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Bay Nature magazineOctober-December 2015

A Festival of Cranes

by Joe Eaton on November 03, 2015


In the early morning, greater sandhill cranes at the Cosumnes River Preserve prance, bow, call out, and touch beaks in an elaborate dance that often develops over years between mated pairs. (Photo by Lon Yarbrough, ShareTheRoad Productions).

F

rom high overhead comes the rattling cry that conservationist Aldo Leopold called “the trumpet in the orchestra of evolution.” Riding the autumn winds, the sandhill cranes are returning to the California Delta. Every year they converge here, part of a living wave that also includes swans, geese, and ducks arriving from the north to spend the winter. Among the vineyards, orchards, housing tracts, and dairy farms, the cranes in their thousands gravitate to a handful of roosting areas: Cosumnes River Preserve, Woodbridge Ecological Reserve, Staten Island, and other sites on private land. Their arrival is one of California’s supreme wildlife spectacles, a major draw for Delta visitors—and, like the migration of the monarch butterflies, a phenomenon we risk losing.

Sandhill cranes of three subspecies—the lesser (Grus canadensis canadensis), greater (G. c. tabida), and Canadian (G. c. rowani)—spend the winter in the Delta and the Central Valley. Lesser sandhills are to greater sandhills as grizzly bears are to Alaskan brown bears. They have followed separate evolutionary paths since Pleistocene glaciers divided their ancestral populations 1.5 million years ago, with some interbreeding since: Greater-lesser mating pairs continue to be, on occasion, observed in the field. As for Canadians, they weren’t recognized as a separate entity until 1965, and some ornithologists don’t accept them as a separate group given their similarity to the greater. Even experts have trouble distinguishing them in the field.

The cranes differ in size (as the names suggest), migratory behavior, food and habitat preferences, and protected status: In California, greaters are listed as endangered; lessers, a species of special concern; Canadians have no legal protection beyond the federal Migratory Bird Treaty Act. Greaters are more abundant north of the Delta, lessers to the south, while Canadian sandhills are far outnumbered by both subspecies in the Delta. Although they didn’t differentiate among subspecies, observers in the 1850s mentioned abundant wintering cranes in California’s grasslands. Market hunting thinned their ranks, but they slowly recovered during the 20th century, with their winter presence in the Delta increasing over the past 50 years. An estimated 50,000 cranes, four-fifths of them lesser, now winter statewide. The Delta, offering isolated shallow wetlands for night roosts and grain fields for foraging, may have compensated for lost habitat elsewhere. In a 2007-08 survey, Delta counts ranged from 6,421 in November to 27,213 in February.

cranes

A pair of greater sandhill cranes leaves their roost at the Woodbridge Ecological Reserve in the morning to forage in the fields. (Photo by Lon Yarbrough, ShareTheRoad Productions)

Distinguishing a greater from a lesser sandhill lies in the details. In a mixed group, the size difference is obvious, greaters standing almost a foot taller. In flight, lessers appear relatively long-winged, equipped for an epic trek from the far north: They migrate 2,400 miles from the Alaskan tundra. Greaters breed closer by, from British Columbia to Northern California as far south as Sierra Valley, with their highest concentration in Oregon.

Lessers and greaters behave differently in the Delta. Greaters arrive earlier in the fall and leave later in the winter, some lingering into March. Lessers forage in alfalfa; greaters avoid it. “Lessers move around the landscape more, focusing on maintaining their flight muscles by eating protein,” says Gary Ivey of the International Crane Foundation, who has studied cranes in California for years. They consume the larvae of orange sulphur butterflies in those alfalfa fields, earthworms, beetle grubs, crayfish, voles. The diet of greaters has a higher vegetable content, mainly waste grain, and they don’t travel as far from the roost to feed.

On the other hand, many behaviors are common to all sandhills. Their body language is eloquent. Waves of dancing propagate through winter flocks, and some birds may practice their crowd-drawing courtship moves (although the majority of courtship takes place in spring farther north). The extent of a patch of bare red skin on a crane’s head signals its emotional state. A relaxed bird shows only a small area of red, but excitement or anxiety increases blood flow and activates muscles that expand the patch to cover most of the top of the head. These intensely social birds have strong family ties. Pairs may stay together for life, but some break up after nest failures. Parents tend their offspring, oddly called “colts,” for nine or ten months after hatching and lead them south on their first migration. With luck, they’ll make many other journeys: Wild sandhills have survived into their third decade, with 40 the longevity record.

On the first full weekend of November, the Central Valley city of Lodi honors these winter visitors with a Sandhill Crane Festival. For almost 20 years its dual aim has been to attract tourists and promote awareness of the birds. Some festival-organized tours visit crane-viewing locations not normally accessible to the public, and tour leaders stress viewing etiquette: Don’t walk out into the fields toward the birds; keep your voice down. Cars make good blinds for crane-watching. “They hate motorcycles and bicycles,” Ivey observes.

Not far from Lodi, Staten Island provides a fine buffet for wintering cranes. Owned by The Nature Conservancy and managed by its affiliate Conservation Farms and Ranches, Staten is a wildlife-friendly working farm, growing corn, triticale, and other crops the birds favor. Laura Shaskey, conservation program manager at Staten Island, says up to 8,000 cranes foraged on the island last fall, and a record high of 11,700 used night roosts there. Of particular conservation importance, Staten hosts one of the densest winter populations of the state-endangered greater sandhill.

In its present iteration, the proposed Delta Twin Tunnels water diversion project would run directly through Staten Island. That route, announced in 2013, drew fire from environmental groups and other stakeholders; construction plans were modified last year. Ivey, who works with an advisory group, notes that the original version would have used the island for storage of dredged materials, affecting almost a quarter of the 9,200-acre tract. “We appreciate that overall impacts on Staten Island from the original proposed project have been substantially reduced both during construction and with regard to project operations over time,” says Jay Ziegler, TNC’s director of external affairs. “However, it is imperative that we protect habitat for sandhill cranes at Staten Island and create additional habitat [for them] in the Delta.”

Changing land-use patterns in the Delta have made places like Staten Island all the more crucial to the survival of Pacific Flyway sandhills. As far back as 2000, Ivey and veteran crane researcher Carroll Littlefield called conversion of grain fields to vineyards and orchards “the most serious factor threatening sandhill cranes wintering in California.” The trend has accelerated, with vineyard acreage in San Joaquin County alone more than doubling in the last 25 years. “How much can you lose within the core area before affecting the capacity of the landscape to hold the population of cranes?” he asks. Farther north, around Galt and Elk Grove, urban sprawl is a significant threat.

Literary celebrations of the sandhill crane stress the species’ antiquity. “His tribe … stems out of the remote Eocene,” wrote Leopold. In The Birds of Heaven, an account of his travels in search of cranes, the late Peter Matthiessen mentions the discovery of a nine-million-year-old leg bone of “today’s sandhill crane,” which seems to refer to a fossil found in Nebraska. But “it’s a leap of extreme faith” to assume the bone belongs to a sandhill, writes R. George Corner of the University of Nebraska State Museum, which houses the fossil.

To crane-watchers, though, the truth in the ancient bones may be less important than the feeling summoned by the bugling of the great birds. Eocene, Miocene, or Pleistocene, it seems primordial enough. “I can tell that people love hearing that sound,” says naturalist David Wimpfheimer, who has led many Delta crane tours. “It’s evocative of wild places. It transports listeners from plowed-over corn stubble to Alaska or the Canadian Arctic.” If the sandhill’s trumpet is ever silenced, our loss will be immeasurable.

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