A VOLATILE MIX

Dunlins (Calidris alpina) are sandpipers that winter in large flocks at and near the Washington coast. Because they are common, they represent an important part of the diet of wintering bird-eating falcons (especially Peregrine Falcons and Merlins). When you find a large flock of Dunlins, there is every chance that one or more falcons will be nearby, and you may be gifted with one of nature’s more spectacular shows.

This is what happened to us near Edison in Skagit County on January 2, 2010. A large flock of Dunlins (around 4,000) was feeding and roosting in the flooded fields along the Bayview-Edison Road, not far from Skagit Bay, so we stopped to watch them.

Almost immediately the flock flushed, and a Merlin flashed through them. It didn’t get one, then disappeared, maybe because too many of its big cousins were in the area. In the hour and a half we spent at the spot, we saw three different Peregrines.

An adult male and an adult female stooped on the flock several times each, scattering the sandpipers like confetti. But it was confetti with a purpose, as the birds flushed and then became dense moving objects, oscillating back and forth over the landscape in alternating brown camouflage and white flash as they showed their upper- or undersides.

The speed at which the falcons went through the flock was breathtaking. The male seemed faster than the female, perhaps only an illusion because of his smaller size. After each pass, the predator would gain altitude quickly, then come back through in a dive. It would level out not far above the ground or water and come shooting through in level flight.

One would think any capture would be because of a random meeting in the air, but the falcon often jinked sideways or up or down slightly, presumably going after an individual bird each time. Their success rate was low; we never saw either bird catch a Dunlin, but a bit later we saw the female eating one, so she must have succeeded when we weren’t watching.

The biggest show was put on by a young female, easily distinguished because of her brown upperparts and striped underparts. She shot through the Dunlin flocks again and again, stooping perhaps 25 times as we watched. A lightning pass at eye level, sometimes coming within 50 feet of our car, then up and down again for another pass. She never picked one out of the air, but then we saw her circle around and pick one up from the water, presumably a casualty of her strike or a midair Dunlin collision.

We saw a Glaucous-winged Gull carrying a Dunlin in its bill, presumably another bird that hadn't survived the aerial confusion.

It was impossible to follow a stooping falcon with the camera lens, but by focusing into the middle of the Dunlins and hitting the shutter button just as the immature Peregrine passed, I managed to get a few photos during the attacks. The two adults obligingly posed for photos on nearby utility poles.

There was also a nearby Prairie Falcon that we never saw harass the Dunlins, perhaps because it already had something for lunch. A male Northern Harrier also passed through the waves of Dunlins but with no luck.

What a way to begin the New Year!

Dennis Paulson

SWANS IN THE FARMLAND

The Trumpeter Swan (Cygnus buccinator) formerly bred widely across the North American boreal forest, but by early in the 20^th century it hovered on the brink of extinction because of overhunting, Since then it has been rigorously protected and managed, and it has bounced back and continues to increase.

When I arrived in Washington, we made special trips up to the Bellingham area to see Trumpeters at one of a few lakes where small wintering populations persisted. With four decades of additional protection, now thousands of them can be found wintering all over western Washington. It’s nice to have as many pluses as we can to compensate for the many minuses we suffer in overall biodiversity!

But we also have another species of swan in Washington, the arctic-breeding Tundra Swan (Cygnus columbianus). That species has remained more common over the years just because it is much more wide-ranging, but its populations seem more or less stable now, not increasing like those of the Trumpeter.

Nowadays both of these swans can be seen in large numbers in winter in northwest Washington. Trumpeters tend to winter on wooded lakes, Tundras on salt water or larger, open lakes, but here in Skagit and Whatcom counties, they find most of their food in farmlands. Some of these farmlands are managed specifically for the swans and Snow Geese that furnish spectacular displays of white winter waterfowl.

The two swans tend to forage in single-species flocks, but they also mix from time to time, usually a few of one species associated with a larger flock of the other. How do we tell them apart?

Tundra Swans are only about two-thirds the size of Trumpeters, as measured by weight, but they have to be seen in close proximity to be compared in this way. Their linear measurements are not so different, and all swans look big!

Most Tundra Swans have a small yellow spot between eye and bill, lacking in Trumpeter, but some Tundras lack that spot and look much like Trumpeters. The best way to distinguish these birds is by looking at the base of the bill adjacent to the eye. That area is broad in Trumpeter, so the eye looks like part of the bill, while it is usually distinctly constricted before the eye in Tundra, making the eye stand out.

This different configuration of the bill can present a different appearance at a distance, even in flight.

Being larger, Trumpeters may mature at a slightly later age, and they change more slowly from the gray immature to the white adult. In their first winter, Tundra Swans molt in many white or whitish feathers, so by midwinter the immatures are quite whitish. Trumpeters don’t do this, so by midwinter they are still leaden gray. Thus looking at the immatures is a good way to identify the species present in a flock. Even the whitest immatures are easily distinguished from adults by their dusky head.

Finally, the swan species have very different voices. That of the Trumpeter is a low-pitched sound that could be compared with an off-key trumpet. That of the Tundra is a higher-pitched honking, somewhat more musical than that of the Trumpeter, that might be likened to a flock of geese.

Dennis Paulson