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Subject: [Shearwaters] unknown Shearwaters [Print This Page]

Author: 深藍-Owen Time: 25/04/2009 17:47 Subject: unknown Shearwaters

HK South water
Apr 25, 2009

Please help id . Thanks.

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Author: kmatthew Time: 25/04/2009 18:10

I looked something up between Short-tailed & Sooty, and I came up with these info which may help identify this shearwater.

Sooty Shearwaters have a longer, stout bills. The darker chin is not contrasty with rest of the lower body. Primaries reach only to tail when sitting still. The white underwing is most prominent on the median primary coverts. The white median primary coverts & median secondary coverts contrast strongly with the dark flight feathers. The wings & tail appear longer when compared with Short-tailed.

Though there are many variations in plumage within Short-tailed Shearwaters, Short-tailed have a much paler tone to it's body in general, with a near all pale underwing. Including pale primaries. It will also have a paler throat and breast when compared with Sooty. Tail and wings appear shorter then Sooty Shearwater.

All the features of this bird suggest a Sooty Shearwater to me. The dark body and dark flight feathers are very clearly shown in the photos. The tail also look long to me in the photos.

I am not entirely sure

...But experts advice will be better than my observation from second hand information...

[ Last edited by kmatthew at 25/04/2009 18:13 ]

Author: 深藍-Owen Time: 25/04/2009 21:19

Thanks Matthew, actaully some people on the boat also think its a Sooty.

Owen

Author: tmichael Time: 25/04/2009 22:19

Separation of Sooty and Short-tailed Shearwaters, especially lone birds out of their regular range is notoriously difficult. A couple of useful on-line references seem to be:

www.aba.org/birding/v40n2p34.pdf

and

http://thebirdguide.com/pelagics/book/id_sosh_stsh.htm

I've taken the liberty of doing what the author of the latter paper does and have heightened the contrast on Owen's photo just to highlight the distribution of the whiter areas on the underwing of the bird we saw today:

Although the existence of birds like the rightmost of the two birds in the photo of two Short-taileds together in the first paper above seems to make reliance on underwing pattern unsafe I must say I think our bird looks extremely good for Sooty. Compare it for instance with the bird shown on this page:

www.kiwifoto.com/blog/2008/10/13/monterey-bay/ (you need to scroll down a little)

I think it looks identical.

I have seen a lot of Short-tailed Shearwaters from boats in HK over the last three years, and have been acquainted with Sooty for over 35 years, from UK and elsewhere, including thousands in California last summer, and while I don't claim to be able to separate them (for purposes of comparison I was desperate to find a Short-tailed amongst the Sooties in California but couldn't) I was really struck by how unlike Short-tailed the jizz and flight of this bird was - to me, unlike Short-tailed, which always seems to me a relatively chunky bodied compact shearwater, this one seemed like a large shearwater, and had a rather more relaxed flight style on what seemed to me like longer wings than Short-tailed.

It'd be great if there were some more photos, of any quality, and if those who took them could post them here.

Mike Turnbull.

[ Last edited by tmichael at 25/04/2009 22:24 ]

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Author: cmichaell Time: 27/04/2009 23:53

SHORT-TAILED/SOOTY SHEARWATER

Congratulations to those who spotted this bird and appreciated its potential to be a Sooty Shearwater. Was hoping that some additional photos might be posted to help with id of this interesting bird. On the two we have, I think its going to have to remain one of those mysteries.

There are pluses and minuses. The one photo of the underwing is certainly interesting. Short-tailed is very variable and the pattern could fit either species on first impression. However, to my eye, the white on the inner underwing is a bit too wide for Sooty, where the white is usually limited to the median coverts in the middle of the wing and does not typically extend so far back towards the trailing edge. This results in the most prominent and widest area of paleness on the underwing of Sooties being on the primary coverts on the outer wing rather than sharing prominence with the inner wing like the photo suggests.

Other comparisons are structural. Sooty has a longer and less slender bill than Short-tailed, and this is accentuated by a more sloping forehead. This is hard to judge in the photos as the bill is not shown side-on but again it appears to be closer to Short-tailed and not as long as expected for Sooty. Also in the lower photo, the tail end appears "lumpy" suggesting that feet may be projecting beyond the tail. This point is in favour of Short-tailed but not Sooty. Lastly to my eye, the wings are not quite as long in proportion to the body as I would expect for a Sooty, but OK for Short-tailed.

However, many of these points are subtle and a wider series of photos backed by field descriptions of flight style and other observations would help with a decision one way or the other.

Lastly, it is worth noting that there are estimated to be over 20 million Short-tailed Shearwaters and they are known to pass up the East Pacific in our spring in big numbers after leaving their Australian breeding grounds, whereas the numbers of Sooty Shearwaters are an order of magnitude less at several million and their numbers are split between New Zealand and Chile. Furthermore, NZ birds appear to take a more northerly route not close to East Asia and as a consequence complete their clockwise circuit of the Pacific more to the east. This results in them being much more numerous on the west coast of USA on their return journey than Short-tailed. For any betting man, the odds on Sooty in the South China Sea are thus much longer.

Mike Chalmers

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