Wednesday, November 23, 2011

Ring-billed Gulls -- © Dave Spier

Juvenile Ring-billed Gull at Lakeshore Park (on Seneca Lake) in Geneva, NY [November] © Dave Spier

Gulls are commemorated by a statue in Salt Lake City for saving the day when they ate the insects plaguing early Mormons in Utah.  Less dramatic are the local flocks of gulls that follow plowing tractors to feast on fleeing insects and (I suspect) mice and other small creatures like earthworms.  Gulls’ diets benefit in other ways from human activity.  To see this, just visit a landfill (unless they have trained falcons to patrol the skies).  The gull’s natural role in nature is being a scavenger cleaning the beaches of dead fish, but in reality these birds are omnivorous.

There are three gull species likely to be found in the Finger Lakes region and Lake Ontario during the winter.  Of these, the smallest and probably most numerous is the Ring-billed Gull (Larus delawarensis), sometimes nicknamed the “parking lot” gull.  It’s the one most adapted to life inland away from the sea.  It’s named for the black ring near the tip of the adult’s yellow bill.  Young ring-bills have a pink or flesh-colored bill with a black tip and we’ll discuss other differences.

Juvenile Ring-billed Gull at Lakeshore Park (on Seneca Lake) in Geneva, NY [November] © Dave Spier
Ring-bills require three years to reach maturity.  First-winter birds resemble very dirty adults with dark bars beside the chest, dark streaky heads, spotty sides, mottled brown areas on the wings and a black band across the end of the tail.  The legs are pinkish, unlike the adults yellow legs, but the backs are starting to turn gray.  Second-winter birds are much more adult-like overall.  In addition, legs become pale grayish-green or yellowish and the dark band at the end of the tail becomes broken and thinner.  By the third winter, the gray mantle extends across the back and upper wings -- except for the ever-present black wing tips.  The tail is now all white.  After the first winter, all non-breeding gulls show a little brown on the back of the head.  After adults molt to spring breeding plumage, this brown tinge disappears and a red orbital ring becomes more prominent around the pale eye.  Adults show a white spot at the end of sharply-contrasting black wingtips.

Adult Ring-billed Gull at Lakeshore Park (on Seneca Lake) in Geneva, NY [November]
© Dave Spier
The natural range of the Ring-billed Gull is transcontinental from the Canadian Maritimes to the Pacific Northwest.  Most of these birds travel to the southern states and coastal areas in winter, but the Lower Great Lakes and St. Lawrence Valley are mild enough with open water to hold a sizeable population throughout the year.  Ringbills seem to be born with a magnetic sensitivity that would take them in the right direction for fall migration.

Mixed-age Ring-billed Gulls at Sodus Point on Lake Ontario, NY [November] First-fall juveniles bottom center and lower left, 2nd-fall juvenile at right [based on The Sibley Guide to Birds]  - © Dave Spier
Ringbills prefer to nest on islands away from predators, and they will return to the same nest sites year after year if conditions permit.  This behavior is called site fidelity.  They nest in colonies limited only by the size of available habitat.  Given how common and widespread the species is now, it’s hard to imagine that they were once extirpated from parts of their range as a result of hunting for the millinery (hat) trade in the 1800’s.  Their breeding range is again expanding.

Many of these birds also return to the same wintering locations year after year.  If it worked once, it’s likely to work again in terms of finding food and shelter.

Occasionally a few Bonaparte’s Gulls will spend the winter along Lake Ontario.  This fourth species is smaller than the ringbill, has pink legs, a thin black bill and sports a dark “ear” spot behind the eye.  During spring and summer, adult Bonaparte’s have a black head.

As time permits, I’ll talk about the two larger common gulls.
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