Grebes and Loons, Part 2

Two species of loons frequent the winter waters off Halibut Point while they await the thawing of ice on the inland and northerly lakes where they breed, nest, and raise their families.

Common Loon, lower left, and Red-throated Loon, upper right

The winter plumage of these birds can be distinguished by subtle differences in the grey-white patterns on their necks. An easier field mark is the heavier build and straight conical bill of the Common Loon, compared to the more delicate outline and slim, upturned bill of the Red-throated Loon.

Common Loon

Loons trail their legs and feet behind them in flight, which separates them from all the other coastline waterfowl except grebes. They are larger than grebes and without wing patches.

Red-throated Loon

Their drooping neck and head silhouette tends to be more pronounced among Red-throated Loons.

Common Loon, beginning to take on breeding plumage

A good look reveals the more checkered pattern on the back of a Common Loon. When possible, loons swallow their prey before surfacing, which is more easily accomplished with a fish than a crab.

Juvenile Red-throated Loon

Red-throated Loons show a speckled rather than checkered pattern on their backs, giving a slimmer, greyer aspect than Common Loons especially when young.

Common Loon in breeding plumage

A few Common Loons get a late start in their spring departure, so we get a glimpse of their spectacular breeding plumage and eerie yodeling out on moonlit water. Unfortunately I've never seen a Red-throated Loon in its colorful phase.

Webbed feet

Unlike most birds whose bones are air-filled around a porous structure, loons have dense bones. This extra weight makes them float low in the water and helps them dive as deep as 250 feet to search for food, driven by those powerful legs placed to the rear that make them great swimmers but hopeless walkers.

These aspects make loons and grebes appear superficially similar, but the resemblance is considered a case of convergent evolution involving strong selective forces encountered by unrelated birds sharing the same lifestyle at different times and in different habitat. They are both foot-propelled but the loon's feet are webbed unlike the lobed toes of the grebe, among other anatomical differences.

Airborne

Another adaptation by these essentially fresh-water birds is their ability to change seasonally to a briny environment where they necessarily ingest large amounts of saltwater. They are able to excrete excess salt through glands near their eyes. 

Loons seem to push the limits of combining underwater success with the ability to fly. They need a long runway, literally, to reach liftoff, but once airborne they are strong flyers navigating gale headwinds above the waves, and covering hundreds of miles in a straight flight during migration at speeds up to 70 miles per hour.