Nature Notes: The wings of March

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Sandhill cranes gathering in the evening during the 2008 spring migration. (Mark J. Harlow/markjharlow.com)

Photo by Mark J. Harlow

 

By Paul A. Johnsgard

For naturalists, March is a time for rejoicing, for on its soothing south winds sweep wave after wave of northbound migrant birds. By the first of March, the Platte River has usually fully thawed, although thin ice shelves might line its edges on frosty mornings, and dying snow patches are usually confined to deeper ditches and the shady sides of buildings.

Meadowlarks are appearing on fence posts along country roads and are tentatively starting to reclaim old territories or establish new ones. In towns and cities, cardinals have already been singing enthusiastically from trees and shrubs for nearly two months. Northbound sparrows and horned larks are now abandoning their winter foraging grounds in weedy edges, stubble and plowed fields, and are disappearing from view, only to be replaced by countless red-winged blackbirds, whose loose flocks dance over the fields like restless spirits, searching for brief resting places.

Early March is a time in Nebraska when the natural world changes on an almost day-to-day basis, with spring arriving in erratic fits and starts, as bone-chilling north and welcome south winds blow across the plains in regular

alternation. Nevertheless, day lengths during early March are increasing at a perceptible rate, and the sunrises and sunsets creep ever closer toward marking exact eastern and western compass points on the horizon.

As recently as 40 years ago, the first of March represented the average arrival date for sandhill cranes at the Platte River. Recent warmer winters and earlier thaws have tended to shift their first arrival date back into late or even mid-February, the birds being driven ever northward by a combination of hormones, experience, and melting ice. Thus, by the middle of February there are now usually a few flocks of cranes braving the possibility of late blizzards and icy Platte River waters, giving them early opportunities at the waste grain scattered across the harvested cornfields of the Platte Valley, from Grand Island west to Scottsbluff. Those stopping on the Platte’s eastern reaches are mostly headed for breeding areas in northeastern Canada, while the westernmost flocks staging along the North Platte River are headed to western Alaska and Siberia, as far as 3,000 miles distant.

The sandhill cranes arrive in the Platte Valley none too soon. By the time they arrive, vast flocks of cold-tolerant snow goose are already present, and thousands of overwintering Canada geese are harvesting corn from fields all along the central and western Platte Valley. Overwintering by Canada geese in the Platte Valley has greatly increased in recent decades, so that tens of thousands of birds now often sit out the winter there, rather than pushing farther south. The snow goose flocks that now number close to two million and that once migrated northward along the Missouri Valley have shifted westward to the Platte Valley during the past few decades, perhaps because of greater foraging opportunities there. Scattered among the snow geese, and comprising about two percent of the flocks, are nearly identical Ross’s geese, miniature versions of snow geese that are also headed toward high-arctic nesting grounds.

Add to these multitudes the tens of thousands of cackling geese and the probably larger numbers of greater white-fronted geese staging in the Platte, and the March goose population in the Platte Valley and adjoining Rainwater Basin to the south may easily approach three million birds. And, adding to the mix, mallards and northern pintails are the vanguards of a dozen or more species of ducks that pour into the Platte Valley and Rainwater Basin during early March. All in all, it is an avian spectacle possibly unmatched anywhere in North America, with perhaps 10 million waterfowl and half a million sandhill cranes concentrating in the Platte Valley at peak numbers.

And, if rarity rather than uncountable numbers is the naturalist’s goal, then the possibility also exists of seeing a few whooping cranes, one of North America’s rarest and most beautiful birds. Probably all of the historical Great Plains flock of whooping cranes, which now numbers nearly 300 birds, pass through Nebraska each spring, however, whooping cranes tend to arrive

later in spring than do the sandhill cranes, and very few are likely to appear before the first of April. They also migrate in small, family-sized groups, and, to avoid unnecessary (and illegal) disturbance and harassment, their exact stopping points are never publicized by state and federal agencies. As a result, it takes great luck to encounter any whooping cranes in the state.

Even rarer in Nebraska than whooping cranes are the ”common” cranes of Eurasia, which have been reported in North America less than a dozen times. Most of these sightings have occurred in the Platte Valley, where the birds have unexpectedly appeared among flocks of sandhill cranes. Probably these birds headed east, rather than turning south, on reaching the Bering Strait during fall migration out of Siberia, and followed sandhill cranes to their Great Plains wintering areas.

Unlike waterfowl and songbirds, which often migrate at night, cranes are daylight migrants, mainly because they rely on their soaring ability to carry them from point to point. By using thermal updrafts, which develop during warm days as sun-warmed air rises up from the ground, the birds can ascend thousands of feet with little physical effort, and then glide on a slight downward flight path for many miles, until they locate another thermal.

At a flight speed of 45 to 50 miles per hour, sandhill cranes can cover up to 500 miles in a single 10-hour day, or nearly all the way from their Texas and New Mexico wintering grounds to the Platte Valley. It is a great joy to be watching and waiting along the Platte after a warm March day and hear the clarion calls of arriving cranes thousands of feet above, as they recognize their long-remembered roosting sites of the Platte and begin a lazy circling glide downward to land among its protective sandbars and islands.

For the sandhill cranes, the Platte River offers safe nighttime roosting sites on sandy islands and bars sufficiently far from shore that coyotes or other land mammals can’t reach them without wading through water and alerting the birds to possible danger. During the daylight hours, from about sunrise until sunset, the birds spend their time in harvested cornfields and wet meadows, eating predominately corn, which is rapidly converted to fat stores needed for completing the long migration to arctic tundra. A small percentage of their Platte Valley food consists of various invertebrates, such as snails and earthworms, providing the protein and calcium that will be needed for egg-laying and other aspects of reproduction.

The middle of March is the peak of goose migration in the Platte Valley, with the goose population at or slightly past its peak, and the sandhill crane migration nearing its peak. This is the ideal time for venturing to the Platte Valley between Grand Island and Kearney, the focal point of goose and crane concentrations. There one might arrange to observe the dawn and dusk flights out of and back into the river roosts by the sandhill cranes in the

comfort of riverside blinds, such as those provided by Audubon’s Lydia Annette Rowe Sanctuary near Gibbon (308-468-5182). One might also watch from free public viewing platforms situated along the river at bridges south of Alda and Gibbon (off I-80 exits 305 and 285), or from the hike-bike bridge over the Platte at Fort Kearny State Recreation Area (off I-80 exit 272). Remember to bring binoculars, warm clothes and perhaps a camera!

During the day motorists may watch cranes and geese feeding in fields near the river (by driving country roads such as the Platte River Road from Donaphan west), and revel in the countless skeins of geese and ducks passing overhead, spread out from horizon to horizon, like animated strings of Christmas decorations. Avoid leaving the car and flushing the flocks during these times, as it not only needlessly disturbs the birds but also robs them of the precious foraging time they must have for replenishing their energy stores.

In recent years perhaps 20,000 to 40,000 people have annually made trips to the Platte Valley in March to witness this unique spectacle, and I have personally accompanied visitors from as far away as Europe, Pakistan and Japan. To do so is to provide a gift easily given, and one that I know they will carry in their memories and cherish for a lifetime. It is also a gift that all Nebraskans who love the natural world should consider giving themselves.

 

“Nature Notes,” provided by members of Wachiska Audubon Society, features writings by the society’s members on subjects related to nature and the seasons and relevant environmental issues. For more information, visit www.wachiskaaudubon.org.

 

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