Some would say “a gull is a gull” and wouldn’t give it a second thought.

But last week a seasoned birder took a second look at some gulls in the parking lot of a grocery store in Thomaston and discovered one of them was something different.

In this case “something different” meant a mew gull, a species only recorded from Maine perhaps three times before this.

Mew gulls come in two general versions. One, which is now usually called “mew gull,” has a breeding range that extends largely across Alaska to British Columbia, Yukon, and the Northwest Territories with wintering birds making it south to California and northern Mexico.

The other version, usually called “common gull” and may be rightly considered a full and separate species from the North American “mew gull,” breeds in northern Europe and Asia (there are two other subspecies that breed in Russia but that’s more than you probably want to know).

Last we heard, it has not yet been determined whether the mew gull seen in Thomaston last week came from Europe or western North America, but either way it’s an exciting rarity to find here in Maine.

Our point in telling you about this sighting was not to get you to look for more mew gulls necessarily, but to consider giving a second look to all the birds you see, especially the common ones that you may take for granted.

Doreen and Jim Dun at Ocean Point kept their eyes open last winter and discovered a painted bunting at their feeder; a bird that should have been in Cuba or Mexico at that time of year.

Some area lobsterman took a second look a few years ago when cruising by Damariscove Island in the winter and made the very odd discovery of some white pelicans hanging out there for some strange reason known only to the birds.

A birder on a whale watching trip out of Bar Harbor in August 2010 took a closer, second look at what some might have just called a rather common sooty shearwater and discovered and photographed a white-chinned petrel, a species that normally stays in the Southern hemispher.

Observers taking a close look at the hummingbirds at their feeders or flowers in Maine have found such out-of-place species as calliope hummingbird, rufous hummingbird, and even the tropical-dwelling green violetear.

Even if you don’t find a rarity like this, and odds are that you won’t, you may find yourself marveling at some aspect of a common bird’s plumage or behavior that you had never noticed. Check out the multi-year stages of gulls that take them from brownish-speckled juveniles to, eventually, clean-looking gray or black backed adults (it takes four years in the large gull species).

In fact, this time of year is a great time for seeing the variability in the plumage of most birds, with lots of immatures floating around along with adults in worn plumage or molting into their winter garb. Yes, “winter garb!”

Summers in Maine are short for us humans, but even more so for some bird species, which means all the more reason to take “second look.”

Dr. Jeff Wells is the senior scientist for the Boreal Songbird Initiative. During his time at the famed Cornell Lab of Ornithology and as the Audubon Society's national bird conservation director, Dr. Wells earned a reputation as one of the nation's leading bird experts and conservation biologists. Jeff's grandfather, the late John Chase, was a columnist for the Boothbay Register for many years. Allison Childs Wells, also formerly of the Cornell Lab of Ornithology, is a widely published natural history writer and a senior director at the Natural Resources Council of Maine. Together, they have been writing and teaching people about birds for decades. The Maine natives are authors of the highly acclaimed book, “Maine's Favorite Birds.”