November 10, 2013

Birding: Herring gulls stand test of time

Nearly wiped out, they may be more numerous than ever.

By Herb Wilson

The herring gull is the most common and the most familiar gull in Maine. It is typically associated with the shorelines of the ocean, lakes and large rivers. These birds have readily adapted to human-altered landscapes so small flocks may hang out in parking lots, cadging french fries or other morsels from fast-food customers. Hundreds and even thousands of these gulls may be seen at open landfills.

In North America, herring gulls breed across most of Canada and in the northern tier of states from Minnesota to Maine. Many of those breeding herring gulls will migrate south for the winter, either along the Pacific Coast from southeastern Alaska to Baja Mexico or to southern states from Texas east to North Carolina. Some even migrate to Caribbean islands. Some herring gulls breeding along the coast from Massachusetts to North Carolina are year-round residents.

Although we think of herring gulls as abundant members of our avifauna, this species was nearly extirpated from North America in the 19th century by plumage hunters and egg collectors. Thanks to protection afforded by laws, populations in New England have been reasonably stable since 1970. Some ornithologists believe that herring gulls may be more abundant now than before the egg and plumage collectors began to take a major toll on the populations.

Adult herring gulls are fairly easy to identify. Look for the pink legs to start with. The head, neck and undersides are white, often speckled with black in the winter. The upper wings and the upper back (the mantle) are light gray. The wing tips are black with white spots (called mirrors). The eye is yellow. The massive bill is yellow to light orange with a red spot near the tip on either side.

Herring gulls require four years to attain sexual maturity and therefore their adult plumage. The immature plumages of herring gulls are a bit trickier to master and separate from other large gulls, but a little effort can be quite rewarding. The timing of the molts varies greatly among individuals of the same age and an incomplete molt leading from winter (basic) to summer (alternate) plumage adds to the challenge of aging a herring gull.

Take a look at your favorite field guide and you will see that the plumage of herring gulls gets lighter as they age. First-year gulls are mostly brown; their bills are dark. Second-year gulls are usually a bit lighter than first-years, particularly showing some white on the head and some gray feathers on the mantle. Their bills are black at the tip but are yellow at the base. Third-year birds still show some brown streaking on the head. Such a bird appears to be wearing a gray backpack, contrasting with the browner feathers on the outer part of the wing. The bill shows a bit of black at the tip.

The third-year plumage is the least frequently encountered plumage. Can you figure out why? To answer the question, let’s follow four cohorts of gulls over four consecutive years. Let’s say that 100 herring gulls are hatched each year and that 10 percent of them will die within 12 months. After those four years, we will then have 100 first-year gulls, 90 second-year gulls, 80 third-year gulls and 70 fourth-year gulls. But those fourth-year gulls are now in the adult or definitive plumage and will join the multiple-year class of adult birds. Herring gulls typically live to be 15-20 years old, with some exceeding 30 years old. With this piling up of birds of many ages wearing the same clothes, it’s not surprising that the adult plumage is the most commonly encountered, followed by first-year birds, then second-year birds and finally the third-year birds.

Herb Wilson teaches ornithology and other biology courses at Colby College. He welcomes reader comments and questions at:

whwilson@colby.edu

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