Thousands of puffins perished in Alaska in a massive mortality event

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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