Alcids and Evolution

Razorbills

Day before yesterday the Brookline Bird Club sponsored a tour around the Cape Ann coastline hoping to spot alcids, seabirds that normally winter offshore diving for food in nutrient-rich waters above the Continental Shelf. If you're lucky and persistent you may see individual alcids near shore. More often they're specks hurrying by half a mile out, glistening white bellies contrasting with rapidly beating black wings.

Razorbill

Razorbills are the commonest alcids that might be glimpsed at Halibut Point, mostly beyond crisp camera range. They have distinctive silhouettes, heads tilted back and upward like a loon, large bills dominating their foreheads.

Dovekie

Pigeon-sized Dovekies are the smallest of local alcids. Their short broadly conical bills are adapted to catching tiny crustaceans underwater. A Wikipedia article notes they may require 60,000 of these a day to support themselves in the North Atlantic. Like the other alcids, they only come to land during nesting season.

Dovekies were the advertised prize goal for the Brookline Club tour. For many in the group it would be a Life Bird, meaning their first authenticated sighting if they had a lucky day.

Black guillemot, fall-winter plumage

A more likely observation from shore is the Black guillemot, which may be seen here at this season either in its high-contrast breeding plumage or in the whitish eclipse plumage it takes on in late summer and fall.

Black guillemot, breeding plumage

Guillemots are more adapted to fishing near shore than the other highly pelagic alcids.

Thick-billed murre and Common eider

Strong-swimming murres that pursue fish show a very different bill structure than a duck that pulls its food from the ocean bottom. Alcids are restricted to cooler northern waters because pursuit diving becomes less efficient in warmer waters. The speed at which small fish can swim doubles as the temperature increases from 41 to 59 °F, with no corresponding increase in speed for the bird.

Common murre

In our area Common murres may be the least common of the alcids that may reasonably be seen here, excepting the even rarer Atlantic puffin.

In the region where alcids live, their principal seabird competition are cormorants (which are dive-powered by their strong feet). In areas where the two groups feed on the same prey, the alcids tend to feed further offshore.

You will have noticed similarities in appearance between alcids and penguins. This carries over to their strong swimming ability and the use of their wings to gain speed and agility underwater. Both groups stand with an upright posture on land because their legs are located relatively far to the rear for best diving propulsion.

Although not to the extent of penguins, alcids have largely sacrificed flight, and also mobility on land, in exchange for swimming ability; their wings are a compromise between the best possible design for diving and the bare minimum needed for flying. [Much of the foregoing is from Wikipedia.]

Examples of Convergent Evolution:

(1) Dovekie's resemblance to (2) Diving petrel

(3) Razorbill's resemblance to (4) Magellanic penguin

Chris Leahy, The Birdwatcher's Companion

It would be easy to suppose that alcids and penguins are linked by common ancestors. However genetic analyses have demonstrated that their similarities have developed from independent like responses to similar ecological circumstances. Very different ancestors evolved to specialize on the same feeding opportunities to produce look-alike species in a process known as adaptive convergence.

Local resident Chris Leahy presents authoritative and alluring information such as this in his encyclopedic Birdwatcher's Companion (2004).

For the book's cover illustration he has chosen a pair of nesting Tufted puffins, Pacific relative of the Atlantic Puffin alcid I have yet to see at Halibut Point. One of these nor'easters I may squint into the winds, sleet, and frigid temperatures that drive pelagic birds toward shore in hopes of that first sighting. So far I've excused myself for the sake of my camera. Chris says that "in flight off Halibut in winter plumage they are easily overlooked: small, dull (no big colorful bill sheath) flying fast close to the water." And probably half way to the horizon. Happy birding to you!