Monday, November 29, 2010

American Dipper... North America's only aquatic songbird

American DipperAmerican Dipper at Hagg Lake, Washington Co., Oregon on 24 November 2010 by Greg Gillson.


Some birds are very difficult to photograph. At least, I've had some trouble. One of those is the American Dipper. These gray aquatic songbirds live along rushing streams with steep banks edged by dense forest. So they are often in shade, with bright reflections off the water. The shade requires a slower shutter speed. Any shafts of sunlight are over-exposed. Slow shutter speed also means the bird must be still. And dippers got their name for their constant dipping, bouncing 40-60 times per minute on their legs even when standing in place.

On November 22 we got our first snow of the season. It wasn't much, as typical for western Oregon, just a bit as rain showers all week were pushed south by a cold front and the dry air behind it. By November 24 the roads had dried, the icy roads had mostly cleared. I went up to Hagg Lake at the edge of Oregon's Coast Range about 30 miles west of Portland.

At the upper end of the lake I stopped briefly to see if the resident pair of American Dippers were present at the Scoggins Creek Picnic Area, where this creek enters the reservoir. The birds were there, swimming and diving in the water, so I got my camera out. The leaves of the maples and alders were gone, and the quarter-inch of snow brightened up the creek under the western red-cedar and Douglas-fir. So I sat on a rock at the edge of the creek about 20 feet from the ledge where two birds were diving for caddisfly larvae--their favorite food.

Then something wonderful happened. The bird pictured here began his long, warbling, high-pitched song. It wasn't as loud as it will be in a couple of months, but clearly heard above the roar of the creek. It is not unusual to hear dippers singing throughout the year. But the bright cascading trills and sweet notes brightened the cold overcast winter day, when most other birds were silent.

Another thing that can ruin a good photo of a bird is the inner eyelid, the nictitating membrane. In some birds it is transparent, but is opaque in the American Dipper, as seen in the photo below, creating a vacant-eyed "Little Orphan Annie" appearance.


American DipperThe nictitating membrane, or inner eyelid, covers the eye of this singing American Dipper at Hagg Lake, Washington Co., Oregon on 24 November 2010 by Greg Gillson.


The nictitating membrane is under the eyelids. It sweeps across the eye from its base on the bill side of the eye. It allows light to enter. On birds with clear nictitating membranes they can see through it. It is thought many birds fly with their nictitating membrane closed--to keep the air from drying out the cornea. The well-developed nictitating membrane protects the eye of the American Dipper from the spray of water (The Audubon Encyclopedia of North American Birds, 1980 by John K. Terres).

A year ago I discussed How to find a Dipper nest. There is more information on these fascinating birds there.