August 2018

Vol. 46, No. 4

At a Glance: June 2018 Revealed

Wayne R. Petersen

Wayne Petersen

As a departure from the usual AAG photo challenge, in this issue readers are invited to identify four different individuals in a single image. At the expense of assuming too much, I suspect most readers will recognize that all four mystery species are gulls—a fact that may not thrill some, given that gulls are rightfully perceived as sometimes challenging to identify. To solve this identification puzzle, one of the first things to note among these gulls is that there are two large individuals and two smaller individuals.

Though there are different ways to attack a gull identification problem, one way is to assess the age of the gulls. Because the large gull on the far left has a solid light gray mantle, it is fair to assume that this individual is an adult. Immature gulls typically show some degree of two-toning, patterning, or mottling on the back and wings as the result of a contrast between feathers of different ages. This phenomenon is one reason why gulls often exhibit a high degree of variability from one individual to the next. The large gull on the left also has a pure yellow bill with an orange spot near the tip—another indication that it is an adult. In fact, it is an adult Herring Gull (Larus argentatus).

A close look at the smaller gull at the extreme right of the photograph shows a darker gray mantle than any of the others, extensive black on its folded wings, a black bill, dark legs, and a dusky mark behind the eye that runs around the back of the head. With these characteristics, the smaller gull on the extreme right is an adult Laughing Gull (Leucophaeus atricilla) in nonbreeding plumage.

Considering the plumage comments above, the two gulls in the center are clearly immatures (subadults). The immature bird on the right is about the same size as the adult Laughing Gull to its right, but is noticeably smaller than the immature bird to its left. Compared to the bird on its left, it also has a smaller and more rounded head, a much shorter, dark-tipped bill, and long and slender folded wings, all of which identify the bird as a young Ring-billed Gull (Larus delawarensis).

The final identification mystery is for the immature bird in the left center of the photograph. A close look at this bird shows a solid black bill, a whitish upper breast with light streaks that blend into a darker upper belly, a prominently masked appearance to its face, and noticeable white tips to the dark tertial feathers showing above the folded wing tips. The black bill and whitish chest that gives way to the lightly streaked appearance of the underparts when combined with the bird's long and slender folded wings all point to this gull being a young Lesser Black-backed Gull (Larus fuscus)—a species now regular in Massachusetts but often overlooked because of its close similarity to immature Herring Gulls.

Herring and Laughing gulls commonly nest in Massachusetts at various coastal locations, however Laughing Gulls migrate south in the winter. Ring-billed Gulls are common to locally abundant migrants and nonbreeding visitors practically throughout the year and throughout the state. Lesser Black-backed Gulls are scarce to uncommon visitors and migrants throughout Massachusetts but are most numerous on outer Cape Cod and Nantucket from late summer through the winter. The author photographed the mystery gulls in Manomet, Massachusetts, on October 7, 2007.

Wayne R. Petersen

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