Mystery Gull Identified as 2nd-cycle Thayer's Gull

Seward, Alaska

On Sunday, an odd-looking gull was careening around with the others, vying to find or steal herring. 

I couldn’t figure out what it was, and so sent my photos to Steve Heinl, the gull guru in Ketchikan. Here’s his analysis and verdict:

Bill size: 

“I think your bird is a 2nd-cycle Thayer's Gull - sometimes it's hard to judge bill size without direct comparison to another gull, but the bird's bill looks considerably slimmer than the bill on the Glaucous-winged Gull in the background.

Outer primaries: 

It has two-toned outer primaries, meaning that the outer webs of those feathers are dark and the inner webs are much paler, and the undersides of the outer primaries are dark only on the tips of those feathers - all very good for Thayer's Gull. 

Compared to Herring Gull: 

The outer primaries are not blackish like they would be if it was a Herring Gull, which also would show more extensive dark on the undersides of the primaries.  

Compared to hybrid: 

I think if the bird was a hybrid Glaucous-winged x Herring gull, the bird's bill would be stouter or thicker.  It can be quite difficult to judge that, though.  I have to admit that I see a lot of birds in Ketchikan that I'm not sure about, but usually they are on the larger side and have darker primaries.”

Thank you, Steve! Gulls are challenging and fascinating simultaneously. It’s so great to be able to share my photos and get a quick analysis and ID. It’s also good to know that gull identification can be challenging to experts too.

Happy Birding!

Carol Griswold

Seward Sporadic Bird Report Reporter