16 Australian Geographic
NEED
TO KNOWwith Dr K arl K r uszelnick i
Fat birds
FOR MOST OF US, getting fatter has bad
health effects.
But it’s good for the bar-tailed
godwit, which can double its weight
in a week or so, and then burn it off
again in the same amount of time.
The bar-tailed godwit is a large wading
bird that breeds on the Arctic coasts
and tundra of Scandinavia, northern
Asia and Alaska.
Flocks fly south to cross the
equator and spend the northern
winter in warmer climates, such as in
New Zealand. In their search for the
eternal summer, forever avoiding
winter, they fly north again, leaving
New Zealand in March.
There are about 1.1 million
of the species worldwide, each
37–41cm long (bill to tail), with a
wingspan of 70–80cm. The males
(190–400g) are smaller than the
females (260–630g).
When birds migrate long distances,
they need lots of energy. They get
what they need to keep on flying
by burning up fat. Your averagenon-migrating bird carries only
3–5 per cent of its body weight as
fat. By comparison, if you fly further,
you need more padding.
Birds that migrate short distances
carry 20–30 per cent fat. But some
long-haul birds really ramp up their
body fat to 40–50 per cent.
Our heavy hitter, the bar-tailed
godwit, holds the record at a
whopping 55 per cent body fat!
This gives them enough energy to
make them the long-distance flight
champions – 11,680km non-stop
across the Pacific, in 8.1 days of
continuous flight.To prepare for the flight, bar-
tailed godwits do more than just pig
out and lay down fat. They can also
shrink a few organs not needed for
the migration (such as the liver,
kidneys and stomach), even while
they are flying.
By shrinking away non-essential
organs, they can drop their basal
metabolic rate by 42 per cent. Any
reduction in wasted energy is good
when making such an extreme flight.
Another advantage to shrinking
these organs is that they provide a
source of protein that is useful during
the flight.
As long as they can get their
obese bodies airborne, not only
do godwits get across the Pacific
in one single hop, they even arrive
for their holiday slimmed down to
their perfect beach body.DR KARL is a prolifi c broadcaster, author and
Julius Sumner Miller fellow in the School of
Physics at the University of Sydney. His latest
book, Vital Science, is published by Pan Macmillan.
Follow him on Twitter: @DoctorKarlPHOTO CREDITS,FROM TOP: SHUTTERSTOCK; SIMONE DE PEAK, NEWCASTLE HERALDSCIENTIFIC NAME:Limosa lapponicaFor nature’s sake
Wildlife artist James Hough donates his time and talent to
Tim Faulkner’s Aussie Ark through the AGS Art Calendar.I
T’S BEEN 30 years since we
first published our famous
Art Calendar. During that
time, many of Australia’s
finest wildlife artists have
contributed to this large-
format wall calendar, which,
in turn, has contributed funds
to wildlife conservation in
Australia with $2 from the
sale of each donated back to
the Australian Geographic
Society. We are thrilled to
announce that in 2020 we’ll
be introducing the skills and
talents of artist James Hough
to our dedicated Art Calendar
fans. A member of the
international Artists for
Conservation group,
Maitland-based James,
who originally trained as a
surveyor, has turned hispassion for the bush and its
creatures into a full-time
pursuit. He’s donated
13 paintings to the calendar,
and AUSTRALIAN GEOGRAPHIC
will donate $2 from each
calendar sold to Aussie Ark’s
captive breeding program.
australiangeographic.com.
au/shop/Bar-tailed godwit.A rt Calendar 2020
ARTWORK BY JAMES HOUGHEACH PURCHASE OF THIS GEOGRAPHIC SOCIETY IS DONATING $2 FROM THE AUSTRALIAN
CALENDAR TO AUSSIE ARKThe bush, and its inspiration, is never too far away from
James’s Maitland studio in the Hunter Valley region of NSW.