ED YONG - Climate Change Is Shrinking Earth’s Far-Flying Birds
Every year, flocks of red knots criss-cross
the globe. In the summer, these shorebirds breed in the Arctic circle, making
the most of the exposed vegetation and constant daylight. Then, anticipating
the returning ice and continuous night, they fly to the opposite end of the
world. Different populations have their own itineraries, but all are epically
long: Alaska to Venezuela; Canada to Patagonia; Siberia to Australia.
These migratory
marathons mean that the red knot’s fate in one continent can be decided by
conditions half a world away. And that makes it a global indicator, a sentinel
for a changing world. It is the proverbial canary in the coalmine, except the
mine is the planet.
And the canary is
shrinking.
For the last 33 years,
European scientists have been measuring a population of red knots that stop at
Poland’s Gdansk Bay on their migrations between northern Russia and western
Africa. When Jan van Gils from the Royal Netherlands Institute for Sea Research
analyzed these measurements, he noticed that the knots have been gradually
getting smaller.
They’re
not alone. Israeli sparrows, Danish hawks, Alaskan polar bears, North Sea
fish, and many other animal populations are getting smaller as the world warms.
Some scientists suggest that the trend is adaptive: compact bodies are useful
in hotter conditions because smaller individuals have a larger surface area for
their size, and so lose heat more quickly. Others say it’s maladaptive: the
shrunken species are simply undernourished.
To find out which
explanation applied to the knots, van Gils analyzed satellite images of the
birds’ Russian breeding grounds. These pictures revealed that the region’s snow
has been melting earlier and earlier. Thirty years ago, it was disappearing in
mid-July. Now, it’s gone by late June, some two weeks prior. And the earlier
the melts happen, the smaller the young knots get.
Why? It’s probably
because red knot chicks mainly feed on the insects that emerge from defrosting
Arctic soil. If the snow melts too early, the hatchlings miss out on Peak
Insect and can’t eat enough to pack on weight. They end up small and stunted... read more:
