The Murre the Merrier
Decoys, mirrors and mood music lure gregarious seabirds back to abandoned breeding colonies
COMMON MURRES are extroverted birds. They summer in the midst of crowded, cacophonous parties--breeding colonies that draw hundreds to hundreds of thousands of these formally attired, black and white seabirds. So imagine one colony's reaction when, like humans emerging from a fallout shelter after war, the birds returned to their breeding rock one spring to find it completely deserted.
That's what happened 16 years ago to survivors of an oil spill, which had dumped 25,000 gallons of crude just outside San Francisco Bay a few months before the murres gathered together to breed. The spill killed more than 10,000 seabirds, including 6,300 common murres--about half of which had formerly nested on Devil's Slide Rock, a tiny island 15 miles south of San Francisco. For the next decade, not a single murre nested on the haunted rock.
Then in 1996, a few roving murres noticed a change in the old neighborhood. Suddenly, more than 300 of their brethren had settled atop the steep, jagged island. The newcomers were a bit stiff, but they seemed comfortable enough--and their very presence enticed some oil spill survivors to give Devil's Slide Rock a second chance.
Photo: © FRED BRUEMMER (PETER ARNOLD INC.)
PARTY ANIMALS: The common murre is a social seabird. After spending winter apart at sea, males and females rendezvous each spring to breed and raise chicks in densely packed colonies.
Those first new colonists, in fact, were wooden decoys, placed there by a troop of rock-climbing biologists hoping to lure murres back to the island to breed. The scientists also set up solar-powered speakers that broadcast the species' kazoolike calls, as well as mirrors to reflect the movements of any live murres that happened to show up. The ruse worked. That year, a few dozen murres flitted around the island, and six pairs actually bred there. "We were surprised there were any at all," confesses Steve Kress, the National Audubon Society ornithologist who pioneered the project's unusual methodology.
The work at Devil's Slide Rock is one of more than a dozen similar "social attraction" projects that Kress and other biologists have undertaken worldwide. Their experiments are designed to lure colonial seabirds to safer places to nest or, as in the case of the murres, to bring them back to breeding areas they have abandoned. So far, ornithologists have used decoys--with or without the extras of recorded song and mirrors--to attract terns, puffins, skimmers, gannets, petrels and other birds to breeding grounds from California and Maine to Hawaii, New Zealand and Japan.
Why work so hard tricking seabirds to nest on islands that they've shunned? Put simply, biologists do not like to put all their eggs in one basket. Birds that breed only in a few, concentrated colonies--as do many seabirds--are vulnerable to contagious diseases, killer storms, oil spills and other natural or man-made disasters. The more breeding colonies there are within a species' range, the better the chance that at least one population will survive the next crisis and live to build its numbers back up. Such insurance is increasingly important today as both seabird numbers and suitable habitat decline worldwide.
Consider the common murre. This species' populations have plummeted in most parts of its range, a vast area that arcs over the top of the Pacific Ocean from central California to Alaska and back down the Asian side to Japan. A symmetric arc of breeding territories in the Atlantic Ocean begins in Maine, stretches up to Canada and over to Europe, from Scandinavia to as far south as Portugal. Throughout this region, oil pollution has been the murre's worst enemy. Oil kills the birds in two ways: by poisoning them or matting their feathers so badly that they die from drowning, hypothermia or exhaustion.
Kress first came up with the idea of social attraction projects in 1977 when he used decoys to lure Atlantic puffins--another commune-bound breeder--to Maine islands the species had abandoned in the 1800s. "Decoys were long used to attract birds for hunting purposes," says Kress. "I decided to use them to lure birds into historic nesting sites instead." Eastern Egg Rock, the seven-acre island where he targeted his early work, now hosts roughly 40 breeding pairs of puffins each summer (almost all of which fledge chicks) as well as about 50 nonbreeding puffins, up from zero birds a century ago.
Photo: © COMMON MURRE PROJECT U.S. FISH AND WILDLIFE SERVICE
LURED BACK: When an oil spill led a population of common murres to abandon California's Devil's Slide Rock, scientists tricked birds into returning with a mock murre colony of mirrors, recorded calls and wooden decoys (above).
Kress, who is a consultant to the murre project, says that it is one of the most successful social attraction experiments yet. Now in the sixth year of a ten-year plan, the project brings more murres to the rock each year. During the 2001 breeding season, 113 pairs nested on the island and 85 chicks fledged. "This was a very good year for the murres," confirms wildlife biologist and project director Mike Parker of the San Francisco Bay National Wildlife Refuge Complex. It's too early to declare victory, however. Parker is waiting to see whether chicks hatched on the rock during the past five years will return to lay the next generation of precious eggs.
Parker's work gets underway each November (while murres are out at sea catching fish and saving energy for the breeding season), when he and his colleagues load up motorized rafts with decoys, ropes, speakers, CD players, mirrors and solar panels, then surf crest the waves up to the edge of Devil's Slide Rock. Fully loaded with these makings of a mock murre colony, the biologists use rock-climbing equipment to scale the island's sheer, 70-foot walls. Over the course of one day on the guano-slick rock surface, they secure all the decoys--placing them in dense clusters, which attract the most live murres. The wooden birds are surprisingly realistic, at least to humans. Viewed through a powerful spotting scope, what appears to be a decoy may suddenly flap its wings and shake its head. As for the murres' reactions, they don't fight or try to mate with the decoys, but they do preen them.
Just before leaving the island, the biologists switch on the raucous murre music, which advertises the big bash to birds from miles around. To make the tape, Parker recorded a large and thriving murre colony in Farallon National Wildlife Refuge, 25 miles northwest of Devil's Slide Rock. It took him days to find the sound he suspected would lend the most authenticity to the site--the call a female murre makes when she's copulating. Asked what it sounds like, Parker hesitates, laughs, and says, "Well, to me it sounds like she's saying, 'Quit it! Quit it!'"
In a full-sized colony, such as that in the Farallones, murres breed so close together that they literally bump wings. Their azure eggs, laid in late spring, are dotted with unique patterns of brown spots, which biologists suspect allow the birds to identify their own eggs. Even before it hatches, a chick learns to recognize its parents' calls and huddles close to them as soon as it's out of the shell. In mid-summer, after several weeks on the ledge (murres don't have nests, just patches of rock that they defend as their own), the chick ker-plunks down into the water and swims with its dad out to sea, where it learns to fish before learning to fly. While murres are klutzy fliers--they flap their wings desperately and often stumble when they land--no flying bird is a more agile swimmer. Murres spend all fall and winter at sea, then rendezvous on their breeding grounds again in spring.
Though one patch of guano-gray rock may look exactly like any other to a human, murres return--or at least try to return--to the same island season after season. They even try to nest in the exact same spot on the island. Once offspring are old enough to mate (at about four to six years), they, too, will likely homestead as close as possible to where they hatched. Because some Devil's Slide Rock residents had survived the 1986 oil spill, Parker and his colleagues figured correctly that the species' long-term loyalty to a particular site would help to reestablish the colony.
Biologists working on other social attraction experiments have not had that advantage. In projects in Maine, Quebec and Hawaii, for example, birds were eradicated so long ago that no survivors could possibly return. In such cases, success depends on a handful of bold individuals found in every seabird population. Rather than returning to their hatching place, these birds may take a chance on a new breeding site. And seeing their peers--even straitlaced, wooden peers--gives these pioneers even more confidence to brave the new world. In Maine the strategy has worked well. Lured by decoys, both puffins and terns have now colonized seven new islands off the state's coast.
Social attraction projects, if the public hears about them at all, are usually considered good-news stories. Yet the most spectacular success to date, which relocated the world's largest colony of Caspian terns, generated local and even national controversy. That's because the project used, in addition to decoys and mood music to attract birds to a new site, fences and streamers to discourage them from staying put.
Photo: © MICHAEL WILHELM
TERN-ED AWAY: The world's largest colony of Caspian terns used to breed on Rice Island in Oregon's Columbia River. But when the terns' appetite for salmon got them in trouble, scientists used decoys and other methods to attract the colony to a new breeding site: East Sand Island, where both adults and chicks (above) are now thriving.
The terns, acrobatic white birds with sporty black caps and carrotlike bills, had been living on Rice Island, a pile of dredge spoil 21 miles up from the mouth the Columbia River in Oregon. It was a spot that hatchery-raised salmon smolts also favored. Taking advantage of this windfall, the island's terns consumed more than 10 million young salmon a year--between 75 percent and 90 percent of their diet. Responding to concerns from the National Marine Fisheries Service, the U.S. Army Corps of Engineers launched a plan to nudge the terns downriver, where food other than young salmon abounded.
To beckon the terns to their new home, a team led by biologists Dan Roby of the USGS-Oregon Cooperative Fish and Wildlife Research Unit and Ken Collis of the Columbia River Inter-Tribal Fish Commission set up decoys and speakers on East Sand Island 16 miles downriver. Then they made Rice Island less hospitable by placing three-foot-tall, black mesh fences and wires with streamers across the colony site. Caspian terns, which normally nest in shallow hollows in loose sand, are "used to bare open sand with a good view in all directions," says Roby. "Suddenly, they couldn't see for more than 15 feet." Originally, the plan also called for hazing--sending people and dogs roaming throughout the colony late at night. But a lawsuit brought by a coalition of conservation groups halted the scheme at the last minute.
Fortunately for the terns, the strategy worked even without hazing. Last year, the project's third season, 9,100 breeding pairs of Caspian terns nested on East Sand Island, and none nested on Rice Island. The transferred birds have a more varied diet than they did on Rice Island--they eat herring, anchovies, sardines and other marine fish at the new site, and salmon smolt now make up just 33 percent of their diet. The terns are thriving in their new home. "I've never seen productivity like this before," says Roby. "We're going to have a bumper crop of chicks this year."
Though the murre project hasn't drawn a comparable number of birds so far, early evaluations of the effort dub it a success. More birds come to gawk at the mock colony on Devil's Slide Rock every year, and Parker is now a proud godfather to a total of 234 chicks that have successfully fledged on the rock over the past five years. Those that survive to adulthood are almost certain to breed on the island and raise the next generation of returnees--even if the decoys have been removed.
Still, Parker points out that even after five years of intensive work, only about 200 birds are spending the breeding season on the island. Before the spill, at least 3,000 bred there. "It takes no time to destroy a colony and forever for it to recover," says Parker. And despite limited success at Devil's Slide Rock, and more dramatic results in Maine and Oregon, Kress warns that social attraction--or any other type of restoration effort--can be tricky. Each must be carefully tailored to a species' needs as well as to the local ecology, he says. "Clearly, these projects shouldn't be seen as easy fixes for reckless behavior."
An avid birder, Laura Helmuth is a news editor for Science magazine in Washington, D.C.