Sunday, 22 December 2013

Lower Cuckmere 22 December 2013

Sunday 22 December.  Visited the Cuckmere with John King to look at gulls again.  We spent over three hours with a flock of about 500 north of the Golden Galleon with an adult Caspian Gull showing well but distantly for about half that time.  Also 4, possibly 6, adult Yellow-legged Gulls, two adult argentatus Herring Gulls and several frustratingly brief views of a putative first-winter Caspian Gull.  The gulls eventually all flew south and we then walked down to the scrape on the east side of the river seeing Bar-headed Goose, Kingfisher and roosting Spoonbill.  There were about 2000 gulls in the fields west of the river but rather distant from where we were.  

Caspian Gull looking left showing long pale bill, white head, small eye, darker (than Herring Gull) mantle and white tongue to p10 visible on this image
second from the back showing smaller head, annaconda nexk, washed out bill and longer thinner legs
my best image of the head side on, or would be if not somewhat obstructed by something flapping in front of the lens

very long winged even when out of focus

this image best captures the birds distinctive look
stilt like legs, pale bill and small dark eye showing well in this image
[February 2014 addition:  John King and I were completely happy that this bird was an adult Caspian Gull for the reasons set out in the above captions (long, thin washed out bill, small unstreaked pear shaped head, small dark eye, reddish eye-ring, darker than argenteus mantle, annaconda neck, dull long thin legs, hanging rear belly and pattern of p10). We felt that it was a classic bird in every respect, a view shared by several others that I have spoken to (some, like me, quite cynical!) who have seen these images posted on my blog. Unfortunately it never stretched its nearer wing for me to photograph so I couldn’t be sure of the pattern on p4 or p5. Without seeing these features I felt that attempting a trait score might be pointless but without seeing enough for an absolutely certain trait score I feel it is conclusive enough to support its identification as a pure Caspian Gull. The following comes from British Birds104:702-742, Identification of Caspian Gulls part 2 (December 2011) and applies to adults:
P10 overall pattern: white to black ratio. Less black than white. Score 0 (applies to all sampled Caspian Gulls, 25% of hybrids and 39% of Herring Gulls).

P10: white tip. Complete sub-terminal bar. Score 3 (applies to 12% of Caspian Gulls, 25% of hybrids and 7% of Herring Gulls). This is highest scoring (worst) trait noted on this bird, although a similar bird is shown on Steve Arlow’s blog (see above for details) as being ‘typical of some Caspians but generally not commonly seen on the birds in south Essex’.

P10: tongue. White or whitish. Score 0 (applies to 76% of Caspian Gulls, 17% of hybrids and 2% of Herrings).

P5: extent of black. Not seen. Score 0-4. Note that only 1% of Caspian and 0% of hybrids scored 4 for this trait so that outcome can safely be excluded while only 9% of Caspian and 25% of hybrids scored 3 making that a very unlikely outcome too. Most likely score 1 or 2.

P4: extent of black. Not seen. Score 0-2. Most likely score 2 as per 72% of Caspian and 83% of hybrids.

Iris peppering. Dark-looking. Score 0 (applies to 47% of Caspian Gulls but none of the sampled hybrids or Herring Gulls).

Eye-ring colour. Dark/deep orange to red. Score 0 (as 21% of Caspians, 57% of hybrids and 6% of Herrings).

Bill shape. Slim, slight gonydeal angle (ratio 2.4-2.79). Score 1 (applies to 87% of Caspian Gulls, 42% of hybrids and 8% of Herring Gulls).

Leg length. Long. Score 0 (applies to 52% of Caspian Gulls, 42% of hybrids and 5% of Herring Gulls).
The total score for this bird is in the range 4-9 depending on the unseen extent of black on p5 (0-3) and p4 (0-2) but almost certainly 7-8. This is comfortably within the range of the known pure adult Caspian Gulls sampled (4-12) and just outside the range for hybrids (9-20). Adult Herring Gulls ranged from 12-20. This supports the identification as a pure Caspian Gull made on the observed features, none of which suggest any hybrid influence at all. ]


dark mantle, large size, bright pink legs and extensive white primary tip all point towards argentatus Herring Gull, but although the head was streaked it wasn't excessively so
colour-ringed Lesser Black-backed Gull xx54
Yellow-legged Gull in the Cuckmere
red eye-ring just about visible on this one
sleeping Spoonbill
Saturday 21 December.  Nice views of 4 Purple Sandpipers at Shoreham Fort despite/because of the atrocious weather.  I sheltered behind the yellow fishermen's container. nothing was seen out to sea but visibility was poor as well as having strong winds and driving rain to contend with.

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