Mountains and Marshes. David Rains Wallace
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to see them as winter versions of redstarts. The redstart’s winter home in Africa was unknown.
Two millennia later, the English essayist Robert Burton was as puzzled as the Greeks: “In winter not a bird is in Muskovy to be found,” he writes in his 1621 Anatomy of Melancholy,
but at the spring in an instant the woods and hedges are full of them, saith Herbastein. How comes it to pass? Do they sleep in winter like Gesner’s Alpine mice; or do they lie hid, as Olaus affirms, in the bottoms of lakes and rivers, holding their breath? . . . Or do they follow the sun, as Peter Martyr manifestly convicts out of his own knowledge; for when he was ambassador in Egypt, he saw swallows, Spanish kites, and many such European birds in December and January. . . . Or do they lie hid in caves, rocks and hollow trees, as most think, in deep tin mines or sea cliffs, as Mr. Carew gives out?
Burton retained something of the medieval tradition of relying more on scholarship than personal observation for information. But two centuries later, Gilbert White, a close observer whose The Natural History of Selborne initiated today’s nature writing tradition, remained unsure about many birds’ seasonal disappearances from the Hampshire countryside, which he had studied all his life. Geographic exploration had shown that birds departing in the fall went south and that others came from farther north at the same time. But White still found it hard to believe that little finches, thrushes, and flycatchers could fly all the way to Africa. He also could not confidently reject the traditional belief that swallows and swifts dived into lakes and ponds to spend the winter dormant in mud. Their behavior contributed to this idea, since they spend a lot of time swooping over water to catch insects.
Technology solved those problems. Researchers put radio transmitters on white-fronted geese in California, follow them to Yukon Delta breeding grounds, then to wintering grounds in northwestern Mexico. But the “why” and “how” of migration remain problematic. We know that billions of birds move out of the tropics every spring, seeking the vast food and space resources of northern summer. We know almost nothing about the phenomenon’s evolution.
Ornithologists once thought, for example, that showy songbirds like the orioles, tanagers, buntings, and warblers that nest here in summer evolved in North America and started migrating to the tropics when ice age cooling forced them south. But studies in the tropics found many resident species of our gaudiest summer migrants—orioles, tanagers, and buntings—and many are gaudier than ours. While some wood warbler species probably started migrating south because of global cooling, most of our summer songbirds probably moved north from the tropics as climate warmed. Two wood warbler species, the yellow-rumped and Townsend’s, winter here, but the orioles, tanagers, and buntings all go south.
Each avian group has evolved its migration patterns differently, and fragile-boned birds leave few fossils. There are, fortunately, still plenty of living ones to study. Yet the results are bewilderingly complex. Various birds seem to use every migration method imaginable short of compass and sextant. Almost all migrants probably steer by coastlines, mountain ranges, and other landmarks to some degree. Social birds such as geese and cranes have traditional routes that they teach their young. On the other hand, many fledgling birds make their first migration independently, implying a genetic programming that prompts them to fly in the right direction for the right distance. (Sometimes they fly in the wrong direction, which is why the Bay Area regularly gets a few eastern or Old World birds.)
Night-flying migrants, of which there are many, may steer by the stars; day-flying ones by the sun or, on cloudy days, by polarized sunlight. Pigeons and doves have tiny deposits of magnetic crystals in their heads that allow them to orient themselves by earth’s magnetic field. Some birds may hear low-frequency sounds like surf over long distances, which could help them follow coastlines or make landfalls when they are flying at twenty thousand feet at night, as many do.
Migratory birds have been a spectacular aspect of American history since Europeans arrived, if a sad one. Colonial naturalists, used to decimated Old World faunas, couldn’t believe the abundance and diversity of the birds they found in eastern forests and wetlands, but it took only a few centuries to make those qualities, in fact, unbelievable. It is hard now to imagine eastern forests with clouds of passenger pigeons and flocks of Carolina parakeets. Avian faunas were less spectacular as the frontier moved through the arid West, but when Europeans reached the Bay Area, they found huge migratory bird concentrations. Sir Francis Drake provisioned his ship for crossing the Pacific with seabirds and mammals from the Farallon Islands.
As elsewhere, colonists quickly reduced those concentrations. Market hunting became a ruthlessly efficient industry and remained so into the early twentieth century. By the 1820s, Russian fur traders were killing fifty thousand western gulls a year on Farallon breeding islands for meat and feathers. Even the fishy-tasting eggs of seabirds such as murres from the Farallones became a profitable commodity in the days before chicken farms. An estimated four hundred thousand common murres originally nested on the islands; by 1900, “egging” had reduced the population to about twenty thousand.
In the long run, however, conversion of habitat, particularly Bay marshes, into farmland, salt ponds, and towns had a greater overall impact. It’s hard to say what bird species habitat loss may have extirpated from the area, since little is known about what was here and the loss happened so fast. At least one disappearance is well-known, that of the yellow-billed cuckoo, a South American migrant that bred in Bay Area riparian woodlands into the nineteenth century. Civilization’s thirst for irrigation water had expunged it by the twentieth.
Considering San Francisco Bay’s importance as one of the world’s major estuarine harbors, the late-nineteenth-century’s conservation movement might have championed its bird habitats, but the Bay’s economic potential outweighed this. John Muir may have worried about ducks and shorebirds as he managed his fruit ranch in Martinez in the 1880s and ’90s, but there wasn’t much he could do about Bay wetlands, as opposed to remote Yosemite. (And the city even got part of that in Hetch Hetchy Reservoir.) In 1909, the United States designated some of the Farallon Islands as a national wildlife refuge, but aside from kicking out the market hunters, it did little to protect wildlife. Through the 1920s, as early federal refuges dotted more rural regions, the Bay Area maintained the boomer stance typical of the forty-niner past. Entrepreneurs had plans for the Bay itself—filling it for real estate—and its waterfowl habitat didn’t get even a nominal national refuge like the Farallones.
In the 1930s, a series of disastrous drought years coupled with the Depression focused attention on the need to protect some habitat for plunging bird populations and on opportunities to do so as land values also plunged. The federal government suddenly wanted more information about migrating birds—particularly the waterfowl that hunters value—and some kind of context for their overall management and protection. As it happened, little Lake Merritt—less posh by then after the mansion owners moved on but still offering winter refuge to waterfowl—played a big part in the enterprise.
An ornithologist named Frederick C. Lincoln had been running the U.S. Biological Survey since 1920. (The survey, a Department of Agriculture agency until its transfer to the Department of Interior in 1939, became the U.S. Fish and Wildlife Service, which runs today’s refuges.) While accumulating banding and recovery records from across the continent, Lincoln had noted the faithfulness with which ducks and geese returned to the places where they’d been banded. Among pintails and widgeons banded at Lake Merritt from 1926 into the mid-1930s, he found that nearly 97 percent of band recoveries were made west of the Rockies. In the winter of 1933–1934, more than half the ducks trapped on the lake bore bands attached there in previous years.
There was a good evolutionary reason for this. Before its conversion into urban scenery, the tidal inlet that is now Lake Merritt had been ringed by extensive seasonal wetlands. The ducks banded there must have had ancestors that frequented the area going back many thousands of years. It is encouraging, in a way, that their ancestral wetland’s conversion first to a sewer and then to a still-polluted ornamental lake didn’t deter them from returning, although, given the overall situation, where else could they go?
Lincoln coordinated this data with material from other sites showing that different migrants, like shorebirds and songbirds, also often returned to the same nesting and wintering locations. He used the