Saturday, December 17, 2011

The Largest Gull

Adult Great Black-backed Gull (December) -- © Dave Spier

The Largest Gull
© Dave Spier

The world’s largest gull, the Great Black-backed (Larus marinus), is a coastal species of the Northeast.  It breeds in the Canadian Maritimes, migrates through New England and now winters from the lower Great Lakes to the mid-Atlantic coast.  When I started birding in the early 70’s, it was still an uncommon visitor to the Lake Ontario shoreline, but its range has expanded southward from the original North Atlantic stronghold.

As the name implies, the gull’s wings and back are sooty-colored (more like slate than pure black).  The underparts are pure white, but in the winter, the white head exhibits some dusky streaking.  The legs are light pink and the adult’s bill is yellow with a red spot toward the tip of the lower mandible.  Sailors nicknamed these birds “the coffin carriers.”

Immature Great Black-backed Gull (January) -- © Dave Spier

It takes four years for Great Black-back’s to reach adulthood.  Young birds have light-colored heads that are more of a pale brown.  Their bills are dark and massive.  Wings and backs are relatively dark with a fine checker-boarded pattern.  The feet may be pink, but the legs start out as a dark bluish-gray.  A light rump accents a dark tail band.  Over the next several years, they gradually morph into the high-contrast adult plumage.

Adult Great Black-backed Gull eating a fish; note passing Wood Duck (October) -- © Dave Spier

Gulls, by their nature, are scavengers.  Their natural diet is dead fish and their job in life is to keep the beaches and shorelines clean.  Most gulls stick to this formula, but the GBBG, by virtue of its size, has discovered that it can become a predator.  I discovered this aspect many years ago when I was driving down the east side of Seneca Lake and noticed a Black-back attacking a small duck.  The victim was a female goldeneye that kept diving to escape, but every time it re-surfaced the gull would peck away at the bloodied duck.  As I recall, the goldeneye finally got away, or else the gull just gave up the struggle and went elsewhere for easier pickin’s.  In the “modern” world, easier often means garbage.  Depending on the season, they also eat fish, invertebrates (including insects), small mammals, eggs and carrion.  Given the opportunity, they will steal food from other gulls.

Adult Great Black-backed Gull eating a fish on the Erie Canal (February) -- © Dave Spier

In the late 1800’s, before protection was enacted, Black-backs were hunted to collect their feathers to supply the women’s hat industry.  The result was a population crash.  In the long run, their numbers have rebounded and continue to rise as their range expands southward.  This has become a new problem along the Atlantic coast where the gulls prey on colonies of terns and puffins.

Adult Great Black-backed Gull at Montezuma N.W.R. (October) -- © Dave Spier

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