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The Salt Pond Puzzle: Restoring South San Francisco Bay



We were on patrol. Caitlin Robinson-Nilsen, a young biologist in shades and a ponytail, steered the 4WD Explorer along a muddy levee in Fremont, Calif., and I rode shotgun, staying vigilant. She surveys snowy plovers –– adorable, six-inch, two-ounce, skittering shorebirds, with black collars and eye-patches –– as the waterbird program director for the San Francisco Bay Bird Observatory. But we weren't after plovers that April day last spring. We were cruising the South Bay's vast salt pond system in search of something larger, more dangerous. Through the windshield was a strange land of water and sky, rimmed with office parks. They're out there. They'll steal your lunch.

We were looking for California gulls. Trash birds, some say -- but that's only a partial description of their diet. They also adeptly hunt and devour the eggs and chicks of waterbirds like plovers -- many with a tenuous hold on disappearing habitat. Now, on the metropolis' coattails, the Bay's California gull population is going gangbusters. To make matters worse, 23,000 of them -- roughly half the Bay's population -- were displaced from their nesting grounds when the levees of A6, a 330-acre salt pond, were breached in 2010, returning it to the tides as part of the South Bay Salt Pond Restoration Project.

The gulls were on the loose, hunting for new homes, and no one, least of all Robinson-Nilsen, wanted them settling near plovers. It was one of many unintended consequences of the largest wetlands restoration on the West Coast. Break down one barrier, others are likely to crumble. Restoration is seldom as simple as banishing exotics and promoting natives; it's a series of trade-offs, and the odds are that not every species will come out ahead. Nor is it easy to delineate which species actually belong in an ecosystem as radically transformed by people and invasive species as the South Bay. Still, this restoration, like most, is optimistic: It hopes we can all be winners.

Gulls are good at winning, and well-suited to human sprawl; snowy plovers, not so much. Charadrius nivosus is an undeniably endearing bird, found all over the world. But it's a nervous soul, unsettled by tall structures. Telephone poles? As scary as hills. Their subtle nest scrapes and camouflaged eggs are found only on beaches, gravel river bars and sand and salt flats, right where humans like to build high-rises and vacation homes, walk dogs and drive ATVs, activities that can disturb or destroy nests. As if that weren't enough, snowies also have to contend with European beachgrass and climate change swallowing up shoreline nesting grounds. And now, an explosion of gulls.

Two subspecies of snowies exist in North America, the Cuban along the Gulf Coast, and the western, which consists of distinct inland and coastal populations. The latter -- Robinson-Nilsen's charge -- ranges from southern Washington to the tip of Baja, but most reside in the Bay Area and southward. In 1978, both the inland and coastal western snowies became species of special concern in California, but only the coastal birds were listed as threatened under the Endangered Species Act, in 1993.

The first statewide survey between 1977 and 1980 found snowies missing from 33 of 53 known coastal breeding locations. In the Bay Area, 351 birds were counted. By 1991, there were only 176. The low -- 72 -- came in 2003. Since then, the numbers rose to about 250. But this year, just 147 were spotted. The Bay Area is thought to host 5 to 10 percent of the entire coastal breeding population, almost all of them in the salt ponds. It's primo habitat: light-colored expanses to blend in while nesting; wet edges for hunting brine flies, using the run-stop-peck approach; and blessedly few people, since it's mostly off-limits to the public.

April to May is peak migration, and western sandpipers dotted every shallows. They were innocent. We passed them by. Up to a million migrating waterbirds stop in the San Francisco Bay on their journeys to their Northern breeding grounds, but Robinson-Nilsen spends her entire field season here, turning circles. Originally from Vermont, she discovered her passion for threatened piping plovers on Long Island. She studied snowies for her master's at San Jose State, and it became her dream job: "Anything to do with nesting plovers." She listens to the wind or to NPR, seldom bored. But as we zigzagged, she confessed, "I end up talking to the birds a lot."

When we reached the levee between A22 and A23 -- A for Alviso, a marsh-side community in northern San Jose -- there they were: A flock of roosting gulls, insouciantly ruffling their feathers, and ours, in the breeze. They're pretty snowy themselves, with a black ring and red spot on their yellow bill, and a four-foot wingspan. She counted them through her open window, jotting "110" in the California gull column of her datasheet. "Quite a bit less," she said.

But even one was too many: This was one of the bird observatory's "no gull zones." Earlier in the month, an irksome 700 had loafed here, right between two ponds with a handful of nesting plovers. "We were like, 'Oh, my goodness, we'll never be able to keep them off,' " Robinson-Nilsen remembered. The bird observatory began hazing them twice daily, and when we arrived, things seemed under control. "Once they lay eggs, they're protected by the Migratory Bird Act," said Robinson-Nilsen. "So we're putting in a big effort now."

We drove onto the levee, spattered with whitewash, chicken and rib bones, like the mouth of an ogre's cave. Robinson-Nilsen pointed south. "That big 'mountain' is Newby Island Landfill," she said. "Hundreds, if not thousands, of gulls feed there everyday." To the north was another landfill, making this levee an ideal midway hangout. We parked, stared the gulls down. It wasn't high noon, but close enough. On Robinson-Nilsen's command, we swung our doors wide and sprang out. She blew a silver pea whistle bought in Chinatown, and the sound carried like a battle cry. I wielded my notebook. The gulls flinched, scattering with a few resentful mews. Small, sweet payback, I thought, for all those pilfered hotdogs.

Perhaps you've seen this place from above. Banking north toward San Francisco International Airport's tarmacs -- themselves built on former wetland -- the mosaic of rectangular and irregular ponds ringed by the South Bay's sprawl look like puzzle pieces, or strange agricultural fields. The more startling the color, the saltier the water: With evaporation, those blue-green with algae become saturated with orange brine shrimp, and later, red blooms of bacteria. Many ponds show the sinuous traces of former marsh channels.

The ponds exist because the South Bay is especially windy, which accelerates evaporation. Native Americans, the Ohlone, gathered salt for trade long before others sold it to Sierra Nevada silver mines to process ore. The first salt ponds were constructed around 1860. When all was said and dug, about 85 percent of the Bay Area's leg-swallowing wetlands were gone: filled and built upon, or in the case of the salt ponds, diked off from the tides. Just as the pond systems were designed so that increasingly saline water could be ushered toward central "crystallizer beds," ponds once owned by more than 100 small companies were eventually bought up by just one. The agribusiness giant Cargill still operates 11,000 acres here, producing 650,000 tons of salt annually -- 4 billion shakers' worth.

For decades, scientists and conservationists recognized the value of restoring tidal marsh, but only recently did a big opportunity present itself, when Cargill decided to scale back its holdings. Encouraged by local environmental groups  such as Save the Bay, Sen. Dianne Feinstein, D, stepped forward to finesse a deal. In 2003, the state, with support from federal agencies and local foundations, paid Cargill $100 million for land that included 15,100 acres of salt pond.

With that, the West's largest, most ambitious wetland restoration was born, spanning a triangle of South Bay pond complexes: the A and R ponds, owned and managed by the U.S. Fish and Wildlife Service; and the E ponds, belonging to the California Department of Fish and Game (see map below). The California Coastal Conservancy leads an impressive coalition that includes these agencies, the U.S. Army Corps of Engineers, local water and flood control districts, and supporting science organizations like the U.S. Geological Survey and the bird observatory.

The goal is to return salt pond to marsh, providing habitat for species like the endangered California clapper rail and salt marsh harvest mouse, while improving the Bay's water quality and protecting Silicon Valley's high-flown but low-lying real estate from flooding. California sea levels are predicted to lift as much as five-and-a-half feet by 2100 due to climate change, and tidal marsh is the first defense, a sponge that absorbs storm surges and slowly wrings them out.

Once rooted, marsh filters runoff and captures sediment, so to a degree, it's self-preserving, rising and falling with the ocean. But the Bay Area's severely fragmented marsh and dependent animals may not be able to keep up with rapid sea level change. Thus, the biggest restoration -- on par, in size, with the largest in the Everglades and Chesapeake Bay -- is a race against rising tides. The estimated $1 billion public-private endeavor aims to restore 5 to 10 percent of the Bay Area's wetlands in 50 years, as part of a larger push to reclaim a quarter overall. (About $600,000 of that money, though, is slated for flood control levees.)

A6 was one of the first ponds returned to the tides. Dubbed "the Duck's Head" because of its shape, the pond lacked a "water control structure" (a fancy name for a gate), and after the winter's rains, it dried to a hard, crusty pan. Protected from raccoons and coyotes by a moat-like ditch, the 23,000 nesting gulls gradually sprawled like tract housing across its salty flat. But when Robinson-Nilsen and I arrived, A6 looked like ocean. Power lines crisscrossed the horizon and the hangars of NASA's Moffett Field loomed to the west. But in the breeze, you could smell the Bay's fecundity, its ability to heal itself.

When A6 will become marsh again is anyone's guess. Once, its bottom was at sea level; now, it's six feet below. The land subsided as agriculture drew down the water table, causing deep alluvial layers to dry up and settle -- forever increasing flood risks. Alviso is especially vulnerable: Some areas are 13 feet below sea level. A devastating flood in 1983 left neighborhoods 10 feet underwater.

"A6 is an experiment," says Cheryl Strong, a wildlife biologist for the Don Edwards San Francisco Bay National Wildlife Refuge, which encompasses the A and R ponds. "It's going to take awhile before we've got enough sediment for the pond to be above the tide line. I mean, it's going to be aaawhillllle." In 2011, the breached pond collected nine inches of fresh sediment, but it may take 50 years or more for mature marsh to appear.

Robinson-Nilsen panned her Swarovski scope down a former A6 levee that the restoration project had broken apart and mounded into a dashed line of islets. In the long run, they'll provide dry, vegetative shelter for creatures during high tides. But until enough sediment settles, they'll be submerged periodically. Through the scope, they seemed bare mud, except for the marsh seeds and propagules we couldn't see -- and the thousands of gulls we could.

"There's a lot of copulating going on," Robinson-Nilsen casually reported. A gull flew overhead, hauling a stick for a nest probably destined to be flooded. By counting the birds in a single scope view, and counting the views, she estimated 3,000 gulls, just a fraction of A6's former colony. Robinson-Nilsen was glad to see them sticking it out, well clear of the snowiest spots.

You can't blame the gulls. In the web of ecology, there are many knots that are difficult to untangle. Right about when the gulls first appeared in the South Bay, something unusual happened at salty Mono Lake, clear across the state on the dry side of the Sierra Nevada. Since 1941, the city of Los Angeles had siphoned water from the lake's tributaries 350 miles south to faucets. The lake dropped 45 feet in 40 years, and in 1977, a land bridge formed between the sagebrush mainland and Mono's second largest island, Negit.

California gulls typically breed inland, from the Great Basin to Manitoba. (It's the Utah state bird, in fact, the "seagull" that saved Mormon settlers' crops from a katydid plague.) About 50,000 of them nested at Mono each year, two-thirds on Negit, feasting on brine shrimp and alkali flies before wintering on the coast. But suddenly, coyotes could stroll over to the island. The gulls abandoned ship in 1979, settling on surrounding islets, where many remain. Negit became an island again, but it's still gull-free.

Curiously, though, since then a decline of Mono's summer California gull numbers has correlated almost exactly with the rise of the South Bay colonies. In 1980, the first nests were spotted: 24 gulls, on a salt pond island. In 1982, less than 200. In 2010, 46,000. That's nearly exponential growth: the myth of the inexhaustible West played out by a bird. The population likely snowballed in the city for many reasons; you can't pin it on Negit's land bridge alone. But the parallels are striking.

Now, A6's displaced gulls also have to go somewhere. "We don't really want the gulls in the Bay," says Robinson-Nilsen, "but we don't want to force our problem on other people, like Alcatraz and the Farallones." The Farallones, a cluster of rugged islands 30 miles offshore, are known for seabird rookeries with their own slew of problems. They don't need a plague of rogue gulls. And surely researchers would haze them right back around.

If the gulls remain in the Bay, the restoration team would prefer they resettle near A6 or join another existing colony, where their impact on other species is at least known. Call it smart growth: No new sprawl, only infill. In fact, the restoration team decided not to evict one 10,000-gull colony near the plover's primary stronghold in the E ponds -- E for Eden Landing Ecological Reserve -- for fear of further upsetting the status quo. "At least they're not nesting in the middle of a plover pond," says Robinson-Nilsen.

We were now driving a nine-mile loop of levees open to joggers. In the distance, the white, upswept tents of Mountain View's Shoreline Amphitheatre -- a rock 'n' roll pavilion whose lawn seating is the flank of another landfill -- mirrored Cargill's towering salt stacks. We stopped to survey a boisterous colony of gulls that had cropped up beside A14, just east of A6 and a good distance from the "no gull zones." Robinson-Nilsen counted 4,500 gulls, up from last week's 3,000. Since there were no eggs yet, we strolled a short way into the colony. I wasn't sure if it was a wise decision. "Of course, I forgot my raincoat today, but this would be a pretty good place to wear it," said Robinson-Nilsen. The gulls rose like a handful of salt flung into the wind. They hovered in the airstream, white crosses barking down at us. We were surrounded.

At first, Robinson-Nilsen didn't care for the gulls, but now, she says, "I find them completely fascinating. They're beautiful, and very good parents. I respect that they dive-bomb us and poop on us, and hit us on the head." My jacket was Gore-Tex and hooded, but luckily it wasn't quite bombs away. The gulls were still building "nest bowls" in the humped dirt, lined with sticks, minor construction debris and decorative items from the Newby Island landfill and beyond: chicken bones, Barbie limbs, and once, said Robinson-Nilsen, a plastic French fry.

Years ago, 20,000 or 30,000 gulls were said to have gathered at Newby Island, when the winds were right. So many circled above the refuse that employees complained of vertigo. The landfills became to gulls what refrigerators are to teenage boys or the moon to tides: Of "over-riding importance (to their) movements," as Josh Ackerman, a U.S. Geological Survey biologist studying the South Bay's avocets, stilts, terns and gulls, wrote in a recent report. In 2008, Ackerman's team attached radio-transmitters to gulls, and discovered they reliably put in a long day at Newby Island, arriving fairly punctually at 6 a.m. to meet the first wave of trash, and punching the clock with the last truck at about 6 p.m.

"I'm sure it's not good for them," says Robinson-Nilsen, of the menu. "Most of it's not good for us." Good, of course, is a relative term: California gulls are one of the few birds able to raise a brood on garbage. Yet the landfills haven't taken pressure off the South Bay's waterbirds: They've established the gull's home range right where more than half of the South Bay's waterbirds nest. In 2008, gulls snatched up a gluttonous 61 percent of avocet chicks and eggs here. Of the 212 Forster's terns Ackerman's team recently radio-tagged, the gulls digested about half -- worrisome, considering the salt ponds hold a quarter of the Pacific Flyway's population

The gulls' toll on the plovers in the E ponds is unknown, but given a Bay Area population of fewer than 250, any consumption hurts. In the bird observatory's office in Milpitas, Robinson-Nilsen showed me evidence from a camera trained on plover nests: A hapless plover flushes. Ten awful seconds later, a gull lands and chokes down three supposedly camouflaged eggs so fast the footage looks accelerated.

In response, Newby Island has begun an ambitious abatement program, employing a falconer, and pyrotechnicians in fluorescent vests and hardhats who fire off "bird bombs" and "whistlers" that leave hanging spirals of smoke in the air. When I visited, hundreds of gulls landed sneakily on a ridge behind a sharpshooter. Eventually, he discovered them, turned and fired. They sprang off, like plastic shopping bags swept up in a gust.

Barriers between waste and wildlife are expensive to rebuild. This program costs several hundred thousand dollars annually. At least it works. Twice a month, Robinson-Nilsen surveys Newby Island. The flock has thinned dramatically. "If they stop eating at the landfill, then the population will decline or plateau," she says. "And if that means they turn to wild sources (of food), well, it's worth having a few tough years for our birds."

But the South Bay's avocets, stilts and snowy plovers may face an even bigger menace than California gulls: the restoration itself. Converting pond to marsh will make the ecosystem healthier overall, but reduce the birds' niches. In fact, before the salt ponds appeared with their vacant stretches, snowy plovers probably didn't nest around the Bay's rim. They were found on San Francisco's Ocean Beach, in Pacifica, and around Half-Moon Bay -- places they no longer breed because of increased human traffic. Nor were nesting avocets and terns as common bayside, since there were few sparsely vegetated islands. Forster's terns only colonized in 1948, on dredge spoil islands left in salt pond corners. Like the gulls, these birds are dependent on the mess we made.

Should we worry about gulls seizing plovers and other birds if those species didn't live here historically? "When it comes to this restoration, as far as what were baseline conditions, there really is no such thing," Josh Ackerman says. "Most people would argue that the baseline state is the present." We don't know, precisely, the ecological equation of old; even if we did, the conditions that created and sustained it are long gone, and there are responsibilities, now, to additional agencies. In other words, the very word "restoration" should be taken with a grain of salt. Those redesigning the ponds are juggling a vision of the past with today's reality -- and moving forward.

Two options have been proposed: In the minimum "50/50" scenario -- which would leave many ponds intact -- only half of the 15,100 acres would be reopened to the tides. Since 2011, 2,910 acres have been returned to the bay, about 39 percent of this goal. But restoration leaders are gunning for another vision, "90/10," wherein all but 10 percent of the salt ponds become marsh. The outcome will depend on scientific feedback -- the kind of data Ackerman and Robinson-Nilsen are collecting -- and, of course, on funding.

For the gulls, the breaching of A6 was an ecological disturbance on the order of the Mono Lake land bridge. For other waterbirds that have adopted the salt ponds as a surrogate for lost wetlands, the restoration -- without vigilant management -- could loosely resemble the disappearance of Mono's wetlands, which supported millions of birds. These events epitomize the changing times: The first of insatiable thirst, without any regard for ecology; the second of an awakened environmental consciousness, with tough choices to make. Going with 90/10 would likely end the stay of snowies in the Bay Area, says Strong, failing an official restoration goal: to "maintain current migratory bird species." Thus there are "marshistas and pondistas," Strong explains.

The arguments for more marsh are compelling, however, in terms of water quality and flood control over the long term, and from yet another avian perspective. The California clapper rail might benefit most from the 90/10 scenario. Shy, secretive and about ankle-height, it's arguably the Bay's highest-profile endemic creature, a subspecies listed as federally endangered in 1970. Its numbers climbed from a low of about 500 to a peak estimate of 1,400 in 2006. Invasive red fox control helped, and so did the spread of an East Coast cordgrass.

The U.S. Army Corps of Engineers first planted Spartina alterniflora in the '70s to stabilize Alameda flood-control channels. It hybridized with native cordgrass and infiltrated the lower marsh, where it grows so densely it shades out other flora. While native cordgrass sticks to channel edges on the Bay's upper marsh, the super-vigorous mongrel chokes waterways and flood-control channels. The invasive spreads across the mudflats, reducing the foraging grounds of many waterbirds, including the clapper rail. However, the birds used it for nesting and cover from predators.

Beginning in 2005, the San Francisco Estuary Invasive Spartina Project began using helicopters, hovercraft and spray-packs to make coordinated herbicide attacks. Once the grass is eradicated, native vegetation recolonizes quickly. But much as A6's breaching spelled change for gulls and plovers, there were unintended consequences: Over the next five years, the already slim rail population declined by about 15 percent.

Cory Overton, another USGS wildlife biologist, has been slipping through the marsh since 2007, tracking these solitary birds. They're highly territorial, he says, so their population is tied "one-to-one" to available habitat. Each bird defends about five acres. (A major league baseball field is about three.) "You can't necessarily cram more birds into smaller areas," says Overton. "The best bang for your buck is new marsh."

Contrast that with semi-colonial plovers, where you might find a nest scrape or two every few acres. "Because plover ecology and behavior is so different, you can probably do more with less land," Overton suggests, especially if you keep out predators -- and keep humans at a distance, on trails. Potentially, you can also make new habitat, just like the retired salt ponds. "But you just can't make a tidal marsh where it hasn't been before," says Overton. "It has to be at the right elevation, with the right wave action. We can do a lot of things, but we haven't figured out how to control the tides."

We can, however, provide clappers with a temporary place to escape to during the highest tides, when they can be exposed and easily picked off. Between the Oakland Airport and the A's Stadium, in a tract called Arrowhead Marsh, Overton's group has anchored a fleet of "floating islands": platforms with small tents made of woven-palm fronds. Clapper cams have shown they're much appreciated.

Still, says Overton, "Everybody prefers a natural alternative to an artificial one." That means more genuine marsh. "The San Francisco Bay is one of the most invaded ecosystems on the planet," he observes. That's no exaggeration -- the estuary was described as North America's most invaded aquatic ecosystem in a 1995 report for the Fish and Wildlife Service, primarily because so many foreign bilges have come to port and released their ballast water. What's changed? "From mussels and clams and tube worms that live in the bottom, to the fish that are swimming through the sloughs, to the plants," says Overton. "You can't make the bay a pristine natural system," he admits. "But you can make it a functioning tidal marsh. That's still restoration."

The stuff of floating islands -- of ingenuity and determination -- might make the difference for plovers, too. Whatever amount of pond habitat remains will need to be enhanced. Across the Bay, for instance, is an experimental plot -- "the bird laboratory" -- in pond SF2, nested in the R complex beside the Dumbarton Bridge: 30 giant islands for nesting and high-tide refuge. SF2's archipelago was constructed for $9 million in 2010 as part of the restoration's first phase, and what happens there will inform future projects. "At low tide, a lot of mud flat is exposed," says Strong –– providing forage for shorebirds. "And there are deep areas for dabbling ducks." In 2011, 154 avocet nests and five snowy plover nests were counted on the islands -- a real success. Then again, if you concentrate waterbirds, predators might notice. SF2 is far from the gulls' home range, but for similar projects nearer Alviso, says Ackerman, "all that effort essentially could be devastated if California gulls go in and depredate."

In general, the restoration project is trying to do more with less, and that, too, could buoy the plover. "They have been here for almost a hundred years now," says Robinson-Nilsen, and with little human presence, "this is one pocket where we can do something pretty easily to help them survive." The bird observatory has tried to help the birds by enlisting volunteers to leave footprints -- plovers nest in incongruities -- and sprinkling white shells across dry pond bottoms for camouflage. But they're still searching for effective, low-budget ways to improve plover habitat.

Ultimately, significant acreage will need be to left for snowies if they're to hang on, says Robinson-Nilsen, and those ponds will need to be meticulously managed, drawing down water in late February, while ensuring ditches stay full all summer for wet pecking grounds. The restoration plans to provide nine dedicated plover ponds. SF2 includes one such "nursery," which incubated 13 nests in 2011. But this winter, pond E8a -- where 60 nests were found in 2011 -- was breached and flooded; though it could be a natural fluctuation, 81 fewer nest scrapes were found in the South Bay this year.

The restoration is designed to proceed cautiously, as part of its adaptive management philosophy. Its plan outlines "triggers" for individual species, red flags that would compel the project to pause, reassess -- or halt altogether, even short of 50/50. Snowy plovers would pull their trigger by dipping below the 99 birds counted in 2006 before restoration commenced, or by declining in number for several years. "But we can't guarantee species will use the habitat we create and enhance," says John Bourgeois, the project's executive manager. "Birds do unpredictable things." This year, no plovers were seen on SF2's pricey islands.

The official Bay Area recovery goal is 500 breeding plovers, and 3,000 for the entire coast. Robinson-Nilsen thinks anything more than 250 is a stretch, though, even under the 50/50 scenario. "Where are the other 250 going to go? There's almost no habitat anywhere else. Partially it's that this target did not take into account the restoration -- the fact that their habitat is going to be cut in half in the next 10 years."

We sat in the truck for another hour, keeping the rousted gulls off the levee between A22 and A23. There were just 23 gulls when we arrived this time, and the bird observatory was going to scale back hazing. "One day, they definitely kept me on my toes," Robinson-Nilsen remembered. "I was so glad that this area is closed to the public because I'm sure I looked crazy." Hundreds of the rascals circled and settled behind the Explorer, again and again. An interspecies game of chase ensued. Now, the wind rocked the truck, whistled around its mirrors. "Last night," Robinson-Nilsen told me, "I had a dream that we found two gull nests on this levee." The nightmare jolted her awake. "But that's not true yet. Hopefully, it won't be."

Her premonition hasn't transpired. Twelve thousand of A6's evicted gulls conveniently nested in the adjacent A14 colony last year, while others were absorbed safely elsewhere. And oddly, only 38,000 nested in total. For whatever reason, many apparently didn't attempt to breed.

This year, the breeding gull count is 52,700, a new record. But the gulls didn't even show up at the levee I helped defend. Instead, they tried to seize several of SF2's new islands, which, says Robinson-Nilsen, "is the last thing we wanted." So the bird observatory resumed its patrol by kayak -- a little bit more challenging, especially since Robinson-Nilsen is currently pregnant. Every day for three weeks, she paddled out, blowing her whistle sharply. The birds flew to a neighboring islet. She gave chase, no doubt looking crazy.

Movement, you might say, is the estuary's only surety. After all, the Bay didn't exist until about 10,000 years ago, when the ocean first slid through the Golden Gate after the last ice age. The marshes didn't settle until 3,000 years ago, when the sea level steadied. Before the salt ponds, there were no snowy plovers, fewer waterbirds; before the landfills, and perhaps the Mono land bridge, no California gulls to harass them. Only recently have we begun to influence these tides, let alone become aware we were doing so. Yet now we help decide which species go where, or even which survive.

On the levee last year, I asked Robinson-Nilsen if she ever felt a sense of loss about what was once here, before we filled it in and blocked it out. "It's amazing to think about this landscape before all this development," she replied. "Wetlands stretching as far as the eye could see. But still, there's so much wildlife here -- it's just different wildlife."

Nick Neely is a Bay Area native, or perhaps invasive. After receiving a master's in literature and environment from the University of Nevada, Reno, he interned at HCN in 2010, and now lives (temporarily) in New York City. He sends his sincere apologies to the salt marsh harvest mouse, for devoting all of his words to the birds.

This story was made possible with support from the Kenney Brothers Foundation.