the underwater hunter

Quite by accident, while I was out in the Grass Lake marshes looking for the ospreys that should have been near their platform nest (the one usurped by a Canada Goose), a lone Common Loon popped up right in front of me.

Common Loon-

The morning had the perfect kind of filtered sunlight to bring out all the “color” in this black and white bird. For example, I’ve never noticed before how just the right angle of light turns the usually dark feathers below its white necklace into a turquoise band.  The loon’s head feathers are actually faintly iridescent.

During the breeding season, both male and female loons have brilliant red eyes, which might well be an indicator of their readiness to mate.  But loons are fiercely territorial and protective of their chicks, driving off other loons or intruders (like Canada Geese) far larger than they are, and it has been suggested that their red eyes are a threat advertisement of their presence.

Common Loon-viewing fish underwater

The loon frequently dipped its head below the water while paddling around.  It looks like a snorkeler checking out underwater life.

Common Loon-

Several times, following a bit of snorkeling, the loon would quickly dive below the surface, never making a sound or a splash.  I never saw it bring up a fish to swallow, but loons often swallow their smaller prey while underwater.

The Common Loon, or Great Northern Diver, as it is known throughout its range in Eurasia, has some unusual anatomical adaptations for its underwater life:

  • solid, instead of the hollow bones that characterize most birds, decrease the bird’s buoyancy in water and allow it to sink quickly during a dive
  • legs are placed so far to the rear of its body, loons can’t stand up on land, but must push themselves forward on their belly
  • rather short wings decrease drag as the bird propels itself through the water, but the trade-off is that reduced lift provided by the wings requires a long space for taking off into the air

But how does a bird that depends on its eyes for hunting underwater see both in air and in water?  Some have suggested that the birds’ third eyelid (nictatating membrane) which usually has a protective function, is more transparent in loons and other diving birds, and acts like a pair of goggles to preserve an air space between the pupil and the water.  Check out the video below for a good illustration of the underwater swimming activity of these unusual birds.

Common Loon-