Re: Elsie Roemer Terns

Alvaro Jaramillo
 

Hi Teale,
I think the mystery tern is a subadult Forster's Tern, maybe two years old? The reason is that the mask actually shows through as being darker than the nape in one photo. But more importantly in one of the photos (the second one), the longest tail feather shows a dark edge on the inner vane of the feather. This is unique in mid-sized terns in North America, all others show a dark edge to the outer vane. There is some odd dark on the base of the tail, but I am ignoring that, as the dark inner vane on the longest feather is so key. Common Terns at this age often also have the dark on the leading edge of the inner wing (patagial/carpal), although it is less consistent by the second year.
Good birding,
Alvaro

Alvaro Jaramillo
alvaro@...
www.alvarosadventures.com

-----Original Message-----
From: EBB-Sightings@groups.io <EBB-Sightings@groups.io> On Behalf Of Teale Fristoe
Sent: Monday, August 19, 2019 10:12 PM
To: EBB-Sightings@groups.io
Subject: [EBB-Sightings] Elsie Roemer Terns

Hello,

Today I went back to Elsie Roemer Bird Sanctuary. After looking unsuccessfully for rare shorebirds with Noah Arthur, I started examining terns. There were far fewer today than there have been my past couple of visits, with just one Least, two Elegant, a handful of Forster's, and no Caspians. But there were a couple of interesting individuals present.

The first was an adult Common Tern, which was fairly cooperative and stood next to a Forster's, allowing close comparison of legs and bill. It apparently had not started molting and had a complete black cap and nape.

I'm still not sure on the species of the other individual, and I welcome any thoughts you may have. It first struck me as a juvenile Common because it has black outer tail feathers and a black nape, but the wing pattern doesn't look right for a Common. I then thought it might be a stray Arctic (hey a guy can dream, right?), but the bill looks too big for that. It also appears to be molting, which I believe only an adult would be doing at this time of the year. So I now think it's probably a Forster's, though I don't know how to explain the outer tail feathers.

Photos and a complete list can be seen on ebird.
https://ebird.org/view/checklist/S59118513

Again, I'd love to hear feedback on the id of the mystery tern if you're so inclined.

Happy migration,
Teale Fristoe
Berkeley




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