Bird Quiz: Answer

To refresh your memory, here is the photo from October’s Bird Quiz. The bird was seen in Colorado at the end of August. Don’t read any further if you want one last chance to identify this bird.

10_JacksonLakeSP-CO_LAH_2198

To refresh your memory, here is the photo from October’s Bird Quiz. The bird was seen in Colorado during the month of October. Don’t read any further if you want one last chance to identify this bird.

Most people recognize gulls. They may not know that the “little pointy gulls” are actually terns, but they can at least find the appropriate section in a field guide. I’m going to assume you recognize this bird as being in the gull family and start there. And yes, You’ll not that it’s small and pointy, and rather compressed, as if something heavy sat on it sometime while it was growing up. Also, the beak is thin, long, and sharp. That’s how we know it’s a tern.

That was the easy part. Most terns are basically white and gray birds with black accents, and this one is no different, so we can immediately eliminate those with different colors.

At different times in the year, the patch of dark feathers on the head creeps backward to resemble a receding hairline, and not all “hairlines” are the same size and shape, or exactly in the same position. That’s one clue. We’ll come back to that in a moment.

Then, if you read my previous posts on ID-ing terns, you might remember that we need to look at the color of the legs and the bill. The tricky thing here is that the bill color changes according to the bird’s age and the time of year. The end of August is late enough that the birds have begun molting out of their breeding plumage, but to further complicate matters, not every bird molts at exactly the same time.

Still, we have to go with what we know. When this photo was taken, this bird had orange legs and a two-toned orange-and-black bill, and the dark head feathers are in back, reaching to the top of the head.

Now we turn to our field guide (or handy birding app). We’re looking for a species that matches our description of this bird.

Most terns have black legs, so the orange legs on this one exclude all but a few species. In North America, only Common, Arctic, Forster’s, and Roseate Terns have orange legs at some point. However, the legs on the Arctic Tern are extremely short (maybe to conserve body heat?), and this tern has normal length legs. (Besides, they have tiny black beaks.)That leaves three species.

Now, how about that fancy two-tone beak? Of these species, Common and Forster’s Terns have orange and black beaks. Roseate Terns get dark red at the end of the summer, but this beak is orange, not red. Too bad, that would have been an exciting sighting!

Now we look at the pattern on the head. Which tern has their head neatly quartered, with black on the top back quadrant, and white everywhere else? (Sibley calls this a “hindcrown.”)

Common Tern_JacksonLakeSP-CO_LAH_2197Yup, it’s a Common Tern. This too was a “good bird” to find in Colorado. If you look at the map in the field guide, you’ll see that they normally migrate farther to the east. However, we were birding in the far northeastern corner of the state, close to Nebraska, and  birds don’t have maps with state lines on them.

It was helpful that we saw this bird when we did. A few weeks later and both the orange legs and beak would have turned black, as in nonbreeding birds. Then we would have had to work much harder for an ID.’

Here is a picture of a Forster’s Tern, for comparison. You might notice that the legs are much brighter. This is likely a seasonal difference, as this picture was taken in North Carolina right around New Year’s. But also note the very different markings on the head. Unmistakable!

Forster's Tern_KillDevilHills-NC_LAH_LAH_2807

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One Response to Bird Quiz: Answer

  1. careymoonbeam says:

    I always enjoy your detailed ID posts. Thanks!

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