| The Magazine of the CALIFORNIA ACADEMY OF SCIENCES |
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features On the Farallones When you're clinging to a cargo net 40 feet above the frigid Gulf of the Farallones, sharks spring easily to mind. The waters around Southeast Farallon Island, on which I'm about to alight, are a prime feeding ground for great white sharks, which feast every fall on the resident seals and sea lions. But on this warm summer day, I prefer to ignore the fact that more white shark attacks have been witnessed here than anywhere else. Besides, I've come to the Farallones not so much for sharks or seals as for the birds. Just 27 miles due west of the Golden Gate, and though technically part of the city of San Francisco, the Farallon Islands seem a world away from the city by the Bay. Few San Franciscans know much about them, but these islands, now encompassing the Farallon National Wildlife Refuge, harbor the biggest seabird nesting colony in the lower 48 states, about 150,000 birds strong and representing twelve species. The largest known population of ashy storm-petrels, and half of the world's Brandt's cormorants and western gulls, live and breed here. Though relatively remote, the Farallones are not removed from human influence. Since April 1968, the Point Reyes Bird Observatory (PRBO), under agreement with the U.S. Fish and Wildlife Service, has kept constant vigil on the granite crags of Southeast Farallon. Besides being watchful eyes ensuring that the refuge is not violated, PRBO biologists have amassed the longest-running seabird community study in North America. Seabird nesting season lasts from March through August, with the species arriving on different dates and staying for various lengths of time. (The total migrant bird tally, seabirds and all, now numbers 380 species that have spent some amount of time--by choice or by accident--on this 100-acre rock, including such oddities as a burrowing owl and a very wayward brown booby.) As soon as the Blitzen, part of the volunteer Farallon Patrol fleet that ferries food, supplies, and scientists to and from the islands, stills her engine and gets tied to a buoy off the east side of the island, the cry of gulls and the acrid stench of guano fill the air. I point my binoculars toward Great Murre Cave, a giant football-shaped opening in the rock, inside which I can make out the black-and-white bodies of hundreds of common murres dotting the wall. A boat pulls alongside the stern to shuttle us closer to shore, where a blue crane lowers the Billy Pugh--a conical net attached to an orange ring like a giant's life preserver. Four at a time, we step from the bobbing Boston whaler to the ring, grip the net, and get lifted to the landing. Although some of the resident biologists have a tradition of "Pugh jumping" into the ocean, I'm told that no one has ever fallen off unintentionally. Around much of the island steep cliffs drop straight to the water, so this is the main--often the only--way for people to land here, which helps enforce the strictly regulated access.
I have to keep looking down at the narrow path to avoid stepping on nests. Each one contains from one to three mottled green-brown gull eggs, or where the eggs have already hatched, downy gray chicks, their heads spotted black. Here is a large part of the world's largest colony of western gulls (Larus occidentalis)--25,000 birds and growing, albeit considerably less so than in the 1970s. The rich food resources just offshore prompt the island's gulls to nest in unusually high densities, and they remain here for much of the year. Although my superficial impressions are of abundance and fecundity, it's actually been a poor year for these birds. Several dead gulls are scattered beside the path, their wings angled awkwardly in rigor mortis, victims of a recent outbreak of avian botulism. So far this year chick mortality levels have hit 60 percent. Most of the eggs I have seen are a mating pair's second attempt to reproduce successfully. "This is about as bleak as I've ever seen it in terms of gull reproduction," says Sydeman. Apparently, their preferred prey fish is particularly scarce near the islands. Gull productivity has been poor for the past seven years, but so far the small number of successful pairs are maintaining the population. Later in the morning we encounter a gull wearing a yellow ankle band. Sydeman immediately recognizes this 25-year-old male as the world's oldest known western gull, born and banded in 1971. Over the years tens of thousands of breeding auklets, cormorants, gulls, and murres have been banded by PRBO biologists, who then obtain detailed life-history information about the individuals. By collecting and analyzing such data, the researchers are developing a means to determine whether populations are growing, shrinking, or holding steady, whether such changes can be linked to external influences in the marine ecosystem, and how best to ensure the birds' survival long into the future. Another dehydrated gull up ahead lies on its belly with its feet sticking straight backwards and jerkily flails its head. "He'll be dead in four to five hours," says Sydeman. He and the other PRBO staff can only watch and record how wildlife responds to the different challenges. Maintaining a full-time presence on the island costs about a quarter million dollars per year; the Fish and Wildlife Service provides $70,000 and PRBO raises the rest. At any time, from five to eight biologists and students live on Southeast Farallon in a pair of four- bedroom houses built in the 1870s for the former lighthouse keepers and their families. Juggling as many as 20 simultaneous research projects, they stay for six to ten weeks and serve as the day-to-day stewards of the islands, keeping close watch on the birds, seals, sharks, and whales. They have gathered an impressive range of long-term baseline information, and for a budding biologist, a stint on the Farallones is seen as great training that opens doors to future field work.
Auklet chicks take about 40 days, a relatively long time, to fledge from their burrows. PRBO has pioneered the use of nest boxes to mimic the natural conditions of a burrow as a way to more easily study these otherwise seagoing species. By inserting a fiberoptic scope directly into a burrow, biologists can obtain a still or video image and determine whether the nest is occupied. Birds as well as biologists appear to prefer the boxes: The 500 nest boxes established for Cassin's auklet have an 80-percent occupancy rate, higher than that of the natural burrows where numbers have been dropping. A nearby area that more than 20 years ago was so full of burrows it was dubbed the "auklet minefield" is devoid of nesting birds. Between 40,000-50,000 Cassin's auklets now reside on the Farallones, making them the second most abundant seabird here, after their larger cousin the common murre, but their population has halved in the last 20 years. So this nesting technique, developed initially to ease the biologists' work, may end up helping to conserve this and other species. Rounding a bend in the path we come to an overlook above Sea Lion Cove, where three young male Steller's sea lions cavort in a calm pool dubbed the Emperor's Bathtub, and several California sea lions roughhouse in the surf nearby. Steller's sea lions (Eumetopias jubatus) have been declining throughout their range, and are currently listed as threatened by the federal Endangered Species Act. The Farallones population presently numbers about 120, but that includes only five to ten pups. High levels of mercury, copper, and selenium may be impairing their ability to reproduce or making them more susceptible to disease. Meanwhile during the past two decades, other pinnipeds, California sea lions, harbor seals, and northern elephant seals, have been increasing at the Farallones. But the seabirds do not echo such encouraging signs. According to Sydeman, numbers of most species here have fallen by half in the last 20 years: besides Cassin's auklets, sharp declines of common murres, Brandt's and pelagic cormorants, and pigeon guillemots have been recorded. Chronic oil pollution claims a certain number of birds each year. One source is the barge Puerto Rican, which sank offshore in 1984. When it shifts on the bottom during winter storms it releases oil still trapped in its hull. Catastrophic oil spills, such as 1986's Apex Houston accident, also take their toll. Sydeman suspects, however, that many population declines are connected to natural, long-term cycles of ocean productivity around the islands. From their three decades of observations, PRBO researchers know that water temperatures have increased by about 2 degrees C overall at the islands since the late 1970s. Over a similar period, upwelling of nutrient-rich cold water appears to have dropped off. No one knows exactly why this pattern has emerged, but it could be tied to decades-long swings in marine climate. Ocean temperatures measured for the past century from southern California by scientists at Scripps Institution of Oceanography reveal interdecadal shifts between periods of warm and cold water, but PRBO's longstanding record of data is not yet complete enough to pinpoint the existence or duration of a cycle at the Farallones. "Hopefully," says Sydeman, "we'll be here another 25 years so we can say something about this." A change in water temperature and upwelling alters the sort of prey available to fish and birds. A subtle shift upward of a degree or two reverberates throughout the entire marine ecosystem. In southern California, increased sea surface temperature has been linked to an 80-percent decline from 1951 to 1993 in the abundance of zooplankton carried by the California Current. At the Farallones, which lie just east of the current and downstream from one of its richest upwelling spots (offshore from the Point Reyes peninsula), changes in the coastal food web have forced some seabirds to find new sources of food. Common murres used to feed their chicks mostly short-belly rockfish, but turned to anchovy and sardine after rockfish became scarce. Cassin's auklets now feed on a type of zooplankton that has moved in from southern California. Other species are less adept at switching diet. Pigeon guillemots only forage close to the islands in relatively shallow water, so the absence of their normal rockfish prey makes them more vulnerable to reproductive failure or other problems. Seabirds provide a "top-down" perspective on the local health of the sea, says Sydeman, and therefore should be integrated into studying how the California Current ecosystem changes. "The ecology of seabirds," he says "is how they interact with the ocean."
The cove at North Landing is the only other place where boats can access Southeast Farallon. From here the island's landmark rock formations can be viewed in panoramic succession: Finger Rock, Arch Rock, Chocolate Chip, and Sugar Loaf. Thousands of common murres breed on the back sides of these rocks, including several hundred just on tiny Chocolate Chip. North Landing's proximity to sensitive nesting colonies, which even the biologists refrain from entering, means that it is rarely used for unloading people or supplies. The remnants of a rock wall nearby attest that this was not always the case. The wall was part of an egg house, built sometime last century to store the prodigious product of the island's murre colonies. In his recent book, The Farallon Islands: Sentinels of the Golden Gate, Peter White relates the history of egg collecting. Russian explorers from Fort Ross first harvested Farallon seabird eggs. Then in 1849, a half dozen men landed and declared their inalienable and exclusive right to gather murre eggs, twice as big as chicken eggs and reportedly just as tasty. They formed the Pacific Egg Company and set to work. Eggers, pursued by hordes of gulls eager for a share of the spoils, scaled cliffs within the murre colonies and stuffed eggs into slit shirts made from inverted flour sacks. Thousands of eggs were gathered each year to satiate San Franciscans. In 1854, reports White, 500,000 murre eggs were plundered in just two months. Over a span of 45 years, an estimated 14 million eggs were shipped off the islands. Around the turn of the century, pressure from the California Academy of Sciences and the American Ornithological Union finally halted commercial egg collecting, but poaching continued for decades. Today, some 75,000 common murres (Uria aalge) live on the Farallones, far fewer than the peak of nearly half a million but still among the largest colonies south of Alaska. The parenting pair shares brooding duty for their single egg as well as the task of feeding the chick until it fledges. After fledging, the male takes its progeny to sea for two months to teach it the ways of murre life. As we continue toward Lighthouse Hill, gulls perched nearby unite in territorial cries or strafe just overhead. I stop briefly to photograph a nest, and an airborne gull deposits a guano calling card on my chest. Between the scattered nests and stray feathers, the ground is covered with bird bones bleached white by the sun. I assume that these are gull remains until Sydeman identifies them as the remains of gull meals: pieces of chicken and turkey carried here from mainland dumps and piers. "The last thing we need to do is to feed gulls on the mainland," stresses Sydeman, "but it's hard to get the message out." Gulls resort to eating garbage when fish become scarce, but the poorer quality of this food and the greater distance that parents must cover to obtain it reduce the odds that chicks will survive. Near the base of the steep path that switchbacks nearly 350 feet up to the lighthouse at the summit, a gull brooding a single egg opens its bill wide and lunges at each passing ankle. Just below the summit, numbers painted on the rocks identify monitored nest sites of pigeon guillemots (Cepphus columba). One of the birds, all sooty black except for a fire-engine red bill, mouth lining, and webbed feet, stands outside its nest as we pass. Come winter it will migrate north, perhaps as far as British Columbia. Sydeman stops to retrieve the stiff, mangled carcass of an ashy storm-petrel (Oceanodroma homochroa), killed by a western gull. The carcass retains the living bird's musky odor, a smell that helps researchers locate active burrows by bending over to sniff the rocks. Sydeman will add this specimen to others that are part of a population viability and mortality study that he is conducting with PRBO's population ecologist Nadav Nur and Farallon biologist Michelle Hester. Since 1994, they have been collecting and counting discarded storm-petrel wings and comparing the figure with the known population size for this slope below the lighthouse. Then they can estimate the extent of storm-petrel deaths due to gulls. A few months after my visit, Sydeman reports preliminary results showing that gulls kill about 2.5 percent of the island's storm- petrels each year. The absolute number of predated birds may be small, but the Farallones harbor up to 80 percent of the world's ashy storm-petrels, and their numbers here have been dropping. Cassin's auklets also find themselves on the gulls' list of prey. A computer model suggests that if gull predation were eliminated, the storm-petrel population would soon become stable. Otherwise, it could approach extinction in a few decades. How should the problem be negotiated when both predator and prey are protected? Sydeman wants to explore non-lethal options first, such as repelling gulls from sensitive storm-petrel nesting areas by playing a taped gull distress call or establishing new storm-petrel nest sites away from congregating gulls. The Fish and Wildlife Service and PRBO will soon be discussing possible strategies. The Biological Resources Division of the U.S. Geological Survey (formerly the National Biological Service) has funded PRBO to investigate the health of storm-petrels at the Farallones and at the Channel Islands and to determine the genetic distinctiveness of each population. No one knows whether northern and southern storm-petrals remain isolated from year to year or intermingle. From the U.S. Coast Guard's solar-powered light atop Lighthouse Hill we look eastward across a colony of ten thousand murres below. Midway along the top of a saddle-shaped ridge above Shubrick Point stands a precariously positioned blind that scientists scramble to in order to observe these murres and another colony of equal size on the other side. In the distance the peak of Mount Tamalpais on the mainland juts above a dense band of fog. Behind us is West End Island, cut off from Southeast Farallon by a narrow surge channel. West End, dominated by a promontory called Main Top where numerous murres and cormorants nest, has been designated a special wilderness area within the refuge--off-limits to any visitors, including researchers, except to count elephant seals during winter. Last August, biologists spotted a bull northern fur seal with three females and a single pup on West End. The pup is the first of this species to be born at the Farallones since 1817. The sighting raises hope that northern fur seals (Callorhinus ursinus) may expand their range from a single California breeding colony on San Miguel Island to reclaim the Farallones. My landing permit does not allow for an overnight stay, and anyway the next boat will not arrive for another week. With a three-hour return sail ahead of us, the time soon comes to reassemble at East Landing, cling again to the Billy Pugh, and be shuttled offshore to reboard Blitzen. Captain Dick Spight circumnavigates Southeast Farallon and West End before heading back toward San Francisco. From the upper deck, I watch rhinoceros auklets and murres flying in the opposite direction, skimming the ocean surface, wings flapping wildly. Anchovies draped from their bills shimmer in the sun as the birds return to the island. Blake Edgar is an Associate Editor of California Wild. |
Spring 1997
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