You are here

Terns of Endearment

Terns of Endearment header image
Research on the lives of fish-eating seabirds may deepen our understanding of the natural system that includes endangered salmon and steelhead.

It’s a big deal when wild, ocean-going salmon spawn, the climax of a life journey that puts fish through experiences in freshwater and saltwater that are more terrifying than any of the survival tests on "reality" television shows.

The fish spawn in shallow depressions biologists call redds. The female digs a redd in a gravelly stretch of stream bottom by rolling onto her side and moving her body like a hula dancer on amphetamines. In a day or two a single female is apt to build three or four redds and release hundreds or thousands of eggs, depending on her size and species. The male fertilizes the batches of eggs with clouds of sperm.

Caspian tern in flight with a fish in its beak.

A Caspian tern returns to its nest from a foraging trip. Photo: Lynn Ketchum

An area on Rice Island in the lower Columbia River, about 21 miles from the ocean, once used by a large breeding colony of Caspian terns. One winter, while the birds were away, a Caspian Tern Working Group altered the area, encouraging the birds to nest and breed downstream. Photo: Lynn Ketchum

To sustain a stream’s run, mathematically speaking, just two eggs from each pair of spawning salmon have to grow into a young female and a young male that will find their way to the same ocean their parents did, stay alive until instinct says it is time, then make it back to the spawning grounds to reproduce. So could the dining habits of seabirds that have taken up residence in the state’s biggest river contribute to the disruption of some wild salmon runs, as well as runs of hatchery salmon?

Scientists, graduate students, technicians and seasonal workers from Oregon State University’s Department of Fisheries and Wildlife are addressing parts of this complicated question. Their study of seabirds will help wildlife managers working with fish and fowl and provide valuable information for public decision-making on issues with environmental, economic and social implications.

"Holy cow. What is that," says Cari Cardoni, shifting forward in her chair in a crude hut, a blind for viewing wildlife that isn’t much bigger than the plastic outhouses you see at construction sites. Her eyes never leave huge binoculars as she looks out a small opening in the plywood wall. "The tern has blood all over him. That fish in his mouth is gigantic. It looks like a snake. No, it’s a lamprey. The tern can’t find his chicks. He dropped the lamprey. Uh oh, a gull got it."

This scene is playing out on a strip of land about a mile long and a quarter of a mile wide. It’s surrounded by the Columbia River, or more precisely, the estuary where the river’s freshwater mingles with saltwater from the Pacific Ocean as the tide comes in and goes out.

The strip of land is East Sand Island. If you stepped out of the little hut and looked north you’d see the Columbia’s shore a few hundred yards away and, beyond that, the green hills of Washington. East, upstream, you’d see the river retreating into the horizon toward Portland. South, and a little east, across a bridge four miles long, you’d see Oregon’s oldest city, Astoria, with soft light from a pale blue June sky illuminating the 125-foot Astoria Column that commemorates local history. The ocean is about five miles west, but the island is pretty much at sea level, so it would be just out of sight.

Cari Cardoni peering through binoculars. Thousands of terns on a sandy stretch of East Sand Island.

OSU employee Cari Cardoni collects data on Caspian terns on Eastern Sand Island in the Columbia River, about 5 miles from the ocean. Many of the birds moved there from Rice Island. Photo: Lynn Ketchum

The world's largest known breeding colony of Caspian terns, about 20,000 adults. This is in June during the peak of the breeding season. Members of a tern working group lured the colony to East Sand Island, from Rice Island, with techniques such as tern recordings and decoys. Photo: Lynn Ketchum

Then again, crawling out of the hut might be smarter. If you stepped out standing up straight, white missiles with black tops would lock onto you, diving, threatening to drive their scarlet bills into your skull, definitely trying to pierce your eardrums with hideous screeches.

Cari Cardoni knows. She came west from North Carolina a couple of years ago to do biology field work after graduating from college. This is her second summer as a seasonal employee on a study directed by Dan Roby, a federal wildlife ecologist stationed in OSU’s Department of Fisheries and Wildlife (see the sidebar below on federal-university collaboration in fish and wildlife research).

Cardoni’s focus is the world’s largest known breeding colony of Caspian terns, about 20,000 adults and their chicks nesting at the east end of the island. She has often seen the colony transformed from a feathery, undulating blanket spread across five acres of sand into a blizzard of wings. It happens when predators, or the occasional careless human, appear.

"Anytime adults flush (fly into the air)," Cardoni says, "their eggs and chicks are subject to predation by gulls. When bald eagles come near, the whole colony flushes. It’s an awesome sight. But not good for the colony."

Cardoni is a "colony monitor," one of two. The job sounds relaxing, but the hours staring through binoculars or a powerful spotting scope, meticulously recording what you see, can be intense.

She and the other monitor, Ian Rose, live on East Sand Island for six-day stretches, cooking on a camping stove and sleeping in small tents. They often relieve one another from shifts in a blind, crouching low as they come and go so they won’t disturb the birds. Other times they work simultaneously in blinds situated around the tern colony or join forces with graduate students and others for tasks that require several people. She and Rose never take the same day off. This is Rose’s 24-hour break period. He’s on the mainland showering, doing laundry, checking his e-mail and calling his parents back in Pennsylvania.

Scott Anderson and Jill Keep putting a band on a tern's leg. Eli Bridge with outstretched hands as a tern flys away.

OSU graduate student Scott Anderson, left, and technician Jill Keen put a color-coded leg band on an adult tern. This will help them track the bird's movements and survival. Photo: Lynn Ketchum

Graduate student Eli Bridge releases a tern. Terns banded in Oregon have been spotted as far south as the west coast of Mexico. Photo: Lynn Ketchum

Despite the proximity of civilization—the nearby town of Chinook on the Washington shore, and Astoria—East Sand Island is, as naturalist Charles Darwin might have put it, a little world unto itself.

Mice and other small mammals scurry through the willows, elderberry bushes, weeds and grasses. There are songbirds and nutria, aquatic rodents some people call water rats and others describe as small beavers. The island is really popular with marine birds, and not just terns.

Opportunistic gulls that prefer to nest in vegetative cover rather than the tern’s favored open-sand habitat lurk perpetually in tall grass near the tern colony waiting to steal eggs, or fish the terns bring to their nests, or tern chicks, dead or alive. In fact, one of the largest nesting colonies of western and glaucous-winged gulls on the West Coast pretty much surrounds the tern colony, and interbreeding between the two gull species adds hybrid gulls to the mix. A close relative of those creatures—the smaller ring-billed gull—also nests on East Sand Island.

There are other seabirds. In the past decade and a half an increasing number of California brown pelicans, an endangered species whose closest nesting colony is in southern California, have spent the night on the other end of the island from the tern colony, the west end. It’s the biggest brown pelican night roost in the Northwest, reaching up to 10,000 birds at times. In the rocks next to them is the Pacific Coast’s largest nesting colony of another seabird you see along much of the Oregon Coast, about 17,000 double-crested cormorants.

Throughout the day the seabirds of East Sand Island leave individually, or in small groups, to forage for up to several hours in the estuary or ocean.

Caspian terns are smaller than the island’s other seabirds, except for the ring-billed gulls, though they are the world’s largest tern. When they go fishing, the sleek, no-nonsense creatures rocket off the island near the water, bucking the usual headwinds coming in from the ocean. Cormorants and gulls leave at higher altitude. The black, long-necked cormorants resemble the Concorde supersonic airliner, while the gulls are like dark-hearted ballet dancers, glancing from side to side for an easy meal as they swirl away. Brown pelicans, the island’s biggest seabird, flap off with a distinctively slow rhythm.

Interest in seabirds near the mouth of the Columbia River intensified in recent decades as humans started wondering if their rising numbers had a negative impact on juvenile salmon on their way to the ocean.

California brown pelican with outstretched wings. A pair of gulls perched on a tree stump.

One of East Sand Island's California brown pelicans. This juvenile has a six-foot wingspan. The island's night roost is the largest in the Northwest, reaching up to 10,000 pelicans. Photo: Lynn Ketchum

This breeding pair of glaucous-winged/western gulls have nested near the breeding colony of Caspian terns on East Sand Island. The gulls steal much of their food—eggs, chicks and fish—from the terns. Photo: Lynn Ketchum

"The Columbia Basin is like a gigantic funnel," explains Dan Roby. "Each year hatcheries in Oregon, Washington and Idaho pump out about 150 to 200 million young salmon and steelhead of various kinds, and they—plus the wild salmon—all pass through the narrow bottleneck at the mouth of the Columbia."

Caspian terns, in particular, gained notoriety as salmon predators in the late 1990s.

Historically, some of the birds bred and raised their young during the spring and summer in Oregon at inland spots such as Malheur Lake in Harney County, and the Klamath Basin. They were first recorded nesting on the coast in the Northwest in 1957. By 1986 there was a nesting colony on Rice Island in the Columbia River estuary, about 21 miles from the ocean, as well as at sites much farther up the river.

Unlike East Sand Island, which nature built, Rice Island was constructed by humans from wastes dredged out of shipping lanes. Terns may have settled there because there was plenty of open, sandy habitat where they could nest and a ready food supply, Roby theorizes. Studies in 1997 and 1998 revealed that thousands of Caspian terns nesting on Rice Island were eating millions of young coho salmon, spring chinook salmon, fall chinook salmon and steelhead on their way to the ocean. Tags recovered at the tern colony, ones that had been implanted in young salmon and steelhead, proved that besides hatchery fish, the birds were consuming salmon and steelhead listed under the federal Endangered Species Act.

In July and August of 1998, with their chicks mature enough to fly, the terns of Rice Island headed south to their wintering grounds, which range from southern California all the way to the northern tip of South America. A surprise was waiting when they returned to Rice Island the following April to mate, build nests and raise a new generation.

Humans had made Rice Island less inviting and East Sand Island, where there was a greater variety of marine fishes for the terns to eat, more appealing. The plan was developed and executed by the Caspian Tern Working Group, an interagency group of resource managers that included representatives of the National Marine Fisheries Service, the U.S. Fish and Wildlife Service, the U.S. Army Corps of Engineers, the Oregon and Washington Departments of Fish and Wildlife, the Idaho Department of Fish and Game and the Columbia River Inter-Tribal Fish Commission, as well as OSU. The job of Dan Roby, his OSU students and technicians, and collaborators with the Columbia River Inter-Tribal Fish Commission was to help figure out how to convince the terns to switch nesting sites, and to evaluate the impact of the relocation effort.

Caspian tern feeding a fish to it's chick. Juvenile double-crested cormorant with its head in the mouth of its mother.

An East Sand Island Caspian tern gives its chick a surf perch. Photo: Lynn Ketchum

There are about 17,000 double-crested cormorants in the nesting colony on East Sand Island, the largest on the Pacific Coast. This juvenile is retrieving fish from its mother's stomach. Photo: Lynn Ketchum

On Rice Island, workers disrupted sandy areas where the terns had nested with tactics such as planting wheat and installing fencing. On East Sand Island, they removed vegetation and debris to create more desirable bare-sand nesting habitat for terns. They put out tern decoys and installed CD players and speakers so they could play recordings of tern sounds. They also harassed larger gulls that intruded on the new tern nesting area, including shooting some because, as Roby puts it, "gulls are extremely smart and persistent. If you aren’t serious, they figure it out very quickly."

Over the next two years, all of the terns moved from Rice Island to East Sand Island. The impact on young salmon was dramatic.

"In 1999 and 2000 the diet of terns nesting on Rice Island consisted of 77 percent and 90 percent juvenile salmonids, respectively," Roby and several co-authors wrote in a scientific journal article published recently, "while in 1999, 2000 and 2001 the diet of terns nesting on East Sand Island consisted of 46 percent, 47 percent, and 33 percent juvenile salmonids, respectively."

The terns are not only eating fewer young salmon and steelhead since humans encouraged the birds to switch nesting sites, OSU research shows. They are raising more young of their own successfully. Based on his research group’s findings, Roby speculates that one reason is the greater variety of food available nearer the mouth of the Columbia River.

Cardoni and Rose, the tern colony monitors, record what kind of food the terns bring back to the nesting colony.

"It’s called the meal delivery rate (MDR)," says Cardoni. "We watch one nest for a three-hour period and record how many chicks are fed and what kind of fish they eat." They also record what kinds of fish male terns bring to potential mates during courtship. In addition, during the nesting season researchers shoot a small number of terns and analyze what’s in their stomachs.

OSU seabird researchers. Tern colony with OSU research boat in background.

Some of the OSU seabird researchers on East Sand Island. Left to right: Ian Rose, a tern colony monitor; Anne Mary Myers, field crew leader; graduate student Sadie Wright; recent OSU graduate Garrett Dorsey; and project leader Dan Roby, a wildlife ecologist. Photo: Lynn Ketchum

OSU fisheries technicians, in the specially equipped boat, track juvenile salmonfitted with radio transmitters. That's the East Sand Island Caspian tern colony in the foreground. Photo: Lynn Ketchum

The research shows that the terns nesting on East Sand Island are consuming more marine forage fishes from the estuary and the ocean—such as herring, sardines, anchovies, smelt, surf perch and the Pacific sand lance—than terns nesting on Rice Island did. These fish tend to have a higher fat content than juvenile salmon headed for the ocean, providing additional calories and nutrients the terns need.

The tern colony monitors collaborate with five OSU graduate students working with Roby who are studying fish-eating birds in the Columbia River (see the sidebar on page 22 for information on the graduate students’ projects). Overall, the research is contributing to a clearer picture of how the seabirds impact the ecosystem, and how the ecosystem—including humans—impacts the birds. This may benefit salmon and seabirds.

"Some people have begun to hate terns," says Roby. "A few years ago a few fishermen dropped six raccoons and a couple of possums off on Rice Island (to prey on the birds). We had to run around trapping and removing the predators before they drove the colony away. But Caspian terns are a native species in our region and protected by the Migratory Bird Treaty Act. They also are beautiful birds with their own intrinsic value apart from their protected status.

"Our research indicates they aren’t specialized to eat young salmon and will readily use other types of forage fish. They’re just nesting where suitable habitat exists, and mostly eating what’s readily available nearby."

Carl Schreck is a federal fisheries biologist stationed in OSU’s Department of Fisheries and Wildlife (for more see the "historic partnership" sidebar, this page). His graduate students and technicians have tracked the movements of juvenile salmon and steelhead down the Columbia River to the ocean for more than a decade, trying to determine the fishes’ fates and learn how humans can help them in their migrations to the ocean and back upstream to spawn. Schreck’s group regularly works and shares information with Roby and his researchers. Schreck cautions that science is a fair distance from answering all the questions on how seabirds affect juvenile salmon, but he has an opinion:

"Salmon and seabirds evolved together over time. I think the birds in the Columbia River estuary are probably cropping out young salmon that are less fit. If they didn’t, other predators would probably get them in the ocean. My guess is that the seabirds would only impact a run of salmon negatively, only tip the natural balance, if the salmon run, the population, was not robust—was in trouble because of other factors."

Shaun Clemens punches buttons on fish tracking device. Juvenile sockeye salmon.

Ph.D student Shaun Clemens, supervised by OSU fisheries professor Carl Schreck, downloads fish tracking data from equipment on East Sand Island. This information will be correlated with data obtained by researchers in boats to develop a more comprehansive picture of the lives—anddeaths—of juvenile salmon migrating down the Columbia River to the ocean. Photo: Lynn Ketchum

Sockeye salmon—these are in an Idaho hatchery—used to travel up and down the Columbia River and many of its tributaries, but few are left. A deeper understanding of complex natural systems will help humans protect other types of salmon and steelhead, say OSU researchers. Photo: Natalie Forbes/Getty Images

Graduate Students Tackling Seabird Questions

Here’s a peek at the thesis projects of five graduate students from the Department of Fisheries and Wildlife in OSU’s College of Agricultural Sciences. Each is conducting research with seabirds under the supervision of OSU wildlife ecologist Dan Roby:

  • Scott Anderson, a master’s student from Avon, Connecticut, is studying breeding Caspian terns in the Columbia River estuary. This includes putting radio tags on terns, and gathering information such as what factors influence where the nesting terns forage and the type of fish they feed on.
  • Cindy Anderson (no relation to Scott Anderson), a master’s student from Forest, Ontario, Canada, is studying a nesting colony of about 17,000 double-crested cormorants on East Sand Island in the Columbia River estuary. For two field seasons, she monitored the colony’s size, nest site selection, reproductive success, and factors limiting colony size and nesting success. She also tracked radio-tagged birds to assess factors that limit where and how the cormorants forage, and characteristics that influence the colony’s impact on juvenile salmon in the estuary.
  • Michelle Antolos, a master’s student from Long Island, New York, is studying the breeding and foraging ecology of nesting colonies of Caspian terns in the mid-Columbia River region, above The Dalles. She has collected data on the colonies’ size, productivity and diet. The information will be important, she notes, "to policy-makers considering management of Caspian terns on that stretch of the Columbia River."
  • Sadie Wright, a master’s student from Juneau, Alaska, is studying the California brown pelicans that roost at night on East Sand Island. The birds are listed under the federal Endangered Species Act. She is quantifying factors that disturb the birds, potentially causing them to abandon the roost. "This information is essential for designing and implementing management plans for protecting California brown pelicans in the Columbia River estuary," says Wright.
  • Don Lyons, a Ph.D. student from Cedar Rapids, Iowa, is using a "bioenergetics modeling approach" to study the impact of Caspian terns and double-crested cormorants on the survival of endangered and threatened juvenile salmon and steelhead in the Columbia River estuary.
  • This includes collecting data on the type of fish the birds eat, the caloric content of each type of fish, how much energy each bird needs to perform its daily activities, and the size of the bird population. Based on such data, he estimates how many young salmon and steelhead the birds consume. Federal, state and tribal resource managers will use the information in evaluating whether the birds are limiting recovery of salmon and steelhead listed under the Endangered Species Act, Lyons says.

Oregon Benefits from this Historic Partnership

Since they were created in the 1930s, cooperative fish and wildlife units have conducted research that addresses complex natural resource issues across the country.

Today the university-based program is a partnership between the U.S. Geological Survey, host universities, state natural resource agencies, the U.S. Fish and Wildlife Service and the Wildlife Management Institute, a private, non-profit scientific and educational organization based in Washington, D.C.

The 39 cooperative research units across the country include the Oregon Cooperative Fish and Wildlife Research Unit at Oregon State University. Fisheries biologists Carl Schreck and Hiram Li are leader and assistant leader, respectively, of the unit’s fish program. Wildlife ecologists Bob Anthony and Dan Roby are leader and assistant leader of the unit’s wildlife program.

All four scientists have offices and labs in Nash Hall on the OSU campus, where the university’s Department of Fisheries and Wildlife is located, and are courtesy faculty members in the department.

"Our charge is to do research, work with graduate students and provide technical assistance and information to natural resource managers and the public," says Roby. "But the unit offers other benefits to Oregon, too. One is that by having the unit here, it is easier for federal money to come to OSU to address needs in the state."

Published in: Ecosystems, Water