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Tern ID Query (1 Viewer)

Bluetail

Senior Moment
I noticed this rather nice photo that Searobin has just posted in the gallery:

http://www.birdforum.net/pp_gallery/showphoto.php?photo=56550

It's labelled as a Forster's Tern and I'm certainly not qualified to argue with that. However, in view of the extent of the black on the bill tip, the not obviously "silver" primaries and the dark outer primaries I did find myself wondering why it's not a Common Tern (which I think isn't altogether impossible in New Jersey). So how do you go about sorting out the ID of a flying Common versus a Forster's?
 

Michael W

Mountain Chickadee
Good catch, Jason. I also think it's a Common Tern. The red bill with a black tip (vs orange w/ black tip) and darkness on primaries (vs silvery-white) point to Common.

Michael
 

searobin

Well-known member
I have a hard time with Forster’s and Common Terns so will be following this post with interest.

Thanks Bluetail.
 

njlarsen

Gallery Moderator
Opus Editor
Supporter
Barbados
I agree on common, but have one additional question: my old trusty Natl Geographic mentions that Forster's has a white rump in contrast to both back and tail, both of which are light gray -- except for tail edges that are white (common and arctic both white in tail). Sibley mentions this with text next to only one of the drawings but does not show it, so has this been discredited as a field mark?

thanks
Niels
 

JANJ

Well-known member
njlarsen said:
I agree on common, but have one additional question: my old trusty Natl Geographic mentions that Forster's has a white rump in contrast to both back and tail, both of which are light gray -- except for tail edges that are white (common and arctic both white in tail). Sibley mentions this with text next to only one of the drawings but does not show it, so has this been discredited as a field mark?

thanks
Niels

No, it hasn´t been discredited as a field mark, but due to the light upperparts the contrast is often hard to observe. On Forster´s outermost tailfeather, the outer web is white and the inner web is dark, thus the opposite in Common and Arctic. In the second image, of the two Common Terns in this thread it´s well seen as a dark line on the tail edges. It´s often quite visible in good photos, but often less so in the field. The pale (fresh) silver-grey primaries, gleaming white flash, is a better fieldmark.
JanJ
 

Grousemore

Senior Member
I've seen some potentially confusing Forster's (second summer for instance) recently.
Interesting reading, thanks, Jan.
 

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