查看完整版本: Big Gull ID again, please

Big Gull ID again, please

Q.1
[img]http://us.f6.yahoofs.com/hkblog/0CQiNN2ZHxI__DOT__HSgbnAU-_1/blog/20100129041536219.jpg?ib_____D7aRoRBsK[/img]

[img]http://us.f6.yahoofs.com/hkblog/0CQiNN2ZHxI__DOT__HSgbnAU-_1/blog/20100125070211914.jpg?ib_____DjvZ1VNKJ[/img]

I would like to ask for expert advice on the identity of the two adult gulls left of the adult Heuglin's Gull. My bet for the two big gulls on the left is Vega-type Gulls: I overheard some fellow birders talking about taxon "birulai", so I'll make it the null hypothesis here ^^. Indeed these two birds are smaller, not bigger than the Heuglin's; the legs are pink as portrayed and seen in the field, as compared to the yellow legs of Heuglin's; the neck streaking is comparatively rich; also the mantle colour is paler, but not much paler than the Heuglin's beside them.

Q.2
[img]http://us.f6.yahoofs.com/hkblog/0CQiNN2ZHxI__DOT__HSgbnAU-_1/blog/20100125070234411.jpg?ib_____D5qz1lM.9[/img]

Second question please: what are the two adult gulls on the right? I would guess Heuglin-? hybrids, because the mantle colour is paler than normal Heuglin's, leg is yellow for one and orange-pink for the other. Also, should the black spot on the bill be interpreted as a mark for 3rd year gulls?

Maipo Boardwalk
23/1/10

Thanks for replies in advance!

[[i] Last edited by kkoel at 29/01/2010 16:19 [/i]]

The ID on photo is best when compared with a standard Heuglin Gull on the same photo, else the degree of pale would be very difficult to assess.  I think a lot of present ID is based on the degree on pale on the mantle, which is somewhat variable on Heuglin (depending also on summer and winter plumage as illustrated on a Japanese book).  The other major factor is the degree of neck streaking, which is changing in the course of the winter.  Light colour of adult seem to be relative stable and so it is relatively useful feature.  Last, the pattern on the wing is useful, and so should be given more attention than in the past.

Overall, I think Koel's analysis are sound, although I am inclined to have 1 Yellow-legged on the second set of photo (the bird on the right).

HF Cheung

Thanks Fai Gor for your reply! 3551smile445

[u]Photos 1&2[/u]

As Koel says, the two birds on the left are closer to vegae than heuglini, much closer. The progression of moult (p9 nearly complete, p10 growing) is better for vegae, though probably within range of the most advanced heuglini. The pattern of p10 is more typical of vegae than heuglini, as is the presence of a small white spot on p9 (though neither of these are definitive).

The left hand of the two in Photo 2 (right hand bird in photo 1) shows very extensive streaking extending right over the chest, which fits vegae much better than heuglini. The other of these birds also appears to have fairly extensive streaking. Obviously, the legs of the one bird are obviously pinkish, while those of the right hand bird slightly less so.

In terms of mantle colour, one has to be slightly careful as the birds are standing at different angles. However, they do genuinely appear to be paler.

[u]Photo 3[/u]

Could the right-hand most bird not be the left hand adult in Photo 1? Moult appears the same, with p9 nearly complete. The second of these two does look more like a bird showing features of both heuglini and vegae. As for the bill pattern, it might indicate immaturity, but may be just be individual variation. The bird preening its tail is immature though, as it has dark in the tail (perhaps you meant this bird??).

Certainly neither appears to be mongolicus due to one or more of the amount of head streaking extent and intensity, moult and leg colour.

Incidentally, this issue of hybrids is why vegae is not on the HK List. However, I think we've reached the stage now where we can be confident this species is occurring in a non-hybrid form. I'm in the process of preparing something regarding this issue for circulation around the Records Committee.

Geoff

[[i] Last edited by cgeoff at 28/01/2010 14:36 [/i]]

Hi Geoff,

Thank you for your detailed reply!

For photo 2, I was only referring to the 2 pale-mantled adults on the right (for I'm not confident with the immatures - which I guess are all Heuglin's...) - and I'm sure these two individuals are distinct from the two vegae-type gulls in photo 1 - hope it helps further analysis.

Can I also ask for photo 2, is it possible to interpret the moult pattern of the resting adult gulls with folded wings?

Koel,

My reply had a couple of problems, which probably confused, and I've now edited it. Pls see above.

Geoff

Koel,

Thanks for posting your photos and adding to the large gull debate.

Agree with Geoff on ID but would go further in favour of Vega Gull for most of your birds. If seen in Japan or North China, I dont think there would be much doubt about both birds in Photo 1, the left bird in Photo 2 and the right bird in Photo 3. Structure, size, mantle colour, head streaking, wing tip patterns all look good for Vega. Wing moult can often help but as Geoff says at this time of year, birds still finishing moult of outer primaries can either be late Vega or typical Heuglins so it doesnt help much in trying to spot hybrid traits.

The only obvious other difference from Vega is leg colour with the left bird in Photo 3 having yellow/peachy legs which are indicators of hybrid origin, but where to draw the line? That is the great debate. Some authorities consider both taimyrensis and birulai to be not good taxa and merely hybrids. To my eyes, taimyrensis is fairly consistent as a paler and larger version of nominate heuglini [but from the field bird-watcher's point of view still appears to be a form of Heuglins Gull, both in juvenile and adult plumages as well as orange/yellow leg colour etc. Lesser-blacked Gull is similar in Europe with the larger paler race graellsii being dominent in the west where it mixes widely with Herring Gulls compared to the smaller much darker nominate fuscus in the east - the reverse of heuglini/vegae.

Birulai was named as a paler version of Vega in the north-west of Vega's range, but this taxon is more difficult to describe and there appears to be a range of different hybrid variations with differences in leg and mantle colour, probably arising from its contact with taimyrensis. The right hand bird in Photo 3 appears to be one of these intermediates. Note that small numbers of similar gulls with yellow/peachy legs [only a few percent] also occur much further east in Japan with wintering Vega Gulls.

Lastly, your comment about the black on the bill does not appear to be a sign of immaturity in your birds as the primaries appear to be fully adult. There is a good paper on variability within Vega Gulls in Surfbirds by Chris Gibbons in which he counted 28% of wintering adult Vega Gulls had black [as well as red] on their lower mandible, with less than 10% with black on both mandibles.

Mike Chalmers

Wow...all the comments above are very detailed, specific and advanced!  I did learn much from it.  Thanks all a lot! 3551875328cc445

Thanks Mike for the detailed comments - next time I'll know better where to look on the gull for ID!

I guess more detailed observation of these big gull taxa in Hong Kong can really help clarify the distribution of the Mongolian / Vega / Heuglin's complex in East Asia, and hence their taxonomic relationships. Given the propensity for juvenile gulls to wander, maybe if we look closely at the young big gulls, we'll find more Vega than we might have noticed! =)

More pics on a possible Vega-Heuglin's hybrid from the same day, the left bird in photo 1 below and the same bird in photo 2.

[img]http://us.f6.yahoofs.com/hkblog/0CQiNN2ZHxI__DOT__HSgbnAU-_1/blog/20100129042019785.jpg?TTAgMZLBNorZvxpb[/img]

[img]http://us.f6.yahoofs.com/hkblog/0CQiNN2ZHxI__DOT__HSgbnAU-_1/blog/20100129042030696.jpg?TTAgMZLBH0XyPbF7[/img]

[[i] Last edited by kkoel at 29/01/2010 16:22 [/i]]

Koel,

I would say your gull is [i]taimyrensis[/i] with unusually strong head and neck streaking. Its [i]taimyrensis[/i] based on the mid-grey mantle colour, yellow legs and active wing moult on outer primaries. Whilst the head and neck streaking is a much better fit for [i]vegae[/i], other features are all in favour of [i]taimyrensis[/i]. We just have to accept that not all these gulls will fit the standard pattern and a range of features are to be expected given their origins from intergrading between different forms. The striking pale yellow iris is also within the range for [i]taimyrensis[/i] and the heavy bill indicates it is probably a male.

Of interest is the darker-mantled bird on the right of your Photo 1. Given the contrast with the [i]taimyrensis[/i] on the left and given its lighter sleeker appearance and build, I would consider it to be a good example of nominate [i]heuglini[/i], whose status in Hong Kong needs more work but is probably very scarce.

Mike Chalmers

Mike,

Thanks for your reply. It's very interesting to see the range of plumage / structure differences seen in taimyrensis - which actually is understandable if we regard taimyrensis as an intergrade between nominate vegae and heuglini. For the dark-mantled gull on the right of photo 1, I have always been under the impression that it was one of the 'taimyrensis'-type too - as the mantle colour is rather lighter than that of Lesser Black-backed Gull taxon graellesi, whereas for heuglini I've seen some photos from the christopher helm Gull guide portraying a mantle shade darker than graellesi. I guess your revelation will make me reconsider many of my previous 'taimyrensis' as 'heuglini'!

Koel