I
|
t wasn’t
until I took my Australian Wildlife Biology unit in 2nd year bachelors
that I began to profoundly appreciate the sheer hugeness and diversity that
makes up the world of birds. It is a mysterious world, a kaleidoscopic world, a
complicated world – birds have captured my heart and I never want to stop delving
deeper into their world! Let’s start with a simple look into the
characteristics of our avian friends…
What
makes a bird a bird?
There are
some defining features which will let us know if we’re looking at a member of
the class Aves.
· Wings! (even
the ones that don’t fly)
· Feathers
made of keratin
· Jaw
(beak) with no teeth
· Hard-shelled
eggs
· Light
skeleton made of pneumatic bones that are reduced and fused
· Sternum (breastbone)
with keel
· Fused
furcula (wishbone)
· High
metabolic rate
· Endothermic
· 4-chambered
heart
What’s so
unique about birds?
Birds are
basically living dinosaurs! They are neither mammalian nor reptilian but
avian… birds are birds! From the class Aves, modern birds originated 65 million years ago.
Wings
This
class of organisms are unique in that they have wings. These wings are
equipped with keratinised feathers. Even the seemingly wingless emu and cassowary…
although they’ll never be able to grace the skies, they do still have vestigial
wings – wings that are remnants from their ancestors. This can be confirmed
by the presence of a small claw at the tip of their rudimentary
wing-structures.
Beak
Their
jaws are toothless beaks made of bone at the centre and keratin on the
outside.
Lightweight
skeleton
Pneumatic
bone
Otherwise,
how would they stay up in the air? Birds have a skeleton made of pneumatic
bone, which simply means that it’s ‘airy’ – it’s more hollowed with
larger air pockets, serving to increase oxygen and create an incredibly
lightweight structure.
Unlike
our dense bones, birds’ bones also bear a honeycomb structure on the
inside, further adding to the airiness. Clever.
Reduction
and fusion
Bone reduction
and fusion also contributes to the lightness. Instead of having multiple
little bones, they’ve been reduced in numbers through the fusion of parts of
the skeleton. For example, the pygostyle is the fused caudal vertebrae,
the furcula is the fused left and right clavicles (collarbone), and the tibiotarsus
is the fused tibia (shinbone) and tarsus (ankle).
Centralisation
There’s
more! Centralisation plays a key role in making the skeleton suitable for
flying. The centre of gravity is appropriately centralised to the middle of the
body under the wings – you wouldn’t want a heavy tail or a boulder of a head!
That’s why long necks are capable of S-shaped retractions and they have smaller,
lighter distal bones (at the extremities e.g. fingers, lower vertebrae).
Keel and
sternum
And we mustn’t
forget about the keel-shaped sternum. On the bird’s chest is a broad, flat
keel extending from the sternum (the breastbone). If you’ve handled a hen or rooster, you’ve
probably noticed the curved protruding part down the middle of the chest; that’s
the keel. It is where the flight muscles attach, hence why birds that
are stronger flyers tend to have keels with larger surface areas whereas birds like
the emu have much smaller keels.
That’s
all for today! See you in my next article Xx
Sources:
Cole, L 2019,
BIOL2032 Australian Wildlife Biology, lecture: Birds: Internal Anatomy and
Physiology, lecture PowerPoint slides, Taronga Institute of Science and
Learning, The University of Sydney
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