Date: 7/11/20 1:51 pm
From: Alvaro Jaramillo <chucao...>
Subject: Re: [southbaybirds] The Common Tern Continues at A16 on 7/11/2020

Just a word of caution on identifying these subadult terns. In my opinion, medium sized tern identification is among the most challenging of issues, specifically on these non-adult birds. A lot of the identification needs to be done by comparing structure to nearby known birds (Forster’s in this case). Some of the features that are typically associated with Common Tern, such as the darker outer primaries, and darker “carpal” bar can show up in one year old Forster’s Tern. Apart from structure, key is to look at the outer tail feather and assess if it is dark on the outer part of the feather (outside the shaft), or inside the shaft. Only Forster’s (well Snowy-crowned in South America is another), shows a dark inner feather vane, rather than outer. So far photos have been distant. But if anyone goes out there and really wants to drill down on this bird, that would be a feature to look for. I am not saying that it is not a Common Tern, I am saying that with these ages you need to extra cautious and look at some very specific stuff.

Take care, good birding, stay healthy.


Alvaro Jaramillo

<mailto:<alvaro...> <alvaro...>

From: <southbaybirds...> <southbaybirds...> On Behalf Of Frank Vanslager via
Sent: Saturday, July 11, 2020 10:55 AM
To: <southbaybirds...>
Subject: [southbaybirds] The Common Tern Continues at A16 on 7/11/2020


I decided to do a CCW walk around A16, hoping that a rarity might leap up and bite me. No such luck. However I did find the Common Tern at almost the same spot where we reported it on July 8. The upper right hand corner in this photo is the left edge of island 6 that Dave Weber reported in the background.

I'm a bit worried that the bird isn't moving. Today it wasn't even feeding.

Frank Vanslager

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