Achrocephalus or Sylvia borin? (1 Viewer)

[Richard Dale]

Nope - it's impossible to do more than guess at the tail-tip-shape, though certainly it's not obviously rounded. But obviously I'd never tell someone that what they think they can see isn't actually there...

Hi Butty, what I mean by rounded tail shape isn't as literal as you are taking it. I don't mean the tail appears rounded in the images. I mean we can infer from what we see in the first photo that the tail must be rounded in shape: in the first photo we can see that the two outer tail feathers are clearly shorter than the rest of the tail. The foreshortening of the image makes it harder to draw conclusions beyond that, but when the outer tail feathers are shorter than than the inner feathers, that means the bird has a rounded tail shape (when spread) and this is character of Acrocephalus warblers.

A garden warbler has outer tail feathers the same length as the rest of the tail. On the closed tail viewed from below the outer feathers completely cover the rest of the retrices, and the tail shape is square, for want of a better word.

Simon raises the possibility of it regrowing tail feathers, but neither reed/marsh or garden generally moult the tail in autumn, either as adults or juveniles, apparently with the very rare exception of the occasional adult garden warbler (not something I've ever seen in many hundred of birds in the hand). To be regrowing both its outer tail feathers it would have to have lost just these feathers somehow (if it had lost the entire tail all the feathers would be the same length while regrowing).

Having said all that, hopefully, whether or not you concede my point regarding my interpretation of the tail from the first photo, you do now accept that it is clearly an Acrocephalus based on the videos and stills now posted (and therefore it does have a rounded tail). The most anomalous feature, the blue/grey legs, are at the extreme end of variation, and better for 1cy fuscus RW than MW (the lack of any feather wear means it has to be a 1cy bird, and in RW/MW, young birds tend to have darker, greyer legs than adults, and RW tend to have darker legs than MW).

 

[Butty]

the two outer tail feathers are clearly shorter than the rest of the tail

I would say so much shorter as to appear unnatural for a bird not in moult. Thus, these outermost feathers can't tell us anything about the natural shape of the tail-tip. Thus we don't know whether or not it's graduated.

neither reed/marsh or garden generally moult the tail in autumn, either as adults or juveniles, apparently with the very rare exception of the occasional adult garden warbler

Well, I'd have to drag BWP down off the shelf, but... Really? I'm confused. So, you mean the complete adult post-breeding moult is in summer sometime rather than autumn? Maybe you mistyped something.

 

[KenM]

Still looks like an acro here. Jizz looks better for one, upperpart plumage tones fit better (some pretty warm tones visible). Tertials are well marked (not good for garden warbler/good for marsh warbler) and emargination on P3 is strong (good for an acro, with position favouring marsh).

Well marked tertials?
I normally associate that comment with darker contrasting inners against pale edged “outers” something I’m not seeing here.
All you appear to have is paler “light” reflection off the edges no more or less than you might see from any other concolourous passerine.
Indeed if you look at image 2 in my last post. that really has contrasting tertials.
Am not seeing that comment justified here, regarding emargination on p3, that may be helpful, albeit I’ll need clarification on that point in lit.going forward.

 

[Mark Lew1s]

If you scroll slowly through the video you can see that the tertials are consistently dark centred with rather neat pale edges.

 

[KenM]

As a general comment regarding “movement” jizz, it was so brief, it was barely discernible as an aid to separating an Acro from anything else.
Clearly I’ve been reading the wrong “comics”over the years, never having seen lead grey legs attributed to Reed/Marsh, I must learn to keep up to date with the “latest” offerings.

If you scroll slowly through the video you can see that the tertials are consistently dark centred with rather neat pale edges.

would you say that they were more “contrasty” than my image 2?

 

[Mark Lew1s]

There’s plenty of useful jizz in 7 seconds worth of video. 7 seconds is a pretty long time to look at a warbler!

As for your Garden warbler pic, I’d say no, the tertials look more contrasty in your photo. But I’d also say that your photo is so poor there’s very little value to be gained from making the comparison. We all know a garden warblers tertials don’t actually look like that.

 

[Richard Dale]

I would say so much shorter as to appear unnatural for a bird not in moult

No, perfectly normal for a reed (or marsh) warbler, unless every one of the 300+ RW I handle each year are all just completing the moult of their outer tail feathers. The outer tail feathers are several millimeters shorter than the central ones in these species. The bird is not in tail moult.
One of the first things I show a trainee ringer on the relatively rare occasions when we catch a GW and they inevitably don't know what it is, is the tail shape to rule out the plain Acrocephalus and Locustella species.

Really? I'm confused. So, you mean the complete adult post-breeding moult is in summer sometime rather than autumn? Maybe you mistyped something.

Yes, really. Neither species, with the exception of a very small proportion of GW, has a complete post-breeding moult. Adult RW technically has a partial post-breeding moult, but rarely replace more than a handful of body feathers. Adult GW has a variable partial post-breeding moult, usually more extensive than in the post-juvenile moult of 1cy birds, though a very small proportion of birds have a more extensive moult which includes some (and apparently in very rare cases all) flight feathers. Adults and young of both species have a complete pre-breeding moult in the winter.

 

[KenM]

There’s plenty of useful jizz in 7 seconds worth of video. 7 seconds is a pretty long time to look at a warbler!

As for your Garden warbler pic, I’d say no, the tertials look more contrasty in your photo. But I’d also say that your photo is so poor there’s very little value to be gained from making the comparison. We all know a garden warblers tertials don’t actually look like that.

Here’s another marginally better image of Garden Warbler…

 

[Butty]

Here’s another . . .

Which particular one of the ID points discussed above does this illustrate?

 

[KenM]

Which particular one of the ID points discussed above does this illustrate?

Pale edges to the tertials?