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Another Large Gull SP., Tainan County, Taiwan: taimyrensis or mongolicus? (1 Viewer)

S

SteveMM

Well-known member
Apologies if this is getting boring! This is the last one that's bothering me (for now at least).

I'm pretty sure this bird is just a very 'frosted-looking' first-winter taimyrensis due to fairly small (but still worryingly obvious) predominantly brownish-looking window on the inner primaries, dark outer greater coverts, well-patterned scapulars (with brown markings), and (perhaps most importantly) lack of obvious signs of wear throughout the upperwing coverts.

However, it does have one or two pro-mongolicus features, such as very white head and body, very white fringes to the upperwing coverts, subtly silvery-centred scapulars, and a narrow tail band.

I think Mongolian should look very bleached and worn through the wing by now, which is the main reason I do not prefer it. (Photo taken Feb 9 BTW.)

Confirmation or otherwise would once again be greatly appreciated!

Steve
 

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SteveMM said:
Apologies if this is getting boring! This is the last one that's bothering me (for now at least).

I'm pretty sure this bird is just a very 'frosted-looking' first-winter taimyrensis due to fairly small (but still worryingly obvious) predominantly brownish-looking window on the inner primaries, dark outer greater coverts, well-patterned scapulars (with brown markings), and (perhaps most importantly) lack of obvious signs of wear throughout the upperwing coverts.

However, it does have one or two pro-mongolicus features, such as very white head and body, very white fringes to the upperwing coverts, subtly silvery-centred scapulars, and a narrow tail band.

I think Mongolian should look very bleached and worn through the wing by now, which is the main reason I do not prefer it. (Photo taken Feb 9 BTW.)

Confirmation or otherwise would once again be greatly appreciated!

Steve
Click to expand...

I seem to be in the horrible habit these days of asking first and reading second (when it would be better to do things the other way round).

It looks to me like the inner 3-4 greater coverts on this bird have been replaced. This would put the bird in active moult in February and therefore make it a northern breeder, and by extension rule out mongolicus completely, right? Or have I got this all horribly wrong?

Again, all comments welcome!

Steve
 
No need to apologise Steve! Nice ones these Taiwan Gulls!

This has to be a 'taimyrensis' type, with those dark greater coverts, terial pattern, structure and pale underwing, pale underwing, which btw mongolicus also shows, along with paler greater coverts and paler again inner primaries. Athought tail pattern could fit mongolicus it would still have a much paler plumage at the given time. Here are some Oct mongolicus:http://gulls.tistory.com/category/SPECIES/한국재갈매기(Mongolian Gull)
and some early March 'taimyrensis' types by Peter Adriaens:http://www.pbase.com/smiths_1/taimyr_gull
and here:http://tori3.sakura.ne.jp/birdworld_menu/kamome/nisisegurokamome/taimirusegurokamome-1w.htm

JanJ
 
JANJ said:
No need to apologise Steve! Nice ones these Taiwan Gulls!

This has to be a 'taimyrensis' type, with those dark greater coverts, terial pattern, structure and pale underwing, pale underwing, which btw mongolicus also shows, along with paler greater coverts and paler again inner primaries. Athought tail pattern could fit mongolicus it would still have a much paler plumage at the given time. Here are some Oct mongolicus:http://gulls.tistory.com/category/SPECIES/한국재갈매기(Mongolian Gull)
and some early March 'taimyrensis' types by Peter Adriaens:http://www.pbase.com/smiths_1/taimyr_gull
and here:http://tori3.sakura.ne.jp/birdworld_menu/kamome/nisisegurokamome/taimirusegurokamome-1w.htm

JanJ
Click to expand...

Thanks again for all these links, Jan, they help enormously.

It's the wide range of variation possible in the taimyrensis here that causes me all the confusion, with some surprisingly white individuals. It looks like wear is the most useful way of picking out mongolicus at this time of year, as it was with the only real definite I have found in this recent period of looking (first bird attached, on the left with another taimyrensis).

Out of interest, I also have the second bird attached aged as a first-winter taimyrensis. Malling Olsen and Larsson states that some taimyrensis replace juvenile coverts with adult-type grey feathers, which is what seems to be happening here. Or have I got the age wrong?
 

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One thing though:
the bird in post #1 has not moulted any greater coverts.
The inner ones are just as juvenile as the rest, just with different pattern.
 
smiths said:
One thing though:
the bird in post #1 has not moulted any greater coverts.
The inner ones are just as juvenile as the rest, just with different pattern.
Click to expand...

Thanks for the correction, Smiths.

The only reference I have for these things in Malling Olsen and Larsson, which deals with taimyrensis under heuglini. It states juvenile moult to first-winter partial (Nov-Mar) (in heuglini), including some greater coverts (all greater coverts in most advanced birds). I took the dark greater covert bar ending abruptly (whilst still rather broad) to indicate a moult limit. My bad!
 
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