owing to the melting sea ice.
Wandering albatross – Diomedia exulans
The wandering albatross has the
largest wingspan of any living bird at up to 3.5 m (11 ft 6 in) which is
slightly absurd if you think about it. Most of their life is spent at sea with monogamous adults only returning
to land to dance and breed on rocky islands in the Southern Ocean. They are at the slowest end of the life-history continuum. The life-history continuum represents the
trade-off that all organisms have to face: whether to live longer or reproduce
more. Large organisms tend to be at the slow end and wandering albatrosses can
live beyond 50 and reach sexual maturity in their teens, thereafter only rearing
one chick every two years.
Whilst the generic name Diomedia references the Ancient Greek hero of the Trojan War.
Diomedes, who’s companions transformed into birds, the specific epithet exulans means ‘exile’ or ‘wanderer’
noting the vast areas this albatross covers. One impressive individual was
observed to travel 6,000 km in just 12 days.
The albatross is famous for its
role in the Rime of the Ancient Mariner,
the epic poem by Samuel Taylor Coleridge, where the ‘bird of good omen’ was a
welcome companion to the sailors and where the killing of one is a terrible
crime resulting in the burden of an albatross around the neck. Today, it is
humans that are the harbingers of doom for the albatrosses as plastic pollution
threatens colonies around the world.
