Thursday, October 4, 2012

Common vs Forster's Terns


A Common Tern gives itself a shakedown. Note the partial black "hood" extending all the way around the back of its neck, and bold carpal bar. Ormond Beach, Port Hueneme, CA.

Birders struggle with tern identification...it is a source of Fear and Loathing for beginner and veteran alike. Royal vs. Elegant, Black vs. White-winged, Sooty vs. Bridled, Common vs. Arctic, Common vs. Roseate, and perhaps most frequently of all, Common vs. Forster's. Here are a few shots and notes that could be helpful to tell immature birds of these two species apart. The process is frequently messy and not always a perfect match for field guides (which is their fault, not yours), but it can be done! As always, knowing status and distribution can provide some great hints, but anything can happen during migration.


Forster's Tern, with "earmuffs" that don't wrap around the back of the head. Common Terns never sport this kind of headgear. Poe Road, Salton Sea, CA.


A Common Tern conveniently shows off its outer tail feathers, which feature black on the outer webs. Ormond Beach.


A Forster's Tern stoops to catch a Tilapia. Check out the white/gray tail. This bird has extensive black in the primaries, which birders often assume is associated only with Common Tern. Poe Road.


One of my better Common Tern shots. Note how pale the primaries appear from this angle, which is not what birders expect...but everything else points exactly to Common, including the delicate bill. Taking tern pictures can be extremely frustrating, but when they suddenly bank to dive on a fish or other prey, it makes for a pretty sweet shot if you can catch it in time. Ormond Beach.




This is a pretty good quiz bird. There is black in the tail, but the outer retrices are clearly edged in white...this is a Forster's Tern. Poe Road.


Here's a pretty "typical" Forster's Tern, with earmuffs and pale upperwing. Also note the slightly longer and heavier bill. Poe Road.


Common Tern. Compare the underwing pattern of this bird with the above Forster's. Ormond Beach.


This Common Tern has a touch of yellow at the tip of the bill. Although not a frequently observed trait, it happens enough for a birder to think twice before you think you find an out of range or hybrid Sandwich Tern. Poe Road.

12 comments:

  1. Excellent work! I didn't know that Common Terns could have yellow on the tips of their bills

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    1. Thanks Scott. The yellow tip is relatively rare, but it does happen.

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  2. Nifty guide. This will be referenced time and again upon my return to the Salton Sea. I never made it to Poe Road, and that is a huge regret.

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    1. Thanks Laurence. Are you still lurking back there again this year?

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    2. Oh yeah I'll have to make it back once more in 2012

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    3. I've gotta check out this Poe Road...

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    4. Poe probably won't be so terny later in the fall, but if you get down to Brawley or the end of Vendel Road, its certainly worth a look.

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  3. This is wonderful and explains the differences so well!

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    1. Just doing what I think is best. Too bad I don't have a wealth of Arctic Tern shots (or any, for that matter) to use.

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  4. I am really enjoying these educational ID posts. Keep them coming. A great resource for beginner birders.

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    1. Thanks Jake. It took me quite a while to get the two species down, and I didnt even address breeding plumage birds...these things can be rough! A camera can definitely help when IDing these species.

      I'll get a pelagic post up next week, promise.

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  5. This definitely seems wicked helpful... Seriously do more of these posts.

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