The woman cowers inside a phone booth as a fury of birds tears through town. Demented seabirds hurl themselves at the windows, cracking the glass. Outside, beaks and claws swirl over bloody bodies in the streets.
This famous avian attack on a California seaside town is fictional: a scene from Alfred Hitchcock’s 1963 horror classic The Birds. But the winged tornado was inspired by a real incident in August, 1961, when thousands of deranged sooty shearwaters flew into buildings and crashed in the streets of Monterey Bay towns near Hitchcock’s home. They probably had been poisoned by domoic acid: a potent, brain-scrambling toxin produced by algae bingeing on sewage and fertilizer runoff.
Domoic acid poisoning is just one of many environmental perils that sooty shearwaters encounter on their annual migration, which is among the longest on Earth. In their quest for endless summer, they are tour guides of the ocean hazards that are driving nearly half of the world’s seabird species into decline.
Named for their low, rocking glide with wings seeming to slice the sea, sooties rack up nearly 40,000 miles a year, flying from nesting colonies near New Zealand and Chile to fishing grounds as far north as Kamchatka, looping a giant figure 8 over the Pacific. Every spring and fall, they make their grueling, month-long journey, flying as much as 550 miles a day, much of it without stopping to eat.
Right around now, flocks of sooties are finishing up their summer vacations feasting in the rich, upwelling currents of the Northern Pacific and are heading south to breed. En route, they’ll run a gauntlet of manmade obstacles in the ocean: fisheries that deplete their prey and snare them with hooks and long lines, drifting continents of trash and noxious industrial spume. Crossing major shipping lanes, they risk getting slimed by oily bilge and clobbered by vessels. Their meals of anchovies and sardines are tinged with contaminants. To top it off, climate change brings warming waters and scrambled wind patterns that can leave them starving.
When they finally reach their breeding grounds in the southern hemisphere, rats and other foreign predators invade their burrows and kill their defenseless chicks. The parents unwittingly feed their chicks plastic. And on top of all that, sooties are a traditional food in New Zealand, where hunters kill hundreds of thousands every year.
Little wonder that these long-distance pilgrims, second only to the Arctic tern, are increasingly failing to survive their journey. Although they are one of the world’s most populous seabirds, sooty shearwaters are now classified as near-threatened because of steep declines.
These hardy mariners spend most of their lives at sea, coming ashore only to breed. In California waters, the birds tend to forage several miles off the coast. But on late afternoons they often gather nearshore and herd their prey into the shallows, treating places like Monterey Bay to a dazzling, choreographed aerial ballet.
But the sooty dance corps is shrinking.
“We used to see so many sooty shearwaters they would just literally blacken the horizon,” said naturalist Debi Shearwater [no relation to the bird], who has led seabird-watching trips along the California coast for four decades. “At one time, I counted a flock of 800,000 from the beach. And a larger flock than that beyond them, which I couldn’t count. We’re not seeing anything like that anymore.”
In Southern California, populations dropped as much as 90 percent between 1987 and 1995, and more recent observations off Central California show numbers are generally lower. In the Southern Hemisphere, burrow counts at a large New Zealand breeding colony measured a 37 percent drop between 1969 and 1996, a slide that appears to be ongoing.
“Seabirds get the brunt of a lot of human activities,” said Hannah Nevins, seabird program director for the American Bird Conservancy. “They’re the interface, squeezed against the coast on one side and human populations on the other.”
The marathon begins
As it wings south when fall sets in, a sooty shearwater already has endured an array of challenges during its May-to-September northern sojourn, according to mapping by Scott Shaffer, a San Jose State University wildlife biologist who has tracked the species’ travels over the Pacific with geolocator tags.
Some cruised the currents north and east of Japan. Here, they may have run into oil leaked by rigs off Russia’s Kamchatka Peninsula and foraged in a food web laced with dioxins and organochlorines spewed by industry. Others gathered near the Aleutian Islands and the Gulf of Alaska. While food is plentiful there, so are fishing longlines, and sooties are irresistibly drawn to the thousands of baited hooks trailing for miles over the sea. They get hooked or tangled in the lines, and drown.
The rest fished the waters off North America’s West Coast. Teeming with their favorite prey – anchovies, squid and sardines – this region, called the California Current, hosts an estimated 7 million sooties, roughly one-third of the world population. They mass in several “habitat hotspots” along the continental shelf, including Washington’s Columbia River outlet and California’s Monterey Bay, according to satellite tracking by Josh Adams, a research biologist with the U.S. Geological Survey in Santa Cruz.
Like the birds that inspired Hitchcock, sooties summering near West Coast cities are in danger of domoic acid poisoning. Urban runoff that contains urea, a nutrient from sewage and fertilizers, can turn the normally benign diatom Pseudo-nitzschia australis into domoic acid factories. The neurotoxin makes its way up the food web, causing disorientation and erratic behavior in birds and sea mammals.
“It’s a definite concern,” causing “a significant effect of wildlife mortality each year,” said Raphael Kudela, a University of California, Santa Cruz ocean scientist who studies harmful algal blooms.
Kudela suspects that the 1961 frenzy of poisoned sooty shearwaters was spurred in part by leaky septic tanks installed in booming developments around Monterey Bay. Today, sooties dining in the California Current may be even more at risk from toxic outbreaks.
“We’ve seen a lot more problems in addition to pseudo-nitszchia, new harmful algal blooms showing up along the West Coast of California, Oregon, Washington that haven’t been there before,” Kudela said. Climate change seems to be at fault, stretching the season and region where the algae blooms occur.
Domoic acid outbreaks also have climbed over the past two decades as urea loads in rivers and bays rise. “This year’s been particularly bad,” Kudela said, “we’ve seen really high levels of toxicity.” Scientists aren’t exactly sure why, but one reason may be that warming offshore waters drive sea lions to shore, concentrating their waste in pools that turn algae toxic.
Because sooties are only part-time California residents, their health is not closely monitored. But marine rehabilitation volunteers have seen a steady stream of California sea lions poisoned with with domoic acid. “So we know it’s getting in the food web and it’s having an impact,” Kudela said.
While foraging in the California Current, the sooty also may have encountered oil leaked from ships and natural underground sources. The problem is chronic and low-level, according to Nevins. She found oil on about 3 percent of the birds she necropsied at a Santa Cruz veterinary center. Yet major spills are a threat, too: the 1998 Command oil spill off the California coast killed as many as 29,000 sooty shearwaters.
Piling on the problems, the seabirds risk collisions with container ships headed to some of the world’s busiest ports. Fishing industries vacuum up their prey for uses such as chicken feed and fertilizer. Even worse, a sooty might mistake the garbage floating in these waters for food, which can block its digestive tract, puncture its intestines and release toxics into its systems. Nevins finds plastics in 70 to 80 percent of the sooty shearwaters she examines.
And nearer shore, these birds encounter mercury, agricultural runoff and other pollution in parts of their range. Based on studies of other birds and marine life, seabirds are likely to suffer effects of fat-stored chemical pollutants during their long migrations.
All of these stressors add up, said Sara Maxwell, a postdoctoral scholar at Stanford University’s Hopkins Marine Station in Monterey Bay who mapped cumulative human impacts on sooties and other marine predators. Effects from one hazardous encounter can make birds more vulnerable to others, she said.
Amidst all this, “they have to build up enough fat to be able to migrate back,” Shaffer said. Rising temperatures and acidification are making oceans less productive; extreme weather events can make it even harder to feed. While the sooties seem to be heading out with full tanks this year – at least no major catastrophes were seen – they’re not always so lucky.
“You can imagine if they make this migration all the way up here and conditions are poor,” Shaffer said. “They’re going to have to tough it out.”
Headed south: giant garbage patches
By next week, most sooty shearwaters will be on their way to their breeding colonies in the Southern Hemisphere. Birds dispersed across the North Pacific, off Japan, Russia, Alaska and California, meet up around Hawaii for the push across the equator.
Their itinerary takes them through a junction of currents and winds that amasses flotsam across a wide ocean swath near Hawaii. Most of it is plastic: a raft of buoyant and indestructible particles including nearly invisible microplastics, bead-sized industrial pellets, chunks of foam, rigid shards and a variety of objects like pen caps and shiny balloon strips that resemble their prey.
“Plastics were created during World War II basically as a really great polymer that was easy and disposable. And everything that we’ve thrown into the environment since World War II is still there,” said Jennifer Provencher, a Ph.D student at Carleton University in Ottawa, Canada, who studies seabirds’ plastics ingestion.
While the eastern North Pacific gyre, the so-called giant garbage patch, probably is the most extensive and well-known marine trash field, the problem is ubiquitous in all oceans. Plastics sponge up organic pollutants such as polychlorinated biphenyls (PCBs) and toxic metals like cadmium, chromium and lead, concentrating them up to a thousandfold.
These contaminants then leach into the animals that eat them. In addition, these plastics are manufactured with chemicals such as plasticizers and flame retardants that mimic hormones and could alter developing brains and reduce fertility.
Some of these chemicals, in experiments with other animals, impair processes that would be key to migration, including learning, memory and feather growth. “Even low levels of a number of toxicants have been shown to interfere with memory and learning in humans, which suggests that these toxicants may have particular relevance for migratory birds that rely heavily on neurosensory mechanisms to navigate between the various sites along their route,” a team of Australian and Dutch scientists wrote.
Researchers are now investigating how much of these substances enter seabirds’ systems. They likely get big doses when contaminants in their fat stores are released during long migrations.
“They’re a long-lived species and so these low-level exposures that could affect them over time could have ramifications for the birds’ health,” said Myra Finkelstein, a UC Santa Cruz wildlife toxicologist participating in an international study. “It’s important to understand the long-term consequences of all this plastic our marine species are ingesting.”
Ships on the high seas pose another danger to the migrating sooties. At night, powerful beacons from cargo and cruise ships sweep the water. Drawn to the light, the birds can be struck and injured, or killed. And by day, lethal bait on fishing longlines once again beckons.
At the Equator: an arduous crossing
At mid-month, sooties will cross the equator in a mad, 10-day dash across the Pacific that pushes their bodies to the limit.
From 30 degrees north to 30 degrees south – 3,600 nautical miles – they speed up to more than 500 miles per day and fly straight through, barely stopping to feed.
Shaffer’s tracking study shows almost no diving activity here, indicating that warm waters hold little for them to eat.”They’re trying to get over it as quickly as they can to get to where resources are much better,” he said.
Migration is a formidable physical challenge for all birds, with severe metabolic and navigational demands. Ultra-marathoners like sooty shearwaters require a precision balance between fuel reserves and food stops, with little margin for detours or delays.
“If the winds they use to travel hit a lull, they might be stranded for days,” Shaffer said, resulting in off-schedule or missed breeding, or even starvation.
Finally home: imported predators
About four weeks from now, in early November, sooty shearwaters will have reached their southern destination. Couples that went separate ways up north find each other and reunite, while singles court with duet calls and gentle nibbling. Once bonded, they typically mate for life.
Nesting mainly on islands off New Zealand, with a few small colonies in Australia, Chile and Argentina, the couples dig burrows several feet deep and raise their solitary chick underground. The parents travel nearly 1,600 miles from their nests to forage for fish and krill at the edge of polar waters, leaving their young for as long as two weeks.
Staying home alone is normally no problem for young birds in these predator-free havens. But in recent years, foreign invaders have hitchhiked here along with humans. Major sooty colonies south of New Zealand were nearly wiped out after a ship-borne “rat spill” released a scourge that devoured eggs and chicks. In 2008, working with the nonprofit group Oikonos Ecosystem Knowledge, Nevins and colleagues eradicated the rats and set up a quarantine program to prevent reinfestation. Now rat-free, the colonies are coming back to life. Still, throughout the region, predators stowed away on fishing boats, helicopters or ships are an ever-present threat.
“Rodents, cats and stoats all continue to be problems for sooties,” Nevins said. New Zealand has no native mammals except for bats, and birds on these islands lack defenses to escape such “exotic pests.”
Here too, plastic pollution abounds. “Marine litter on beaches is a global problem,” Nevins said, “and even in New Zealand you can see plastic garbage from both land-based and sea-drifted sources.”
In colonies studied off Australia, human litter, most of it plastics, was found in 63 percent of adult short-tailed shearwaters, a closely-related species. “I think one of the most shocking for me was an entire glowstick, still bright red/pink,” said Denise Hardesty, an ecologist with the Commonwealth Scientific and Industrial Research Organization in Tasmania who worked on the research.
Sooty shearwaters also likely feed plastics to their chicks. “You can see small bits of colorful plastics on the floor of the nest burrow,” Nevins said. In Hardesty’s study, 85 percent of young short-tailed shearwaters had eaten plastics, while another recent report found bits of plastic in every fledgling examined.
And a study of flesh-footed shearwaters in Australia found that plastic consumption appeared to stunt birds’ growth and release health-endangering levels of a toxic metal, chromium.
“We’re starting to see more and more that plastic ingestions can have effects on individuals and maybe even populations,” said study co-author Alex Bond, a conservation scientist with England’s Royal Society for the Protection of Birds.
In April and May, when the chicks are nearly grown and getting ready to leave their nests, a practice known as “muttonbirding,” brings further danger to sooties and other young shearwaters around Australia and New Zealand. Prized for their rich, tender meat and high fat content, the young birds are snatched from their burrows or grabbed when they emerge at night to exercise their developing wings. In the past, hunters took huge numbers of chicks. Regulations now limit muttonbirding to an estimated 400,000 catches a year but an untold amount of poaching still threatens.
By May, most sooties are hitting the road again. Their exodus is staggered, depending on whether they have young to tend, and when the chicks are ready to go off on their own.
On departure, they’ll first head east, with some flying as far as South America, where they may encounter oil or become tangled in fishing gear. Pollution, including unregulated agricultural runoff, threatens them there, and harvesting of fish makes for scarce prey in some places.
Sooties then swing northwest and make their way back for another boreal summer, through another garbage gyre, another equator crossing, another marathon tour of our oceans’ hazards.
Connecting the threats
Sentinels of ocean health, seabirds are the most rapidly declining birds on the planet, and the odyssey of the sooty shearwater highlights many of the obstacles they face.
Most pop up in multiple legs of their journey, and some – like plastics – are encountered everywhere. While about 90 percent of sooties migrate over the Pacific, smaller numbers travel along the U.S. East Coast, flying from the Falkland Islands and Chile to the coast of Nova Scotia, where they face these same problems. A study by Provencher found plastics in more than 70 percent of sooty and great shearwaters off Northeastern Canada.
“Human waste in general is making its way into wildlife,” she said.
The biggest threat to birds is the wild card played by climate-altering carbon dioxide emissions, which reached a new record high this year. Changing conditions can turn a chain of non-lethal impacts into a deadly event for a seabird.
“Maybe the prey base is not as strong as in previous years due to climate change. A seabird hasn’t had the foraging it normally does,” said Maxwell, giving an example of how effects interact and add up.
“Then you bring in some pollutants that are accumulating in the body and run the bird down… So if the animal’s already not at its highest level of fitness and then it gets caught on a fishing line, on another day it might be able to recover from that. But because of other cumulative impacts, the fitness is actually quite reduced, so now it ends up dying on the fishing line.”
Sooty shearwaters’ perilous path illustrates how a phalanx of threats connect up in the oceans.
As tour guides to a troubled environment, their lesson is “really important for linking us humans,” Nevins said, “and understanding how it’s not just a little bit of plastic here and a little oil there. It’s the combined impacts of all of our activities.”