Migrating tundra swans stop over in Delaware

• The snowy white tundra swan breeds in the Arctic and migrates many miles to winter on North America's Atlantic and Pacific coastlines%2C bays%2C and lakes. The eastern population frequents the Chesapeake Bay and North Carolina%2C while the western population typically winters in California.
• Average life span%3A Up to 20 years in the wild
• Diet%3A Omnivore. These large birds feed by dipping their heads underwater to pluck aquatic plants%2C tubers%2C and roots. They also eat shellfish and are developing an increasing taste for grains and corn found in farmland areas.
• Size%3A Body%2C 3.9 to 4.8 feet%3B wingspan%2C 5.5 feet%2C weight%2C 8.4 to 23.1 pounds

In a field west of Milton, a bird watcher was the first to notice the large flock of big, white birds feeding amid the cut over corn stalks.

One hundred tundra swans, white like a snow goose but much larger and with a longer neck and black bill, spotted on Thursday grew to a flock of 500 by the weekend.

For this time of year, it was unusual. Flocks like these are much more common in Southeastern Pennsylvania or the Eastern Shore of Chesapeake Bay.

"I suspect, as with many other waterfowl, the swans are just being opportunistic in feeding and staging depending upon the snow/freeze/food availability," said Bill Stewart, the American Birding Association director of conservation and Community and Young Birder programs coordinator. "They might just be getting funneled into that corridor due to the conditions."

Delaware gets tundra swans but typically hunters and birders see a few birds or a small flock as they migrate south for the winter.

Over this season, state officials received reports of tundra swans in the late fall and early winter but when it came time for the winter survey of migrating waterfowl in January, they saw half as many, counting about 500 total birds in the annual aerial surveys done in early January, said Matt DiBona, the state wildlife biologist who monitors migratory waterfowl and upland game birds.

Tundra swans are an interesting bird species because of a shift in their primary wintering range and their feeding strategy since the 1970s.

What biologists have discovered is that the number of wintering tundra swans along Maryland's Chesapeake Bay has declined while the number of birds wintering in northeastern North Carolina has increased.

National Audubon Society Christmas Bird Count data mirrors that finding. During a single day count in the St. Michaels, Maryland, area in 1972, the bird count team tallied 7,500 tundra swans. In 2013, they counted 196.

The birds were never that plentiful in Delaware's Christmas Bird Counts. At Bombay Hook National Wildlife Refuge, the team counted 12 tundra swans in 1972 and 79 in 2013.

As the Chesapeake wintering numbers declined, the North Carolina counts increased. Between 2002 and 2006 better that 65 percent of the east coast population of tundra swans were spending the winter in North Carolina. These days, some 65,000 to 75,000 birds spend the winter there. The remaining 25,000 are spread between Virginia, Maryland, Delaware, Pennsylvania and New Jersey.

There has been a similar winter swap in reverse with snow geese, DiBona said. They used to winter in large numbers in North Carolina but in the last few decades have stopped short in their winter migration in Delaware, Maryland and Pennsylania.

The shift in wintering grounds seemed to have tipped following the winter of 1969-1970. Delawareans might remember a dramatic, white Christmas in 1969, followed by a bitter cold January. Temperatures that month were 8.0 degrees lower than average.

Biologists found that tundra swans used to depend on wetland habitats rich with submerged aquatic vegetation, habitats that were common along Chesapeake Bay and its tributaries. But during the winter of 1969-70, the bay, rivers and creeks were frozen and the birds couldn't feed on the underwater grasses. They discovered the leftover corn and soybeans in area farm fields.

These days, it is common to see the birds feeding on winter wheat, barley and in cut-over corn and soybean fields. About that time, the winter population started to shift further south.

The spring migration hasn't changed. Normally as the birds migrate north, they travel through the Chesapeake Bay and into Pennsylvania where they feed in fields in the Lancaster area.

Ian Gregg, the Pennsylvania Game Commission game bird scientist, said much of that area is still snow-covered.

"We're just now starting to melt snow and ice," he said. So the birds might be looking elsewhere, such as Delaware, for food.

Tracking studies of the birds done in the early part of this century, found that tundra swans typically move north from North Carolina in March. Satellite-tagged birds often passed through Maryland's eastern shore stopping to feed for a few days. Then the birds flew non-stop to Lake Ontario. From there, they moved west across the Great Lakes and into Minnesota or the Dakotas before heading north to the high Arctic in Canada or Alaska. They arrive there in early June, breed and begin their southern migration in September.

Chris Dwyer, a migratory game bird biologist at the U.S. Fish & Wildlife Service regional field office, said he used to work in Ohio and can remember seeing hundreds of the birds feeding in fields as they staged to fly west and north in the northern migration.

Dwyer said that while the submerged aquatic grasses in the Chesapeake aren't common, officials in Maryland have been working to restore them.

Meanwhile, Gregg said, based on their satellite data, they found the same bird can spend one winter in Pennsylvania and the next in North Carolina.

"They do move around," he said.

Reach Molly Murray at 463-3334 or mmurray@delawareonline.com. Follow her on Twitter @MollyMurraytnj.