Everything is a tradeoff. That’s why some birds look funny. Each species competes in a specific niche, and each has evolved special characteristics that enable it to survive in that niche. Some of these tradeoffs are extreme. Weird bills, long legs, goofy tails and unusual wings are a few of the deviations that give certain species a competitive advantage.
Consider penguins. They are among the world’s most efficient underwater swimmers, using their stubby wings for speed and maneuverability underwater. Flight-worthy wings would only slow them down, so they have sacrificed the ability to fly.
Members of the Alcidae family have made nearly the same tradeoff. These include puffins, black guillemots, razorbills and common murres. All have short, stubby wings, which they also use to swim underwater. Unlike penguins, they have retained the ability to fly — barely. They have to beat their wings fiercely to stay aloft. They resemble bumblebees as they buzz by. The short wings also inhibit their landing ability, which might aptly be described as a controlled crash.
An extinct member of this family — the great auk — did lose its flight ability, which contributed to its demise when hunters killed the last one in the 19th century.
Scientists have assessed the physical effects of these tradeoffs. By measuring respiration rates, they’ve documented that it takes a murre about 30 percent more energy than a penguin to swim and chase food underwater. With its stubby wings, it takes a great deal of energy for a murre to fly, too. On the other hand, murres can fly faster than penguins can swim, and there may be some advantage to how quickly murres can evade predators and return to feed their nestlings. Certainly, penguins in the Antarctic need to swim fast enough underwater to avoid being eaten by leopard seals.
You can witness wing specialization for yourself. Tour boats visit Maine’s five puffin colonies. I’ll be the spotter for one of those boats over the next four weekends, when the Isle au Haut Ferry departs Stonington Harbor and ventures out to Seal Island off the midcoast. Trips will run each Sunday, from July 19 to Aug. 9. We’ll get a chance to watch puffins and their cousins buzz by like bumblebees.
Loons have made a similar evolutionary tradeoff. They are exceptional swimmers and keep their wings pulled in tight to the body while underwater. Their feet are far back on the body for better underwater propulsion. This sacrifices the ability to walk. At best, they can scoot forward on their bellies far enough to get into a nest. It’s impossible for a loon to take off from land and difficult even from the water. Loons must taxi along the surface for a considerable distance before getting airborne.
The wings of raptors also illustrate evolutionary tradeoffs. The wingspan of a California condor stretches nearly 10 feet. The wingspan of an American kestrel is only 23 inches. Gigantic wings are great for effortless soaring, lousy for speed. When was the last time you saw a vulture rush? If your prey is already dead, speed is unnecessary. Effortless soaring from a comfortable height is perfectly suited to finding roadkill.
The Buteo family of hawks also is rather slow. The only time they need speed is when they dive on unsuspecting prey; when that happens, gravity is doing most of the work. Hence, the wings are relatively large on red-tailed, red-shouldered, broad-winged hawks.
Falcons chase down their prey in flight. Their wings are short, swept-back, and pointed, like a jet fighter. Peregrines, merlins and kestrels are fast in the open, but you’ll never see them chasing birds through the woods. That requires supreme maneuverability.
Accipiters specialize in woodland maneuverability. Sharp-shinned hawks, Cooper’s hawks and northern goshawks all have short, rounded wings and long tails that allow them to flash through the woods, swooping in through the branches so quickly that their prey has little time to react. These are the hawks most likely to snatch a bird off a backyard feeder.
Somehow, Mother Nature figures it all out. Long legs are an advantage for wading birds, but how long is too long? A heron with longer legs could venture into deeper water, but it likely would be unable to spot fish in the murky depths. A big pouch is a terrific fishing creel for a pelican, but how would it fly with a bigger one? When would a woodcock’s bill grow too long for timber doodling? OK. Now this column is just getting silly.
Bob Duchesne serves as vice president of Maine Audubon’s Penobscot Valley Chapter. He developed the Maine Birding Trail, with information at mainebirdingtrail.com. He can be reached at duchesne@midmaine.com.