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Subject: [Tropicbirds] Immature Tropicbird sp. 鸏 [Print This Page]

Author: cchristina Time: 4/05/2008 18:58 Subject: Immature Tropicbird sp. 鸏

2008.5.4

Southern Waters of Hong Kong

Thanks Tung for leading this amazing trip and Thanks Geoff, Richard and Mike for finding and identifying this HK First! And special thanks to the Tropicbird for showing up!

Author: Tony Time: 4/05/2008 19:16

So exciting!

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Author: wleepoin Time: 4/05/2008 19:46

Southern Waters of Po Toi
4May08

Yet again, an excellent boat-trip!! So happy, thanks for all birders & "bird".

Cheers
PWMK

Author: hpippen Time: 4/05/2008 20:15

:shock:

:shock:

Thanks Tung & all the experts!

Author: cjacky Time: 4/05/2008 20:17

2008.5.4

Southern Waters of Hong Kong

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Author: HFCheung Time: 4/05/2008 20:20

This is definitely a White-Tailed Tropicbird. Please wait a while for me to tell you the evidence. Thanks for the photo.

HF Cheung

Author: oLDcaR Time: 4/05/2008 20:38

Thanks Tung, Geoff, Richard and Mike! We have a exciting boat trip today!
Southern Waters of Po Toi
4 May 08

Author: cgeoff Time: 4/05/2008 20:43

Identification of immature tropicbirds is tricky, but my thoughts are as follows:

1. Not Red-billed due to the lack of black nape collar.

2. Not Red-tailed as this species has rather coarsely, darkly and densely barred upperparts extending onto the crown and nape. This is obvious on the only immature Red-tailed photo currently on the Oriental Bird Club images website:

http://orientalbirdimages.org/search.php?action=searchresult&Bird_ID=1074&Bird_Image_ID=5265&Bird_Family_ID=&p=7

Further, while sizeable, the bird today did not appear to be as large and bulky as Red-tailed is supposed to be.

3. This leaves White-tailed, which has the least white in the wing of the three species in immature plumage, based on the illustration in Rasmussen and Anderton (Birds of South Asia). Peter's photos show well just how little (I did not see this in the field as it was flying away from us). Further, the barring in this species is described in the same guide as 'fine, widely spaced', which fits the bird today. The bill is stated to be 'dusky-yellow'; although Red-tailed may have this at some time in its progression to adult plumage, it seems to be standard for White-tailed.

I believe on range White-tailed is the most likely.

Geoff

Author: HFCheung Time: 4/05/2008 20:53

One can refer to the Bird of the Indian Subcontinent, by Richard Grimmett, Coral Inskipp and Tim Inskipp. White-tailed Tropicbird has smaller bill compared to the other two Tropicbird species. A juvenile White-tailed Tropicbird has pale yellow bill. It has several black primaries at the wing tip. In comparision, Red-billed Tropicbird has much more black primaries at the wing tip, while Red-tailed has grey or black bill and no black primaries.

HF Cheung

Author: Carmen Time: 4/05/2008 21:01

Thanks tung, all the experts and the bird!

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Author: cthomas Time: 4/05/2008 21:25

Thanks for all expert to find this in the sea...

4/5/2008
Southern Water of HK 香港南區水域
Leica 800mm + 20D
ISO200 f8 1/1600s

Author: lmichael Time: 4/05/2008 21:53

Well done all the photographers - and the photos are going to be very important because this is a very difficult bird.

I see why others have gone for White-tailed and they might be right, but...

I am not convinced that any of the text descriptions in field guides are very accurate as there is very little published primary data out there (actually surprisingly little for such widespread species).

Instead of looking at field guides I have done a net search for photos. This wasn't very productive but was enough to convince me that bill colour of non-adults is (a) variable, (b) little understood except in Red-billed (c) blackest in fledglings and becoming paler later. The key point was that the photos which I looked at provided limited support for the comments on bill colour in Harrison.

I did also find one web site which discussed id from Don Roberson who is a Californian seabird expert http://montereybay.com/creagus/tropicbd-id.html

This gave me the best match for our bird - not the first four in the paper but the Red-tailed photo which comes after the specimen photos. Note the black leading edge to outer 3 or 4 primaries.

Also note how extensive black is on the primaries in (all?) White-tailed photos, admittedly mostly adults. Now, this could increase with age but I find this counterintuitive: in most largely white seabirds (actually most white waterbirds) the amount of black decreases with age [there is a reason for this, white plumage wears more quickly but is more conspicuous and hence is relatively more advantageous for adult birds]. White-tailed Tropicbird could show a different pattern but unlikely I think.

To sum up I think that bill colour on our bird was within the range for both Red and White-tailed (but not Red-billed) and extent of black on primaries matches at least one Red-tailed photo (albeit more than I would have expected from published texts) but is not extensive enough for White-tailed. I haven't found any other plumage features which help - overall extent of black fringes to body feathers is going to be dependent on age and wear for example. Bill structure might help - I think it is heavy (which supports Red-tailed) but not obviously so.

At the moment I wouldn't like to call this one definitively and I think that we might need skin examination but my opinion for now is (still) Red-tailed.

Great bird!

Mike

Author: lmichael Time: 4/05/2008 22:34

Correction to link

If anyone wants to follow the link which I posted I am sorry for mispelling, should be;

http://montereybay.com/creagrus/tropicbd-id.html

Note extra r in creagrus

Sorry for any inconvenience.

Mike

Author: hooooon Time: 4/05/2008 23:12

I am very happy that I could witness this important record with all of you. So I can share my photos with you.

Author: Allen Time: 4/05/2008 23:38

4/5/2008
South Waters of Hong Kong

Many thanks to Tung, Fai Gor, Mike, Geoff and Richard.

Author: hkinni Time: 4/05/2008 23:44

It such a great day to me, Thank you Ah Tung and all the experts

Southern Waters of Po Toi
4 May 08

Author: tmichael Time: 4/05/2008 23:45

Having finally cleared family duties I've had a few minutes to look into this and must say that I strongly agree with Mike Leven's views on this bird.

Roberson's material seems much more authoritative than the Indian field guides - tropicbirds are definitely NOT Pamela Rasmussen's first love and when you look at the text it is rather thin, simplistic and in places odd - talking for example of a 'short rounded' tail in Red-tailed, which is not borne out in the plates (having said that though I think her text still favours id as Red-tailed).

The bill of this bird in my view most closely resembles that of Red-tailed, and in no way resembles that of White-tailed - see Roberson's photos of actual specimens.

Moreover, Roberson states:

Upperwing patterns are diagnostic. At all ages (my emboldening), Red-tailed Tropicbird has virtually all-white remiges (primaries and secondaries) so they look essentially "white-winged" in the field. This works both on quite young birds and older individuals up through adults. This is easy! ...the outer primaries on some Red-tails have black shaft streaks, and some tertials have black centers, but these are very fine points. All Red-tails appear essentially white-winged in the field."

This bird was thickset in my view, resembling a booby when it first landed on the sea at great distance, then, after I'd called it as tropicbird, making me think I'd lost it and picked up an egret so white-winged was it.

I think it very closely resembles the photo at the end of Roberson's paper which he identifies as an immature Red-tailed of around 30 months, which one would apparently expect to assume full adult plumage in a further 12 months.

It's late now, and I just lost a first version of this, so I hope it makes a little sense - and of course we will need to refer these images to overseas experts, I think, to get a definitive id.

Mike Turnbull

Author: kmatthew Time: 5/05/2008 00:42

WOW!!Tropic bird in HK??!! What a dream come true to me!! :shock: ...though I am not here to witness this amazing event...

I won't go into what species this is...as I have no idea even after looking at juv. photos of both species!! But great record never the less!! Congratulations to all photographers and birdwatchers who saw this amazing bird!!

Author: tmichael Time: 5/05/2008 06:22

I contacted Don Roberson, and he has responded immediately, but only after a couple of hours of careful examination of our and his own photos that he believes this is indeed, juvenile White-tailed.

I shall post his reasons in full this evening, but essentially the amount of dark webbing on the outermost primary, which always seemed problematical, is crucial.To quote Don:

... Gould, King & Sanger (1974) describe the outer remiges of juvenal-plumaged Red-tails as having "a black suffusion spreading into the vanes, both dorsally and ventrally, the the black dorsal shafts of the larger primaries, EXCLUDING THE OUTERMOST" (my emphasis). That means that the outer primary should be all-white even on juvenal Red-tails. Only the shaft is dark. On my flight shot of the juvenal Red-tailed below, which I've blown up and lightened and added contrast, you can see that the outer primary is all white and that the dark suffusion onto the vanes is interior to that, on penultimate remiges. On the close side view, only the shafts look dark.

The Hong Kong bird clearly has an entirely black outer web of the outermost 2 primaries; and some black on the outer web of P8 and a spot on the outer web of P7. None of these black outer webs reach the tip of the feather, which is white. This is a White-tailed pattern; I found a shot on line from the eastern U.S. -- in the Atlantic -- that is fairly similar at
http://www.patteson.com/images/wttr2-27.jpg
except that it has more black on P8 and P7 than the Hong Kong bird. But presumably the races are different?"

I shall post Don's photos once I have his permission to.

Mike Turnbull

Author: yyattung Time: 5/05/2008 21:56

多謝大家!!

跟貼!!

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Author: Tony Time: 5/05/2008 22:06

我以為你喪叫無影添~~

Author: fsp Time: 6/05/2008 00:01

跟尾

ops:

4 May 2008

Southern Waters of Hong Kong 香港南區水域

A wonderful trip! Thanks all the experts!

Author: cywong Time: 8/05/2008 22:58

The identification of this juvenile tropicbird is interesting, so I tried to ask the opinion of Dr. Nic Dunlop because he is familiar with both Red-tailed and White-tailed Tropicbirds. Dr. Dunlop is an animal ecologist with a long term research interest in tropical seabirds and had conducted research on Tropicbirds.
His reply is : The juvenile White-tailed Tropicbird has a continuous black area on the outer primaries (seen also in the adults). This is just a few light grey bars in the Red-tailed.

Here are 2 photos of Red-tailed Tropicbirds on nests taken by Dr. Dunlop

Author: tmichael Time: 9/05/2008 22:42

This point about the fore-webbing of the outermost primary always being black in White-tailed but never in Red-tailed is the main reason we believe our bird to have been White-tailed - the flight photos obtained have helped immensely.

Dr Dunlop's input is nevertheless gratefully received corroboration.

To my mind our bird still has a bigger bill than the birds in Dr Dunlop's photos.

I wonder therefore how useful impressions of bill size actually are.

Mike Turnbull

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