In the fall of 2014, West Coast residents
witnessed a strange, unprecedented ecological event. Tens of thousands of small
seabird carcasses washed ashore on beaches from California to British Columbia,
in what would become one of the largest bird die-offs ever recorded.
A network of more than 800 citizen scientists
responded as the birds, called Cassin’s auklets, turned up dead in droves along
the coast. Beach walkers and local residents recorded the location and date of
carcasses as they found them, entering the information into a real-time
database that helped state, tribal and federal wildlife experts track the mass
mortality event as it unfolded.
The efforts of these place-based data
collectors — along with data on temperature, ocean circulation and the
abundance of prey — have provided the first definitive answer to what killed
the seabirds: starvation, brought on by shifts in ocean conditions linked to a
An international team of about 20 researchers
from federal, state and provincial agencies, universities and wildlife
organizations published their conclusions in the April 16 edition of
Geophysical Research Letters. The study can be found at https://agupubs.onlinelibrary.wiley.com/doi/abs/10.1002/2017GL076164
“This paper is super important for the
scientific community because it nails the causality of a major die-off, which
is rare,” said senior author Julia Parrish, professor in the University of
Washington’s School of Aquatic and Fishery Sciences and executive director of
the Coastal Observation and Seabird Survey Team (COASST), one of the citizen
science groups that counted the carcasses.
“When we see these mass mortality events,
that’s the ecosystem saying, in big neon letters, that something is wrong. This
paper can be used as definitive proof of the impacts of a warming world, and
it’s a not a pretty picture,” Parrish added.
The team’s paper pinpoints starvation as the
cause of death for between 250,000 and 500,000 Cassin’s auklets in late 2014 to
early 2015. The birds’ main source of prey, aquatic zooplankton known as krill
and copepods, was found to be smaller and less abundant than in previous years,
forcing the seabirds to eat less nutritious “junk food” instead of their usual
nutrient- and energy-rich prey.
Cassin’s auklets are palm-sized, stocky
seabirds known for their remarkable ability to fly underwater in search of
food. They are a gregarious species that nest in colonies and migrate south
along the coast in early fall, after breeding.
Warmer surface water temperatures off the
Pacific coast — a phenomenon known as “the blob” — first occurred in the fall
and winter of 2013, and persisted through 2014 and 2015. This event was the
likely culprit for shifting the zooplankton “dinner table” toward less nutritious
species, the researchers found. Energy-rich copepods thrive in colder water.
When the massive marine heat wave spread along the coast, it swept in loads of
smaller, less nutritious copepods typically found in warmer southern waters.
Through the summer of 2014, ocean circulation
kept the blob at bay in the Pacific Northwest, creating a coastal wedge of cold
water full of energy-rich food just off the coast of Oregon and Washington. But
that refuge collapsed in mid-September when seasonal shifts in ocean circulation
changed. As a result, Cassin’s auklets migrating south after breeding off the
coast of British Columbia essentially lost their nearshore foraging habitat.
This study is the first to document the direct
link between marine heatwaves and marine bird mortality events, the authors
“A lot of the evidence points to there being a
very tangible link in the warming of the Pacific to changes in ecosystem
structure that ultimately led to seabird starvation,” said lead author Timothy
Jones, a UW postdoctoral researcher in aquatic and fishery sciences.
The warm “blob” sat at the surface of the
Pacific Ocean for more than three years. After the auklet die-off, four more
mass mortality events involving seabirds took place, occurring farther north
each time. Murres, puffins, and most recently short-tailed shearwaters and
northern fulmars in the Arctic experienced a similar fate as the auklets — as
far north as the Chukchi Sea.
“The Cassin’s auklets story is really the
opener of a saga of multiple seabird die-offs that are unprecedented, as far as
we know,” Jones said.
The story of the auklet die-off is likely to
repeat for other species under climate change, Parrish said. Researchers will
continue to draw upon and learn from this example.
“This was a unique opportunity to have a
window into the future,” she said. “We are getting a sense of what the
largescale ecosystem — the entire North Pacific up into the Bering and Chukchi
seas — might look like in the future, and where we will have winners and losers
and how we might see change. In that sense, it was a tremendous natural
The efforts of hundreds of beach walkers —
many of whom survey their local beach for seabird deaths each month — combined
with databases and the knowledge of scientists across many fields cracked the
mystery of the Cassin’s auklets with a level of precision that is hard to
replicate, the authors said. Critical to their success was the ability to
collaborate and share resources.
“The big lesson here is you have to work together
in the sandbox. No one on this author list has any hope of doing all that work
by themselves,” Parrish said. “We had incredible luck in that citizen
scientists were collecting for years the very data we needed to find the
This study was funded by the National Science
Foundation and the Washington Department of Fish and Wildlife.