Roseate or Common Tern (Fort de Soto, Florida) (1 Viewer)

[Mark Eising]

The tern on the left looks very much like a Roseate Tern but I am not sure.
The one on the right looks like a Common Tern, but, other than the color of the bill, does not seem to differ from the one on the left.
Any suggestions?
I took the photo on 31 March 2022 at Fort de Soto, Florida.

 

[THE_FERN]

I don't think either are roseate terns. They would have thinner more uniform black bills [not strong gonydeal angle as here]. Tails should project far past wingtips [again not as here]. The strong bills make me suspect both are Forster's terns but the mantle and primaries are quite dark. So I think these are both common terns. Back one is sandwich of course.

 

[pianoman]

Hmm left one looks OK for Roseate to me. A Roseate bill is larger as well as being all black. Also, the visible area around the breast and throat is a purer white than one would normally see on Common.

 

[THE_FERN]

Hmm left one looks OK for Roseate to me. A Roseate bill is larger as well as being all black. Also, the visible area around the breast and throat is a purer white than one would normally see on Common.

Comparing with here:

Roseate Tern - Sterna dougallii - Media Search - Macaulay Library and eBird

Suggests cf left op bird roseate bill is thinner and longer with gonydeal angle in a slightly different place. (All-black billed common terns are quite common in the US I believe). The mantle is clearly darker than in the Macaulay images

Edit: note also the much longer tails in the Macaulay images

 

[Mark Eising]

Thank you all for helping me. I am still not certain. I also tend to think both are Common Terns, mainly because both don't have long tailfeathers.

 

[Butty]

If feathers are longer than in the competing alternative, that's an ID feature. If feathers aren't longer than in the competing alternative, that's an not ID feature.

 

[lou salomon]

Adult Roseate would have obvious broad pale fringes on inner webs to outer primaries which the bird in question clearly lacks. It's a Common Tern.

 

[THE_FERN]

If feathers are longer than in the competing alternative, that's an ID feature. If feathers aren't longer than in the competing alternative, that's an not ID feature.

? This statement requires a lot of qualification I think...

Otherwise you could never use short feathers as an id feature but of course you can.

Perhaps the aim is to suggest that the tail feathers in the left most bird are in someway unrepresentative of final, adult state. They look pretty well developed to me

 

[Butty]

? This statement requires a lot of qualification I think...
the tail feathers . . . look pretty well developed to me

Well done 🎖️ You've provided a specific qualification to my general statement which then makes the use of feather-length acceptable in this case

 

[Mark Eising]

Thank you all for your help and comments! It helped me a lot and I have appreciated it very much. I will consider both terns Common Terns.

 

[SteveClifton]

Thank you all for your help and comments! It helped me a lot and I have appreciated it very much. I will consider both terns Common Terns.

Is Forster's Tern a possibility in your area?

Having checked maps online it seems to be. Hence the following seem to point to F's Tern:
Clean white underparts
Deep-based black bill (transitioning to summer plumage, black is no problem)
Large wedge of white between the bill base and black cap.
Long orange-red legs

A few other features also point to Forster's. I found one or two other images of early spring birds with dusky-shaded tertial centres (secondaries too-so bird on left perhaps a 2cy or 3cy?). The bird on the right does seem to have some grey feathering underneath (shading due to wind?) but importantly the lower breast, belly and flanks all look clean white.

Could the lack of long tail streamers be age-related?

 

[THE_FERN]

Is Forster's Tern a possibility in your area?

Having checked maps online it seems to be. Hence the following seem to point to F's Tern:
Clean white underparts
Deep-based black bill (transitioning to summer plumage, black is no problem)
Large wedge of white between the bill base and black cap.
Long orange-red legs

A few other features also point to Forster's. I found one or two other images of early spring birds with dusky-shaded tertial centres (secondaries too-so bird on left perhaps a 2cy or 3cy?). The bird on the right does seem to have some grey feathering underneath (shading due to wind?) but importantly the lower breast, belly and flanks all look clean white.

Could the lack of long tail streamers be age-related?

You'll see why I didn't go with that idea

 

[SteveClifton]

You'll see why I didn't go with that idea

Can you be more specific?

 

[THE_FERN]

Can you be more specific?

See first reply in thread

 

[SteveClifton]

See first reply in thread

Ok, yes I saw that. However, I usually expect Common Terns to look noticeably darker when side by side with Sandwich Tern. The bird on the right looks similar in tone, and the one on the left just a tad darker, but it's not as striking a difference as you'd expect between Common and Sandwich.

I'm a little wary of judging grey tones accurately from photos-they can appear darker than in reality, but conversely they can also look much paler. Yet I keep coming back to the apparent lack of contrast with the Sandwich Tern (actually now Cabot's Tern!)
The grey-centred tertials are another thing that don't appear to fit Common (but typical of imm Forster's). Likewise the very white underparts.
The primaries don't look so strikingly pale as we'd expect for adult Forster's, but from my reading, 2cy (and perhaps also 3cy) would have darker grey primaries than adults. They just don't appear as dark as I'd expect for Common Tern! and interestingly, they all appear to be of the same generation (Common usually show obvious contrast between outer and inner primaries).

I considered that 2cy Common might not develop the pale grey breast and belly, and presumably this could also apply to transitional adults. However, 2cy Common Tern would also very likely show the remnants of a darker carpal on the folded wing. Neither bird here has that.

Would like to see other images if they exist...? but for now I'd favour Forster's. I'm slightly less certain of the bird on the right.

 

[KC Foggin]

Common Tern for me.

 

[smiths]

As Steve Clifton wrote, both of these birds are Forster's Terns, for the reasons he outlined.
Nothing to add really, other than that the white spotting on the crown of these birds reaches further back towards the nape than what is usually seen in moulting Common Tern and that the base of the wingtip of these birds looks clearly paler grey than the wing coverts, almost whitish even.
In Common Tern, the wingtips typically look slightly darker than the wing coverts.

 

[Rick Mundy]

Forster's Tern on the left for me too (can't see the closer one very well). Based mainly on the uniform primary tract which is completely wrong for either adult Common Tern or adult Roseate Tern; also bill size and shape, leg length and colour. I'm confused about the tail streamer conversation, what is the problem there?

 

[Mark Eising]

Wow, I didn't expect so many conversations on these terns! Very interesting! Thank you all so much!