THE wind scours the island at a steady 40 kilometres an hour. Dozens of
mother gulls are riding it, each hovering protectively above her downy chicks.
One of the birds descends and delivers a swift kick to the back of Julie
Thayer’s head. Thayer winces, then goes about her business. Gales, guano and the
occasional kick in the head are all in a day’s work for a seabird biologist.
Año Nuevo Island, off the coast of central California, is one of a
string of 11 sites along the coastline of North America that Thayer and her
colleagues are studying to assess the impact of El Niño in the eastern
Pacific. By studying seabirds in an area encompassing over 30° of latitude,
from Prince Island in southern California to a cliff in Norton Sound, off the
central Alaskan coast, they are building a window on the health of the region’s
entire marine ecosystem.
“Birds are great biological sampling devices, because if they don’t find prey
then they don’t survive,” says William Sydeman, director of the Marine Studies
Program at Point Reyes Bird Observatory, and the principal investigator on the
study. “And birds are inexpensive to study, in comparison to the cost of running
an oceanographic research vessel.”
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This year’s El Niño, the strongest ever recorded, may be on the wane,
but in the eastern Pacific it continues to cause famine at sea. You might never
guess it from the cacophony of nesting gulls and cormorants on Año Nuevo,
but California’s seabirds are suffering. And as far north as British Columbia,
the researchers are finding a similar pattern of breeding failures. “Most of the
prey species that the birds feed on, like squid and rockfish and different
species of zooplankton, are nonexistent,” says Sydeman. “The birds can’t find
food, and people who are surveying small fish and zooplankton by sampling from
ships can’t find anything either. The food web just didn’t develop this
˛â±đ˛ą°ů.”
Sydeman has spent much of his career studying wildlife in the Farallon
Islands. On this small group of windswept rocks 35 kilometres offshore from San
Francisco, throngs of breeding birds, sea lions and elephant seals gather every
spring and summer. These creatures rely on the waters surrounding the islands,
some of the most productive in the world, to feed themselves and their
young.
The prevailing marine currents have created the area’s biological abundance.
The California Current, which flows south along the coast from Alaska, carries
nutrients from cold northern waters. As it moves, it is displaced to the west by
the force of the Earth’s rotation. This displacement pulls more cold,
nutrient-rich water up from the bottom to the surface and sets the stage for an
explosion of growth. Tiny marine plants—phytoplankton—thrive. Small
animals that drift with the currents—the zooplankton—feast on the
plants. In most years, all kinds of marine creatures reap rich harvests.
During El Niño events, however, a layer of warm surface water moves in
from the south and west, trapping the colder waters at deep levels. With vital
nutrients such as nitrogen and phosphorus locked away far deeper than the Sun’s
rays can penetrate, the phytoplankton that support the rest of the food web
cannot grow. In hungry times like these, few seabirds will be able to find
enough food for themselves, let alone their chicks.
This breeding season has seen a long list of casualties. Many species,
including brown pelicans, are abandoning their nesting colonies in southern
California long before any chicks have fledged. At Año Nuevo and the
Farallon Islands the birds are nesting late, and far fewer than usual are
attempting to nest. Where chicks are produced, the mortality rate is high.
Under the boardwalk
Gulls are the most obvious seabirds on Año Nuevo, noisily going about
their parental business over much of the island’s surface. But Sydeman and
Thayer are here to study rhinoceros auklets—podgy, eccentric-looking
seabirds that nest in underground burrows. The island is riddled with auklet
burrows, so as the researchers move about they carry wooden boards that they
place on the ground and use to walk on. The boards distribute their weight and
ensure that they won’t accidentally crush a burrow.
At each burrow’s entrance, Thayer stops and sets up her rhino auklet
surveillance equipment: a small infrared video camera mounted at the end of a
long cable. As the cable snakes down the burrow, a chick hoves into view. It is
alone in the burrow, which means that both its parents are out foraging at sea.
They’ll return in the evening, carrying fish to feed their baby. “He’s doing
fine,” says Thayer. “He’s a little downy fluffball.” This bird may be one of the
lucky ones. “Most rhino auklet chicks that reach that late a stage will fledge,”
says Sydeman. “If there’s going to be mortality, it tends to happen earlier in
the developmental pattern.”
Rhino auklets are one of three related species being scrutinised for the El
Niño study. Along with Cassin’s auklet and common murres, they belong to
the alcid family. All dive for food and “fly” under water, propelling themselves
with their wings rather than their feet. But they occupy different positions in
the food web. The Cassin’s auklet is a planktivore, feeding on small,
free-floating animals. The common murre eats fish and plankton and the rhino
auklet is a strict fish eater.
This summer, biologists have spent long hours patiently watching from hides
on islands up and down the Pacific coast to see what food adult birds bring back
for their chicks. The idea is that this indicates the state of the marine food
web more directly than human devices for sampling populations of sea creatures.
Birds may not be unbiased in the way a researcher sampling from a ship would be.
They may select certain sizes of fish, or prefer certain species of zooplankton.
But they are, of necessity, expert at finding their prey—a process that
can be very difficult for shipbound scientists who must search a vast area of
water to find scattered schools of small marine animals.
“The birds can track the upper 100 metres of the water column for us,”
explains Sydeman. “This is the most productive region of the ocean, because
phytoplankton need light for photosynthesis, and light depletes rapidly at
depth.” Cassin’s auklets typically dive to about 30 metres, rhino auklets dive
to about 50 metres, and common murres may dive as deep as 200 metres but usually
forage between 50 and 100 metres from the surface.
As study subjects, the birds have other obvious advantages. They are far more
visible and easier to track than their prey. Moreover, their ability to find
food is directly tied to the timing and success of their breeding efforts.
Decreased breeding effort and delays in egg laying indicates that the adults
were having a lean time in late winter and early spring. Reproductive
success—how many chicks a nesting pair fledges—reflects the
productivity of the marine food web over several months, from the time adults
mate to the time the chicks head out on their own.
Based on results available so far, it appears that the Cassin’s auklet, the
planktivore in the study, is having more difficulties than the murre and the
rhino auklet. In California, the Cassin’s auklets showed the longest delay in
breeding of the three species. On the Farallon Islands, only about half the
population tried to breed and they were eight weeks late in laying their eggs.
The murres, which eat both fish and plankton, were about four weeks late in
laying, and only about 75 per cent of them tried to nest. The rhino auklets, the
strict fish eaters, were about two weeks late, and most of the population are
trying to breed.
There are several reasons for this disparity. Fish eaters, explains Sydeman,
can generally switch to alternative prey, whereas planktivores are more
constrained. Murres and rhino auklets are also larger and able to dive deeper
than Cassin’s auklet, so they can reach food unavailable to their smaller
cousin. This usually isn’t a problem because zooplankton tend to come to the
surface each evening. But in El Niño years, krill and other zooplankton
seem to stay at depth, presumably, says Sydeman, because there is little plant
material to graze on in the warm waters nearer the surface.
Changing diet
By monitoring the food that adults bring back to chicks, the researchers can
detect changes in the availability and distribution of prey. For example, the
rhino auklets in central California are eating a lot of Pacific saury, a fish
not normally common in their diet. The saury are found further offshore than the
rhino auklet’s usual diet of anchovies, and may be less affected by El
±·ľ±Ă±´Ç. Murres have opted for sardines, one of the few fish in the area
that prefer warmer waters, instead of their usual diet of rockfish and
anchovies. On Triangle Island in British Columbia, Cassin’s auklets are carrying
fish rather than phytoplankton to their hungry chicks.
Sydeman says that El Niño has had dramatic effects on bird colonies up
and down the west coast since the spring and summer of 1998. But these are not
always clear or simple. At Triangle Island, for example, Cassin’s auklets laid
their eggs about 10 days later than usual, used only about half the usual number
of burrows, and where chicks were produced, many died—up to 50 per cent in
some areas. Rhino auklets, on the other hand, laid their eggs early, and
although fewer birds nested, chick growth rates are faster than in the past two
years. Common murres seem to be having a normal year but, like rhino auklets,
are eating more sand eels.
Tatoosh Island, outside the Strait of Juan de Fuca between Vancouver and
Washington state, may be an important exception to the El Niño pattern.
Julia Parrish, an assistant research professor at the University of Washington,
is studying common murres on Tatoosh Island. This year most of the birds lost
their first eggs to predators—the number of bald eagles in the area has
suddenly tripled, for unknown reasons—and all the females laid replacement
eggs. “That’s an indication that the climate signal, should we pick it up, would
be weak,” says Parrish. “If they have enough body stores to make another egg,
they can’t be hurting that badly.”
Cold hotspots
Next to Tatoosh Island is a submarine canyon. As ocean currents run south
along the Washington coast, they cross the canyon at right angles, pulling cold
water up from the bottom. This localised upwelling persisted, despite the El
±·ľ±Ă±´Ç. “In effect, what you get is a hotspot of productivity,” says
Parrish. “If you can find a place in the nearshore marine environment in which
the seabirds are relatively unaffected by what is a regional or possibly global
physical phenomenon, it’s reasonable to assume that everything else in that area
is also relatively unaffected. That’s an area you might want to put some effort
into preserving.”
El Niño may have little effect on sea life as far north as Alaska. So
far, the birds are nesting right on schedule, and it seems to be a normal
breeding year. “There is no overall, massive signal,” says Vernon Byrd, a
biologist with the US Fish and Wildlife Service who is supervising studies of
seabird colonies in southeast Alaska and the Pribilof Islands in the Bering
Sea.
Any El Niño effect in Alaska will be difficult to assess, however.
“This far north, ocean current systems are more complex, and over the years
there’s been a lot of argument about what’s really going on,” says Scott Hatch,
a research wildlife biologist with the US Geological Survey’s Alaska Biological
Research Center. Hundreds of emaciated common murres washed up dead on Alaska’s
beaches last winter, and some observers were quick to pin the blame on El
±·ľ±Ă±´Ç.
But Hatch points out that several such mass deaths have been documented
during the past decade. “When strong winds are sustained over two- or three-week
periods, it just becomes too much for the birds to cope with and they start to
die off,” he says. “Since this occurs in years when there is no El Niño,
it would be premature to say El Niño is the cause.”
Sydeman is philosophical about the disastrous year the birds are experiencing
in California. In the years he has spent living closely with breeding seabirds
on the Farallon Islands, he has seen good times as well as bad. “Because El
Niño causes violent storms and flooding, people have tended to focus on
this negative event that happens once every five to seven years,” he says. “But
from an ecosystem perspective, El Niño is part of a cycle that includes
some very positive things.”
In a review of 21 years of data on the Farallon Island seabirds, Sydeman and
his coauthors found there were seven years of breeding failure—most
corresponding with El Niño events. These lean times were counterbalanced
by seven years of extremely high seabird productivity. Some of the bonanza years
for seabirds came with La Niña—the reverse phenomenon, when an
abundance of nutrient-rich, cold waters move to the eastern Pacific.
Whether a La Niña will occur next year remains uncertain. “We may
still see an El Niño effect into 1999,” says Sydeman, “because we’re
talking about large changes in water temperature over very large geographical
areas.” This study, however, should help make such predictions possible in the
future. It is part of the El Niño Quick Response Program, funded by the
US National Oceanic and Atmospheric Administration (NOAA), which aims to make
future events more predictable by increasing scientific understanding about El
Niño’s effects in the eastern Pacific.
“It is very unusual for NOAA to fund research on birds,” says John Gaynor, an
NOAA spokesperson, “but Sydeman’s research is a critical addition to the total
ecological picture on the west coast.” The benefits of working as part of a
broader programme are not lost on Sydeman. “All of us—oceanographers,
atmospheric scientists, biologists—can learn something from each other,”
he says. “To be able to meet with people who are studying El Niño’s
effects on storms in California, and then to ponder the connections to what I’m
seeing among the birds on Año Nuevo Island . . . that’s priceless.”
