The citizens of St. Paul Island off the coast of Alaska are
used to finding the occasional seabird washed up on the shore. But until
recently, dead tufted puffins were rare finds, especially during the winter
months.
Now, something has changed. By the time January drew to a
close in 2017, the number of puffin carcasses had spiked into the hundreds,
their emaciated bodies pointing to a breakdown in the Bering Sea's food chain.
Sadly, it's a sight the island's citizens might need to get
used to.
A study conducted by US researchers determined the high
numbers of remains found by volunteer beach combers were just the tip of the
iceberg, representing a massive mortality event of up to 8,800 birds.
Members of St. Paul's Aleut community have a history of
working with the University of Washington's Coastal Observation and Seabird
Survey Team (COASST) citizen science program.
Every month the volunteers survey the remains of birds and
bits of marine debris left on the island's beaches, providing researchers with
a trove of information on the ecological health of the Bering Sea.
The number of dead seabirds washing up from late autumn
through winter usually isn't all that high. Among those they do find, tufted
puffins might only make up 1 percent of the finds.
Between October 2016 and January 2017, the remains of just
under 360 adult and juvenile seabirds were collected, measured, and recorded by
St. Paul's COASST members.
What was particularly surprising was nearly eight out of
every 10 were tufted puffins (Fratercula cirrhata). The rest were crested
auklets (Aethia cristatella), and a handful of horned puffins (F. corniculata).
It wasn't hard to work out the likely cause behind such an
unusual surge in deaths. Necropsies on several of the bodies confirmed they were
emaciated, with severe loss of mass in their wing muscles.
Ruling out various toxins and illnesses, it was fair to say
the birds simply starved to death.
Throw in the seasonal appearance of new flight feathers
after a moult, and we get a grim picture of starvation at a time when their
bodies were desperate for nutrients.
A few hundred birds mightn't seem like a big deal. But it
was what the volunteers didn't see that draws concern.
By analysing the winds and currents in the area and running
experiments to determine the direction the floating remains would take,
researchers have come up with some broad estimates on how many deaths this
small sample might represent.
At the lower end, a little over 3,000 birds might have
perished that season due to a food shortage. At the upper boundary, we could be
looking at 8,500 individuals.
The amount of tufted puffin remains indicates that more than
half of the population living around the local islands may have died. And, if
the higher estimates are accurate, it's possible nearly all of the puffins died
in this single event.
Large scale mortality events like these aren't unknown. In
1997, hundreds of thousands of emaciated short-tailed shearwaters (Puffinus
tenuirostris) were estimated have perished in the south-eastern Bering Sea.
Many events like these have been traced back to changes in
the abundance of zooplankton, typically due to localised rises in ocean
temperatures.
It's likely that a loss of food off the Alaskan coast was
also to blame here. A few more winter storms than usual might have also
contributed a final straw for birds already exhausted of energy.
We shouldn't be at all surprised. Warming waters in the far
north have been thought to have had a domino effect not just on seabirds in
recent years, but declines in the number of newborn whale calves.
Global warming only makes it more likely we'll see more of
these kinds of events in the future. How often populations will manage to
bounce back is left to be seen.
This research was published in PLOS One.
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