Saturday 4 January 2014

taimyrensis - juvenile & 1stw

Juvenile, 1CY

Juvenile and first winter taimyrensis are distinctive gulls. Juvenile plumage is superficially closer to smithsonianus than anything else though the rump and uppertail coverts and the vent and undertail coverts are much less heavily marked. Within Kansai smithsonianus isn't likely to present any problems and Vega Gull is the taxon in most need of elimination.


It averages smaller than Vega but there's a lot of overlap, not least because Vega is so variable. It's  longer-winged in flight and more attenuated at rest. In general taimyrensis is a more uniform, browner gull. In brief the more obvious plumage differences from Vega are:-
Saddle dark centred feathers with fairly even pale fringes rather than strongly patterned type.
Tertials mainly dark with usually narrow fringes on the distal half, sometimes with slightly lighter enclosed sub-terminal area. Vega with more complete fringes and stronger patterning.
Greater coverts with obvious brown bar which may be restricted to the bases of the outer half or more rarely throughout the full length. The innermost are also dark centred with narrow pale fringes much like the tertials. Vega is effectively chequered throughout.
Rump and uppertail coverts are rather white contrasting with the tail. The edge of the rump and longest uppertail coverts have a large dark arrowhead creating a horseshoe of prominent spots but with light markings across the rump. Vega usually more evenly and heavily barred across the rump recalling smithsonianus.
Vent and undertail coverts basically mirror the upperparts with a ring of promintent spots but clean centre. Again Vega is more barred, especially on the central undertail coverts.

When I start gulling at the beginning of November taimyrensis is already present, so I'm uncertain of their arrival dates. They're quite numerous throughout the month, sometimes in discrete flocks of up to 30 and can make up 50% of the large gull population at that time. Numbers drop off in December and by mid-month there might be no more than 10 present. Birds are in full juvenile plumage when they arrive and by the time the last birds are leaving they will often have replaced the mantle a sometimes a small number of scapulars.

Fig 1 (as Figs 2&3)   Dark scapulars, innermost greater coverts and tertials create uniform brown upperparts. 21 November 2010. 

Fig 2 (as Figs 1&3)   The rather uniform brown patch surrounding the eye on an otherwise more lightly marked head is typical.

Fig 3 (as Figs 1-2)   Sparsely marked undertail coverts compared to Vega, though this bird is more heavily marked than many.

Fig 4 (as Fig 5)   Profile shot showing rather attenuated structure compared to Vega and a typical coverts bar. 13 November 2011.

Fig 5 (as Fig 4)   Here showing the largely white rear end with prominent bordering spots on sides of rump and vent.

Fig 6 (as Figs 7&8)  Another good example, the centres of the tertials are often lighter brown sub-terminally as on this individual. The coverts bar is less prominent than on most birds. 3 November 2009.

Fig 7 (as Figs 6&8) Note how weakly the centre of the rump and uppertail coverts is compared to the bold bordering horseshoe of arrowheads.

Fig 8 (as Figs 6&7)   Note directly behind is a Vega with whiter wing coverts, and already second generation saddle and pale based bill. To the rear left is another taimyrensis with a more conspicuous coverts bar. 

All the birds above are typical juveniles and perhaps show a surprising degree of consistency given how variable the adults tend to be. Below are four shots of a bird which does differ from the norm, though it's a matter of colour saturation. The scapulars are darker brown and the terials blackish-brown. All these feathers have very narrow even fringes. The coverts bar is very dark because of a lack of contrast with the gound colour. The rump is more heavily marked than normal.

Figs 9-12   Present from  5 November to 10 December 2010.

Below is strikingly different, the only example I've seen of a grey bird and perhaps it is more at the heuglini end of the spectrum.

Fig 13   The markings are basically the same as other birds but it has a strikingly clean appearance with more piano key greater coverts. 23 November 2010.

Fig 14   A normal brown taimyrensis on the right and this grey bird on the left.

Fig 15   Crisply marked axilliaries and distinctly spotted flanks. Flanks usually don't look as spotted until spring when the brownish ground colour has faded leaving the darker spots isolated. 

Fig 16   The wings look blacker than normal.

In December birds begin moult to first winter by replacing mantle feathers and sometimes a limited number of scapulars.

Fig 17   Mantle replaced by second generation feathers is normal at this time. 12 December 2010.

Fig 18   An bird with more white in the tertials and much more strongly patterned scapulars than usual. The bill is much paler than expected and the underparts also appear to be in moult. It nevertheless has a bold coverts bar and dull primary window putting it comfortably into the taimyrensis range. Or hybrid?

First winter 2CY

Birds start to return from about mid-March and the juveniles have transformed into very different but equally distinctive gulls. The saddle has been replaced and moult seems to be ongoing as the most recently replaced feathers, some upper tertials and rear scapulars, inner greater coverts and central median coverts are similar in appearance but darker, not yet as faded as the saddle.

The following images are members of a flock I first saw on 20 March 2012 which was still present  until at least 1 April, my final gulling trip that winter.

Fig 19   Three first winter birds compared to a faded first winter Vega on the right. Two adults (facing away) are long-winged compared to Vega and even at this angle have more prominent red gonys spots. 20 March 2012.

Figs 20-21   A large presumed male, still with completely dark bill unlike the other first winters.

Figs 22-24   The same male (Figs 20-21) in flight.

Fig 25   Most birds are mainly white-headed by this time with a distinct collar of spots and still have dark, finely marked underwings. 

Fig 26   Though big males look bulky, most birds are long and elegant.

Figs 27-29   More recently moulted, hence darker upper tertials, rear scapulars, innermost greater coverts and central median coverts. First winter Mongolian Gull in the foreground of the lower two images.

Figs 30-31   Wings long and dark compared to Vega, white rump contrasts markedly with the tail.

Figs 32-33   These images are include to illustrate two very different but typical head shapes, the long sloped forehead, huge bill and forward placed eye and the following shot of the same bird seconds later with a steeper forehead, flatter crown and shorter-looking bill. 3 April 2011.

Finally six digiscoped shots of a distant and very aggressive bird that stayed out at the river mouth. Initially I thought it might be a Caspian based on structure but once I saw the plumage details I realised that wasn't possible. Nevertheless, it's interesting that could be the first thought and again is more suggestive of heuglini.

Fig 34   The impression at long distance is of a long-bodied and long-necked Gull which has no affinity whatsoever with Vega.

Figs 35-39   21 March 2010

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