Saving the amazing Red Knot from extinction — it’s complicated
By Lynn Davis, College of Natural Resources and Environment
The remote barrier islands off Virginia's Eastern Shore provide a key staging area for migratory shorebirds, including the imperiled red knot. These islands are a critical stopover and feeding site. Rusty red-breasted during mating season, the red knot is about the size of a robin, belongs to the sandpiper family, and migrates from wintering areas at the southern tip of South America to breeding areas in Arctic Canada. Researchers estimate that 90 percent of the surviving Atlantic red knot population visits the Delaware Bay, Cape May, and Virginia's Eastern Shore to feed on billions of horseshoe crab eggs in the Delaware Bay and surf clams in Virginia. The stop to refuel is what enables the knot to complete migration.
"The red knots have declined substantially in the past two decades," says Jim Fraser, wildlife professor in Virginia Tech's College of Natural Resources and Environment. "Populations wintering in South America are now less than half what they were in 1980." The decrease is partly due to the decrease in the horseshoe crab populations, which in turn may be due to the heavy harvesting of the crabs for bait used to fish for conch and eel, he says.
Fraser's team began red knot research in 2005 in the Delaware Bay, where most of the horseshoe crabs lay their eggs. "We wanted to find out if that decreasing food supply was contributing to the knots' decline," says Sarah Karpanty, assistant professor. "When we heard that some of the knots were foraging along Virginia's Eastern Shore, we moved our research there and learned their food source is different on the Eastern Shore. The shoreline foraging bird loves donax, the hard-shell clam abundant on the barrier islands, the wildest section of the U.S. Atlantic Coast and a special place for birds."
With the sea level rising annually, however, these islands may someday disappear into the ocean. The northern end of Wreck Island, for instance, has lost 300 yards in recent years to the encroaching ocean.
The researchers do their fieldwork off the southern tip of the Delmarva Peninsula on islands between the Eastern Shore and the Atlantic Ocean, where there are sloping sandy beaches and wave action. Now known as the Virginia Coast Preserve and protected by the Nature Conservancy and other partners, including NASA, the 60-mile chain of 14 islands serves as one of the most important migratory bird habitats on Earth and comprises the longest expanse of pristine coastal wilderness and virgin beaches on the East Coast. The protected region also encompasses key mainland preserves that buffer the highly productive fish nurseries in the freshwater marsh lagoons and bogs.
North to south, the larger barrier islands are Chincoteague, Assateague, Wallops, Assawoman, Metompkin, Cedar, Paramore, Hog, Cobb, Wreck, Ship Shoal, Myrtle, Mockhorn, and Smith. Some of the islands were thinly populated for 300 years before major storms, such as the hurricane of 1933, eroded the land, put the villages under water, flattened sand dunes, and killed many of the pine trees. Hog Island, for example, once had 250 inhabitants and now has only a deserted Coast Guard station. Today, fishing, boat building, agriculture, and seafood businesses featuring oysters, clams, and scallops define the sparsely populated peninsula between the barrier islands and the Chesapeake Bay.
"In May, the red knots arrive, feathers and bone after traveling 4,000 miles from Tierra del Fuego, Chile, in only four days. The birds spend only a couple of weeks feeding and resting," says Karpanty.
The Delaware Bay-Eastern Shore staging area is critical for their survival because it is their only stop before continuing to the still-frozen Arctic breeding grounds, such as Cambridge Bay at 69 degrees north latitude, where food won't become available until later in the summer. "It takes the knot two to three days of non-stop flying, if the winds are favorable," says Jonathan Cohen, research project coordinator. "There are some indications that the birds know to wait for the tailwinds."
At the tundra they complete their breeding plumage, which blends in with the environment. "Their territorial song is unmatched by any other bird," says Cohen. "The chicks hatch at the exact time as the insects, so nature provides an available food source. The precise timing of all this is critical to their survival."
The Canadian Wildlife Service has found that lower-weight birds are less likely to be seen in the Arctic, which may have been a hindering factor in Cohen and Fraser's research.
"We do not know much about the reproduction of the knots, but we do know that if the birds do not have enough fat reserve, they can't reproduce," Fraser says. "When a red knot arrives on our coast, it can weigh as little as 90 grams; it needs to leave weighing at least 180 grams, preferably 220 grams, for survival, but unfortunately that is not happening."
In 1997, the knots gained about eight grams a day; now they are gaining only two grams. The Virginia Tech researchers have compared the caloric content of donax with the horseshoe crab eggs, and estimate a knot would have to eat 24,100 quarter-inch bivalves to match 24,000 eggs; but missing parts of the equation are the amount of energy it takes to digest each and the constraints, if any, posed by eating hard-shelled prey. "Basically, we don't know how the birds achieve the needed weight foraging on donax, but they seem to do it," says Fraser. "One possibility is that they keep foraging through the night."
Why care about the red knot? Fraser answers, "The knots' range used to be more coastal and wider, but the development and human population pressures along the Atlantic coast are taking stopover habitat away from the knots. In the 1850s, Cape May had a population of 25,000 red knots; today there are hardly any. In the old days, red knots and other shorebirds were harvested in large numbers. Today coastal development threatens the knots and many other species, and we believe that every living thing ought to have a chance to live. Humankind really can't successfully live without wild things. This is the lesson the red knot is teaching us."
Another piece to the puzzle of knot survival might be the lemming, a small rodent that lives in the Arctic tundra. They too are in decline and may be evidence of Arctic habitat degradation, which may in turn be affecting the red knot. "When the lemmings are in abundance, owls and foxes feed on them, but when their population is down, the owls and foxes switch over to eating the red knot and other birds," Fraser hypothesizes. "The peak in lemming numbers, which used to occur every three to four years, may be attenuated, possibly due to global warming reducing their habitat space."
With the tundra thawing, the pockets of space between the ground and snow, where the lemmings, live are disappearing. The red knots appear to do better when Arctic winters have been the worst – possibly because there were more lemmings sharing the area.
As summer ends, the knots, in common with many other migratory birds, do not rush to their winter home. They take their time, spread out, and stop at various places along the way back to Chile. Some knots winter in Texas and a few stop in Florida, but most of them return to South America.
North America's largest peep and one of the most colorful, the amazing red knot makes the longest yearly migration of any bird, traveling 9,300 miles from its Arctic breeding grounds in the sparsely vegetated hillsides of the tundra to Tierra del Fuego in southern South America after its June-to-August breeding season. The incredible bird reverses the trip in May.
"A 15-year-old knot will have flown enough miles in its annual migration to have taken it to the moon and back," says Cohen, "which is why banded red knots known to be 15 years or older are called 'moon birds' by researchers."
Trapping and tracking
How does the research team do its work? A boat ride out to the islands each day for a pleasant time on the beach? Think again. My experience as a volunteer was grueling. There are equipment failures; several-mile treks along open, hot beaches and through slippery mud with hidden holes in the tall, mosquito-infested grasses; buggy dunes where you need to hide until the cannon-nets are shot out; every kind of weather imaginable from cold, wet, windy days to blistering sun; and ever-changing tides to contend with in getting out to and back from the islands while trying to time the high tide on the beach for successful cannon-netting – the method used to capture birds for measurement without harming them. The researchers have only two to three weeks to collect data; so no matter what the weather, they are out with no cover, all day, every day.
Cohen, former postdoctoral researcher at Virginia Tech who is now an assistant professor of wildlife ecology at the State University of New York, is Fraser and Karpanty's operations planner. Depending on all the variables involved, from the day's weather forecast to the tide times, he sets up the daily sampling operation, determines which island gets sampled, and rotates daily duties with each of the summer technicians, who include graduate students Brian Gerber and Mary Kotswar, senior wildlife major George Cummins, Nature Conservancy biologist Barry Truitt, skipper captain Jim Clark, and research technicians Belita Gerber and Jason Hanser. Two of the team members are boat captains, and Jim Fraser and his son Donald also often motor the crews to the islands. One crew does cannon-netting on an island, while another takes donax samplings on a different island to avoid spooking the knots that the netting crew wants to capture and tag.
The pilot of a small plane takes Cohen on a daily flyover along the entire string of islands so he can scan his randomly placed sample areas using GPS locations, record bird counts within a 100-meter circle, and radio the knots' whereabouts to his ground crew so they can figure out where to station the 30-by-50 foot cannon-net.
Cohen has been able to radio-tag about 50 red knots a year. It takes each of the two teams an hour to boat out through the quagmire of marshes and some open water, depending on the tide, to the designated study island for that day. Once the researchers dock, usually on the mainland side of the island for safety, they carry a lot of gear over to the Atlantic Ocean side and backpack several miles down the beach to an area where Cohen believes the knots will come to eat. At that site, they strategically place a rolled-up net covered with sand near where the tides will wash up the donax. Referring to themselves as "techies," they place conch shells that look natural to the birds at each end of the netting so the researchers know where the covered net is in order to deploy it as the birds approach.
An assembly rig with an attached electric cord buried under the sand and leading to a battery hidden behind the dunes is what propels the net out over the birds when one of the team members hits the power switch. Once they put the cannon-net in place, the team members scamper behind the dunes so they are out of sight of the wary species. As the tide creeps in, the red knots follow the water's edge so they can peck at the donax. Some of the other researchers, called "twinklers" in this operation, have strategically positioned themselves at each end of the island so they can quietly walk and push a descending flock toward the cannon net. "We time our operation to set the net on a rising tide," Cohen says, "so the rising water pushes the birds toward the net."
Cohen, watching from farther down the beach with high-powered binoculars, gives the hiding cannon shooter the signal to deploy the net. Then all groups quickly move in to perform the next round of duties.
The researchers carefully put each red knot into a holding tube so they do not harm the bird, and the knots are measured for their bill length, weighed, and banded for radio-tracking. These measurements are helpful in showing the bird's health. For international tracking, red bands signify banding took place in Chile; green bands in the U.S.; and white bands in the Arctic.
Fraser says of cannon-netting, "Until you have seen it yourself, you can't appreciate how delicate the maneuver is. Even other feeding shorebirds, such as the sanderlings, add to the complications."
The bands, or tags, on the red knots can allow researchers using GPS units to track where the birds travel. When Cohen flies over the barrier islands, one of his tasks is to try to pick up sounds that reveal the locations of knots already banded. One goal of all this is to understand the knots' feeding movements.
While one crew does cannon-netting, the other group is walking a stretch of shoreline to collect sand samples containing the tiny donax clams to freeze and take back to their lab at the College of Natural Resources and Environment to do number counts later. Understanding how available and nutritional is the knots' food supply might give some insight as to why the knot population has been crashing. "In May and June of 2010, we found only a fourth of the migration population that normally stops over on the Eastern Shore," Fraser says. "Some scientists don't believe a diet of only clams is nutritional enough for the knots to survive migration, that they need the nutrients found in the horseshoe crab eggs, which are not found on the Eastern Shore. The whole picture is unsettled. In analyzing the poop of the knots, we do know that the donax are a major food source for the knots stopping over on the barrier islands. Donax, by the way, are seldom found along the Delaware Bay."
After spending some uncomfortable overnights on the peat banks of Wreck Island to verify calculations that the birds would need to feed around the clock to get their weight up for the Arctic journey, Cohen's field associate Brian Gerber discovered that the birds often do forage at night, blue mussels being one of their favorite foods.
During the last three weeks of May, when all the field work is done, one group of the research team headquarters at the Anheuser-Busch Coastal Research Center of the University of Virginia in the small town of Oyster. There, Fraser, Karpanty, and their graduate students have access to labs, boats, equipped offices, meeting rooms, workshop, and furnished dormitories with kitchen facilities. Another part of the research team lives in a rented house north of Oyster at Watchepreague so members can boat to some of the islands more quickly.
While bird trapping and radio-tracking have given scientists new insights into the knot's life cycle, many questions remain, including what signals the birds to leave Chile, to know where and when to land for the food stop-over, and to depart the Arctic. To find the answers, the field technicians have to be more creative than artists, more resourceful than engineers, and more passionate than Hokie fans. Just trying to figure out where and when to place the cannon-net to catch the wariest of birds in a constantly changing environment would challenge any chess player. In the meantime, how would anyone not want these magnificent little creatures to continue to exist?
Lynn Davis spent a week one May with Jim Fraser and his ace research team at the Coastal Research Station, where she participated in the cannon-netting and flyovers along the barrier islands of Virginia's Eastern Shore.