The Lake Where You Live

People often describe ducks as serene on the surface but under the water, paddling like mad.

Something similar, and more pronounced, is true of loons.

We see them placidly floating along, alone or with a mate, and then submerging with a minimum of ripples. But while below they are lethal predators, superbly adapted to pursue and catch the fish in which they mainly feed.

Daughter Sonya and I once observed how deftly and powerfully they swim when a submerged when a loon passed parallel to the L-extension of the pier on which we stood, so that we could look directly down on it.

The legs and the oversized webbed feet (not the wings) do the work. Loons can propel themselves with speed and turn on a dime, the better to capture fleeing and darting prey. Their bodies are exquisitely adapted for the purpose. That’s a good thing, because adult loons have to feed heavily (about two pounds of fish per day), not to mention capture food for their voracious chicks, which may eat 900 pounds of fish during a breeding season.

One adaptation is density. While most birds have hollow bones that lighten their bodies and make flight easier than it otherwise would be, many of loons’ bones are solid, enabling them to dive while using less energy. In addition, the loon skull is thicker and heavier than in birds and fowl of similar size. 

In his book “Loon Lessons,” biologist James D. Paruk says that loons weigh about the same eight to 11 pounds as a bald eagle, even though the eagle is 20 to 25 percent bigger. (The trade-off for density is the long “runway” loons need to get airborne.)

All this enables loons to dive deep — as far down as 200 feet. They can remain submerged for as long as five minutes, although dives of about one minute are much more typical. 

Loons are also ideally shaped for underwater maneuvering. The skull is streamlined to reduce water resistance (drag). For similar benefit they have narrow shoulders and a long, narrow sternum (breastbone). Meanwhile the lower leg joints enable extreme forward extension of the feet, allowing the webs to grab more water and boost forward propulsion.

Other bones, plus muscles and tendons, are also specially adapted to for diving and the pursuit of elusive fishes. To capture fish, loons have a long, straight, sturdy and sharp bill. They actually have an easier time catching fish that swim erratically, like perch and bluegills, as opposed to swimming fast in a straight line. 

Once prey has been trapped by the bill, it is held in place by sharp projections on the roof of the mouth and the tongue that point toward the rear, acting like the barb on a fish hook. 

Temperature regulation is important for loons because they live in water cooler — and in the early breeding season much cooler — than their body temperature. For that, they have “an inner layer of feathers that acts almost like a layer of clothing,” Paruk writes. “Because these feather ‘sweaters’ are zipped tightly, they are also highly waterproof.”

So when you see a loon gliding smoothly along, remember the caliber of predator that gentle-seeming bird truly is.

Ted Rulseh, a writer, author and advocate for lake protection, lives on Birch Lake in Oneida County. Visit him and his blog at https://thelakeguy.net.