Unstreaked Acro in London..... (2 Viewers)

[KenM]

Putative fuscus re-visited.

Charles Hi,

Having put a lot of time into this exercise, I'm now of the opinion that a change of tack (re-assessment) might be more prudent.
This bird has certainly become a ''real'' learning curve for me, principally because of the pallor, and the seemingly long pp which in no small way had a major influence, in sending me down the fuscus road.

Also not helping in this instance, was sustained exposure to a contender ''classic'' BRW during Oct.2001, which couldn't have looked more different, ie. olive grey uppers, grey tarsi and a c50% pp to tertial ratio. Comparing ratios it would appear (depending on what you read) that e.g. BRW's pp ratio can be between one and two thirds of overlying tertials, compared to Marsh/Reed which are between 65-100%. If images are anything to measure against, then this two thirds maximum might have even greater flexibility if the ''variable'' cosmetics are anything to go by?

Having taken many shots over the period, and subsequently found a number of features that perhaps at best, might be considered questionable regarding Caspian Reed Warbler as a putative candidate.
Firstly, the Iris colour appears to be contrastingly grey in most images, this would seem to be at odds with all Reed Warbler images that I have trawled on the web (mid-dark brown, being the principal colour throughout), although a couple of BRW's looked to have a paler Iris.

Secondly, the general concolourousness of the upper-parts might also, not be helpful for A.scirpaceous, perhaps more akin to BRW?
The bare-parts colouring ie. lower mandible, legs, toes and claws!, appear to exhibit a strong yellow wash in most lights, again perhaps not really compatible with Reed, A.scirp., although contrary to most text, certainly appears to be seen occasionally on BRW?

The bird also appears to show better in some images than others, a smaller emargination on p4 (further down the wing) as well as p3, this as I understand it, can be compatible with Casp.RW/BRW...whilst excluding RW.

Charles as you have suggested that a Marsh/BRW hybrid might be a candidate? possibly explaining it's apparent wing length and current Wintering site, at a ''lost'' point between Africa and India...far fetched and unlikely perhaps?

Further on, the moulting period for RW generally runs between early Oct-early Nov. and later for BRW and Caspian (leading up to, and just before Spring departure), perhaps time might tell?

Cheers

 

[CharlesFentiman]

Hi Ken

This bird has indeed been an intriguing individual and you have done a great job of gathering so many images of this bird and hopefully it will stay long enough to get some fresh plumage which might help but for now we have an individual that seems wrong for the usual suspects. Although Caspian Reed Warbler still seems a possibility and perhaps it will yet deliver a suitable package of DNA in a collectable position we should consider the possibility it being a hybrid. Looking at various items of literature, photos and web based information it seems that Marsh x Blyth's reed pairings do occur in Finland but as far as I can make out the offspring from such pairings have not been recorded with certainty away from the breeding areas, although several have been suspected in the UK.

By carefully recording the birds features we do at least have a solid description of the bird but the feather wear is a problem, but who knows, that might change. But on what we have so far I struggle to see this bird as a Western European Reed Warbler and it does seem to be an amalgam of Marsh and Blyth's features but it would be useful to know if there have been any recorded definite hybrid's and what they looked like?

Cheers

 

[KenM]

FWIW I seem to recall the 2007 "Chinatown" mystery Acro as having a contrasting grey Iris, pale tarsi and seemingly white underparts?

Cheers

 

[Brian J Small]

Ken.

There are some major inaccuracies in your comments in post 61.

Iris colour is largely an age-related character, and one that cannot be used as a feature for differentiating between ERW (scirp.or fusc.) and BRW. If it seems grey then it is likely a young bird.

“The bird also appears to show better in some images than others, a smaller emargination on p4 (further down the wing) as well as p3, this as I understand it, can be compatible with Casp.RW/BRW...whilst excluding RW.”
Not true.

“Further on, the moulting period for RW generally runs between early Oct-early Nov. and later for BRW and Caspian (leading up to, and just before Spring departure), perhaps time might tell?”

Nonsense. Juvenile Acrocephalus of those discussed here retain their wing and tail feathers throughout the first year – only in a few Acro is post-juvenile complete. Therefore you will have to wait a long time as this seems to be a young bird. Adult ERW in western Africa have a complete moult Sept-Dec, but many in Uganda (fuscus) moult Dec-Feb. Marsh moult Jan-Mar. BRW and ERW have moult timings basically the same (Sept-Dec)

Has this bird not been heard to call? When I see BRW in India and elsewhere they are always calling…

Your last few images have a very green cast and are not showing the true colour. That it seems concolorous is true, but most of the images indicate that is is a Reed Warbler.

Brian S

 

[KenM]

Ken.

There are some major inaccuracies in your comments in post 61.

Iris colour is largely an age-related character, and one that cannot be used as a feature for differentiating between ERW (scirp.or fusc.) and BRW. If it seems grey then it is likely a young bird.



“The bird also appears to show better in some images than others, a smaller emargination on p4 (further down the wing) as well as p3, this as I understand it, can be compatible with Casp.RW/BRW...whilst excluding RW.”
Not true.

“Further on, the moulting period for RW generally runs between early Oct-early Nov. and later for BRW and Caspian (leading up to, and just before Spring departure), perhaps time might tell?”

Nonsense. Juvenile Acrocephalus of those discussed here retain their wing and tail feathers throughout the first year – only in a few Acro is post-juvenile complete. Therefore you will have to wait a long time as this seems to be a young bird. Adult ERW in western Africa have a complete moult Sept-Dec, but many in Uganda (fuscus) moult Dec-Feb. Marsh moult Jan-Mar. BRW and ERW have moult timings basically the same (Sept-Dec)

Has this bird not been heard to call? When I see BRW in India and elsewhere they are always calling…

Your last few images have a very green cast and are not showing the true colour. That it seems concolorous is true, but most of the images indicate that is is a Reed Warbler.

Brian S

Welcome aboard Brian,

Regarding the Iris colour, I did wonder whether the paler Iris might be age related, it seemed perhaps coincidental, that I could only (on the few that I could find) appeared to show only on BRW.

Concerning emargination on p3 and p4, I may have misconstrued in the lit. but I thought there was an inference that ERW does not normally show a second e.point on p4, and that it was more likely on BRW and fuscus.

Your suggestion that it is probably a 1st year bird seems to be at odds with the norm regarding immature ERW, as lit. (and my personal observations), indicate that birds of this age show a richer buff wash to the underparts, with stronger rufous washed uppers, also sporting darker contrasting centred tertials, which is diametrically opposite to the cosmetics on the Leyton bird.

Indeed a number of earlier posters (self included) did consider Marsh Warbler as a candidate, no doubt the pale uppers. and silky white unders. contributed to that original notion.

It has been heard to call...but not by me.

I've never been to India, but I have experienced over a three week period (almost on a daily basis) the Canary Wharf 2001 BRW, and that called circa 6 times (once only) over as many seconds during it's period of confinement.

I don't see the ''green cast'' at all, apart from one image where it was in the shadow of a leaf, whilst on the ground. However in direct light, I can see no olive-y tones.

At least we have agreement on it's concolourousness (which in itself is not a strong recommendation for ERW?).

Any further comments will be most welcome.

 

[wolfbirder]

I certainly got the impression that iris colour of BRW seen in UK, and in Finland for example were paler than ERW. It was simply a notable feature that I picked up by examining lots of images of both.

But obviously I am not questioning Brian. I know which division I'm in and its not high :smoke:

Its a very interesting bird Ken, almost tempted to try to see it if it's still around after Xmas. Good work!

 

[KenM]

I certainly got the impression that iris colour of BRW seen in UK, and in Finland for example were paler than ERW. It was simply a notable feature that I picked up by examining lots of images of both.

But obviously I am not questioning Brian. I know which division I'm in and its not high :smoke:

Its a very interesting bird Ken, almost tempted to try to see it if it's still around after Xmas. Good work!

We are ALL in the same division Nick, particularly so when we are dealing with an acutely variable taxa, not just cosmetically, but biometrically as well. :t:

 

[Bismarck Honeyeater]

As mentioned up thread, I heard it call on the day it was found. Sounded like 'tchurr' heard 2-3 times. Seen it once since and nothing more heard.

 

[Jane Turner]

As mentioned up thread, I heard it call on the day it was found. Sounded like 'tchurr' heard 2-3 times. Seen it once since and nothing more heard.

Which would rule out either MW or BRW

 

[Jane Turner]

Concerning emargination on p3 and p4, I may have misconstrued in the lit. but I thought there was an inference that ERW does not normally show a second e.point on p4, and that it was more likely on BRW and fuscus.

Its quite common for birds in very worn plumage to show a weak emargination on the feather inside the one that is emarginated - due to differential wear on the exposed parts of the inner feather

 

[Brian J Small]

"I don't see the ''green cast'' at all"

Yours on left, adjusted on right.

Brian

 

[Bismarck Honeyeater]

Which would rule out either MW or BRW

I would think it rules in Reed Warbler

 

[KenM]

"I don't see the ''green cast'' at all"

Yours on left, adjusted on right.

Brian

And here is an even greener example....plus the norm, also a more sandy shot. (all straight out the camera...without any photo manipulation). Clearly the frond luminescence on the feathering alters with the ambient lighting, as an illustrator you should appreciate how lighting can alter perceptions, ''particularly'' with subtle browns, greys and olives.

 

[KenM]

As mentioned up thread, I heard it call on the day it was found. Sounded like 'tchurr' heard 2-3 times. Seen it once since and nothing more heard.

I can't comment on the ''churr'' note, other than this call is not infrequently used by Common Whitethroat?...If you saw the bird open it's bill and ''churr'' then so be it.

I went today, didn't see any CW, but I thought I heard several ''tacs'' emanating from the bramble below?...however I may have been mistaken, lots of traffic noise etc?

 

[dbradnum]

I can't comment on the ''churr'' note, other than this call is not infrequently used by Common Whitethroat?...If you saw the bird open it's bill and ''churr'' then so be it.

I went today, didn't see any CW, but I thought I heard several ''tacs'' emanating from the bramble below?...however I may have been mistaken, lots of traffic noise etc?

On my one and only visit to see this bird, I also heard it giving a standard Reed Warbler call at close range - no doubt about which bird was calling.

 

[Bismarck Honeyeater]

I can't comment on the ''churr'' note, other than this call is not infrequently used by Common Whitethroat?...If you saw the bird open it's bill and ''churr'' then so be it.

I did.

Presumably 'fuscus' is not ruled out by this. Let's all look out for poo��

 

[Jane Turner]

I'm not sure if anyone has done a study to see if there is anything subtle in the call note of fuscus - but it has the same double starting note as Western birds.

Happy Christmas btw


edit: there were no def fuscus calls on Xeno canto when I looked just now

 

[Motmot]

"Nonsense. Juvenile Acrocephalus of those discussed here retain their wing and tail feathers throughout the first year – only in a few Acro is post-juvenile complete. Therefore you will have to wait a long time as this seems to be a young bird."

I don't think this is correct at all. RWs, MWs and BRWs do not retain juv wing and tail feathers throughout the first year afaik.

 

[Brian J Small]

"Nonsense. Juvenile Acrocephalus of those discussed here retain their wing and tail feathers throughout the first year – only in a few Acro is post-juvenile complete. Therefore you will have to wait a long time as this seems to be a young bird."

I don't think this is correct at all. RWs, MWs and BRWs do not retain juv wing and tail feathers throughout the first year afaik.

You are right and I eat humble christmas pie, they do indeed have a complete moult from oct-dec., too much watching gulls. but we still may have along wait until this bird renews its remiges?

B

 

[Bismarck Honeyeater]

Saw, and heard it spontaneously calling, again today, still sounds like a Reed Warbler. Perhaps a bit more of a rolling 'Tchrrur' this time. Looking a bit smarter than the last two times I have seen it, maybe it has finished moulting?

Tried a bit of playback with both calls and song of BRW and ERW. Nada, zip, zilch, though the Stonechat, Wrens and Grey Wagtails enjoyed it, Rats didn't seem too interested either.