Quiz #10: Answer

To refresh your memory, here again is the photo for Bird Quiz #10.

As I mentioned in the quiz, the photo was taken in Oregon in September. As you can tell, the bird is standing on sand, eating a piece of a large fish. It’s pretty safe to assume I was at the beach.

Anyone who has spent time at the beach (or any large-ish body of water) will immediately recognize the bird as a gull. (Note that “real birders” never call these birds seagulls… one, because many species are found inland, and two, while there are California Gulls and Kelp Gulls and Glaucous-winged Gulls and many other gulls, you won’t find any “seagulls” listed in your field guide.)

Adult gulls are hard enough to identify. Most adult gulls are basically white and some shade of light to dark gray (all-dark Heerman’s Gulls are a happy exception). You have to look at details such as their beak, eye color (try that from a distance!) or leg color (hard to do when they’re sitting on the water)—or all three—to tell them apart. Young gulls are pretty much a nightmare of look-alikes that change every year. I struggle a lot identifying young gulls.

A quick glance through your ID book will tell you this isn’t an adult. I made it hard.

So… let’s narrow things down a bit. What do we know? The bird is on the Oregon coast, and it has speckled dark brown feathers, pink legs, a dark eye, and a dark bill with a pink base. It’s hard to see relative size from a photograph, but it was a fairly large bird, bigger than the adult California Gulls sharing the beach. I should have included that in my initial description last week. You can stop here and try to ID the bird again if you wish.

Now, looking in my field guide… I’ve described a lot of gulls!

When I start comparing pictures, however, I only see three species that are this large, and this dark, that are normally found in Oregon. (I realize it could be a rarity, but if I do happen to encounter a rare juvenile gull, I’ll be out of luck. There’s little chance of me identifying it!)  I narrow down the options to a Herring Gull, Thayer’s Gull, or a Western Gull.

This is where it’s handy to own more than one field guild. While the Thayer’s Gull in the National Geographic guide is pretty dark, Sibley’s drawing is much lighter. So are the birds I see online. While I’m not absolutely positive, I’m going to eliminate Thayer’s Gull. Now I look at the Herring and Western gulls, and read the description of the 1st year birds. Three characteristics jump out at me.

First, when compared with one another, Herring Gulls have a more slender bill while Western Gulls have a stockier bill. Both bills are all black the first summer. However, as the first winter approaches, the Western Gull’s bill develops a “pale base” while the Herring Gull develops a “pink base.” What do you think? Is the bill on this gull stocky or slender? And is the base “pale” or “pink”?

Here’s a photo of another gull, taken on the same trip to Oregon. This one still has the all-black bill.

Second, Western Gulls are darker overall than Herring Gulls, with more of a contrast between the brown feathers and white edges. This bird is quite dark: Western Gull?

And finally, Western Gulls tend to have a more rounded head; Herring Gulls square off slightly in back, like a fly-catcher (or similar the difference between Greater and Lesser Scaups). Of course, wind, position, and the personality of the bird make this an iffy field mark. I think my bird has a rounded head, but it’s rather hard to tell for sure.

So, where does that leave us? I initially ID’d this as a Western Gull, mostly because there were a lot of adult Western Gulls on the beach. Then, looking at the bill again, I wondered if it was pink enough to be a Herring Gull. From photos on the Sibley website, I don’t think so. Finally, I labeled the photo “Western Gull.” But honestly? I don’t know for sure.

For those of us who love making lists with neat check marks, not knowing is pretty annoying. On the other hand, nature doesn’t fall into neat categories. In fact, gulls have a habit of hybridizing. Both my books mention that most gulls of the Washington coast are Glaucous-winged/Western mixes. It’s quite possible this bird is a cross between a Western and a Herring Gull. Or not. I suppose the surest way to find out would be to catch the bird and raise it in captivity until it molts into its final adult plumage, four years from now. “Yes, Mr. Wildlife Officer, you see I was just curious….”

Sometimes, the best we can do is write down “Larid sp.”

Leave a Reply

Fill in your details below or click an icon to log in:

WordPress.com Logo

You are commenting using your WordPress.com account. Log Out /  Change )

Twitter picture

You are commenting using your Twitter account. Log Out /  Change )

Facebook photo

You are commenting using your Facebook account. Log Out /  Change )

Connecting to %s