Semi-retrospective Sandpiper

By Keith Vinicombe

On the morning of Thursday 10 November, I discovered a greyish stint feeding with a Dunlin at the mouth of Hollow Brook, in the north-eastern corner of Chew Valley Lake, Somerset. I simply couldn’t get close to it, but it appeared to have a solidly dark crown, with no split supercilium, and a fan-shaped patch behind the eye. It also lacked any trace of a white mantle V, seemed to show a short primary projection and appeared to have a black shaft line on the feathers of the upper row of lower scapulars, expanding into a black blob towards the feather tips. All these features suggested a juvenile Semipalmated Sandpiper.

Semipalmated Sandpiper (smallest shorebird in centre of image, just right of the much-twitched Sharp-tailed Sandpiper, Chew Valley Lake, Somerset, 19 November 2011). The bird's unsplit supercilium is just visible on this photo. By Richard Andrews.

However, it was just too far away to convince me. I went back the following day and watched it for several hours, but I still couldn’t get any closer. I returned again on 15 November, this time armed with an old 60x zoom lens, which I managed to lose in the middle of a reedbed! I spent half the morning trying to find the bloody thing, which, amazingly, I did. Unfortunately, the views were no better, but I did secure 54 rather poor digiscoped images, none of which was sufficiently detailed to provide the proof that I was looking for. Reluctantly, I came to the final conclusion that I had to let it go.

On the weekend of 19 and 20 November, the stint relocated to Herriott’s Bridge at the southern end of the lake, but it was still distant (300 m). The problem now was that everybody was completely distracted by the presence of a juvenile Sharp-tailed Sandpiper that was in the same flock! I decided to try for better views once the crowds died down, but unfortunately, it left overnight on 20th.

Semipalmated Sandpiper (centre bird, Chew Valley Lake, Somerset, 19 November 2011). Note the dark crown and small fan-shaped patch behind the eye, both just visible on this digiscoped image. By Richard Andrews.

It seemed doomed to remain ‘the one that got away’, but about a week later, I had a light bulb moment. On 19 November, Richard Andrews had photographed the Sharp-tailed Sand from a ringing ride near Herriott’s Bridge. I phoned him and asked if, by any chance, he had the stint in any of his photos. To my amazement, he did, and promptly sent me 14 quite reasonable shots of it. As I opened his email, there right before my eyes, was the confirmation that I had been looking for: it was indeed a juvenile Semi-p, just beginning its moult into first-winter plumage!

Needless to say, I felt both elated and vindicated, but I also felt a little uneasy about claiming a bird retrospectively from a series of digital images. Call me old fashioned, but I prefer to identify my birds in the field. Thinking it over, I decided on a belt and braces approach: I sent the photos to Killian Mullarney, who very kindly and very promptly replied with a strong endorsement of the ID as a Semi-p.

This was the lake’s 10th BB rarity and the 16th American bird of a truly remarkable autumn. Even the ‘Good Old Days’ weren’t that good!

Wilson's Snipe

Now split from Common Snipe Gallinago gallinago, Wilson's Snipe G delicata is the lookalike Nearctic counterpart. For decades distinctions between the two have been murky, with much variation and similarity clouding the picture, but in recent years the ID criteria have become clearer and Wilson's - although still bestowed with mega rarity status - is being identified with increasing confidence and regularity in Britain. It surely remains under-recorded here, however, given that 115 have now been recorded in the Azores (for full details see the Birding Azores website).

A major photo ID guide in the January 2012 issue of Birdwatch looks at this problem, with extensive photos of both Common and Wilson's Snipe and discussion of the ID criteria for the rarer species. These videos, shared from YouTube with due credit to those who shot the footage, supplement the still images in the magazine.

 The above clip has interesting 'song' on the soundtrack.

Wilson's Snipe: accepted British records

• 1998: Lower Moors, St Mary’s, 9 October 1998-7 April 1999 (British Birds 101: 539-540).
• 2007: Lower Moors, St Mary’s, a first-winter on 3 October, with the presumed same bird from 1 October to 22 April (British Birds 103: 587); also three juveniles moulting to first-winter plumage at the same site, 21 October-26 December (British Birds 104: 582).
• 2008: Wingletang, St Agnes, 11 October (British Birds 104: 582).

In addition, it seems highly likely that the autumn 2011 bird, present at Lower Moors from September into November and documented so thoroughly with photographs, will become the seventh accepted record in due course.

References and further reading 

Bland, B. 1998. The Wilson’s Snipe on the Isles of Scilly. Birding World 11: 382-385.
Bland, B. 1999. The Wilson’s Snipe on Scilly revisited. Birding World 12: 56-61.
Reid, M. 2008. Identification of Wilson’s and Common Snipe. British Birds 101: 189-200.
Rowlands, A, Small, B J, and Bradshaw, C. 2009. From the Rarities Committee’s files: Identification of Wilson’s Snipe and assessment of the first British record. British Birds 102: 425-434.

Continental Greylag Geese

Three of the continental Greylags at Chew Valley Lake.

By Keith Vinicombe

As many people will be aware from the various bird information services, recent weeks have seen a major displacement of Tundra Bean Geese into Britain, as well as flocks of White-fronted Geese occurring in areas where they are not usually seen. However, a third species of goose, Greylag, seems to have fallen below the radar, despite unusual records at a number of places, such as Portland Bill in Dorset.

Being a common feral species, it would be easy to assume that these records lack significance. However, on 17 November, I came across a party of five at Blagdon Lake in Somerset, an unusual record there for the time of year. When I looked at them through the scope, there was something distinctly odd about them, although I couldn’t put my finger on what it was. However, they seemed very fresh and immaculate and both their upperparts and flanks were very heavily barred with white.

A couple of hours later, I was at nearby Chew Valley Lake when, at about 13.30, I heard some Greylags calling. A flock of nine appeared high over the lake and dropped in just to the north of the hide. Their behaviour was strongly suggestive of wild birds and, like those at Blagdon, there was something ‘odd’ about them. I took a large number of digiscoped photographs, and a couple of the better ones are shown here.

Note the pink bills and subtly different bill shape.

According to BWP, there are two subspecies in Europe, nominate anser and eastern rubirostris. Anser occurs in Iceland, Scotland and coastal Norway and has a shorter, thicker and rather triangular bill, predominantly orange in colour (with just some pink behind the tip). Also, it has a pale buffy-grey head and neck and finely barred upperparts and flanks. Our feral breeding birds seem to correspond with this race. Rubirostris, however, is slightly larger and generally paler than anser, with stronger and whiter transverse barring and a longer bill that is wholly pink, apart from the white nail. Birds in central Europe are apparently intermediate.

The Chew birds were indeed heavily and contrastingly barred, they also had longish and rather thin bills, perhaps recalling the bill of Taiga Bean Goose in shape. Their bills were predominantly pink, although at least some had orange at the base. Also distinctive was that the white nail at the tip of the bill was very obvious and contrasting. From BWP, it was clear that they did not fit nominate anser, although, given the orange at the bases of their bills, they did not fit pure rubirostris either. However, they were clearly some way along the spectrum towards that subspecies.

Since then, Nigel Milbourne sent me a good photo of two of the Blagdon birds, and this shows that the left hand one did indeed have an all-pink bill (see ‘Latest news’ at www.blagdonlakebirds.com for 17 November). On re-checking my own photos, it appeared that some of the Chew birds also had all-pink bills. That being the, case, I can’t see any reason why these particular individuals should not be regarded as pure rubirostris. Whatever their exact racial assignment, the important point is that it's safe to conclude that they arrived from continental Europe and were not feral or Icelandic birds. This is the first firm evidence of wild Greylags occurring at the lakes, although the late Bernard King saw a bird at Steart, Somerset, in April 1952 that resembled rubirostris.

Apparently, there has been a big movement of Greylag Geese on the French side of the English Channel, with 200 past Jersey this month and “thousands” past various sites in Normandy. These are thought likely to be Swedish birds deflected westwards en route to Spain (www.guernseybirds.or.gg). It would seem that, like the Tundra Beans and European White-fronts, there has also been a major arrival of continental Greylag Geese - right under our noses!

Roosting Caspian Gulls

By Keith Vinicombe

On a recent trip to East Anglia, one of our target species was Caspian Gull, and a report of six at Minsmere persuaded us to pay a late afternoon visit to the RSPB’s flagship reserve.

A lot has been written about Caspian Gulls in recent years, but this has tended to polarise birders into two camps: those who fully embrace the subject and those who steer well clear of it – many people are simply put off by all the detail.

Among all the talk of black bars on P5 and white tongues on P10, one thing that tends to get overlooked is the species’ jizz. Or to put it another way: how would you notice a Caspian Gull in the first place? Our experiences at Minsmere may help to clarify this. On our arrival, a quick scan through the gulls soon revealed a strong candidate. It was sitting down, front on, with its neck hunched into its body, as shown in the digiscoped photo below.

The adult male Caspian Gull is the bird at the front sitting down. Photo by Keith Vinicombe.

It stood out from the nearby Herring Gulls due to its pure white head, its beady black eye, its long down-turned gape line and its rather long, slim, washed-out, yellowy bill. It was a large, bulky bird, with a deep and well-rounded breast, but it also had a gently rounded head and, unlike the other large gulls, a rather benign, gentle character.

Front on, the combination of its woolly white head and beady eyes reminded me of an albatross, something that has struck me on previous occasions. The colour of the upperparts varied, looking similar to the accompanying Herring Gulls when front on, but a darker, flatter shade of grey when side on, more similar to Yellow-legged Gull.


After a while it became active and its entire shape was transformed. The head appeared small and rather rounded (although, surprisingly, it could also look very square), the bill seemed long, slim and tapered (lacking a strong gonydeal angle) and the neck was very long too. One of the most distinctive things about the extended neck was that it seemed to have an extra curve, producing a prominent bulge at the front, which gave the impression of a full crop (see the photo below).

When active, the male showed the classic Caspian gull shape, with its small rounded head, beady black eye and long, slim, tapered, washed-out bill. Note the prominent bulge in its long neck, resembling a full crop. Photo by Keith Vinicombe.

Its facial expression was completely different from the Herring Gulls, with its black eye and a narrow white upper eyering – a combination that imparted a soft, almost dopey look. The bill was a washed-out, dull yellow with small black marks behind the red spot. When walking around, the legs looked long and spindly, and they were a rather insipid greyish-pink.


After a while, a second bird glided in and sat down next to it. It was pretty much identical, except that it was distinctly smaller in every respect. The birds seemed comfortable in each other’s company and it was clear that they were a male and a female, perhaps even an established pair.


Much of the excellent work on Caspian Gulls has been carried out on rubbish tips, where the birds may be very active in their search for food. Consequently, what tends to be emphasised in the literature is their long, slim, tapered bill, the small pear-shaped head and the long, thin neck. However, their structure often looks quite different at nocturnal roosts, where the birds are relaxed and ‘ready for bed’. Instead, the head looks woolly and rather rounded and they appear short necked when the head is sunk into the shoulders. Also, because the relaxed feathers makes the head look larger, the bill does not stand out as being that different from other large gulls, in either its length or its structure.

For birders searching for Caspian Gulls in evening roosts, this relaxed, rounded pose is the normal default posture. At Minsmere, this was particularly true of the female, which often looked surprisingly Herring Gull-like in its structure and overall appearance, as shown below. In fact, at rest, the female reminded me of a giant Common Gull, with that same gentle expression, a high, rounded crown and a full, rounded breast. Also, it was not as long billed as the male.

The female Caspian Gull (middle, next to a Lesser Black-back) was distinctly smaller than the male and, as this photo shows, could like rather Herring Gull-like. Photo by Keith Vinicombe.

When relaxed, the female had a rounded body (with a full breast) and a very rounded head. The bill was shorter than the male's and did not look particularly long. Photo by Keith Vinicombe.

This is the same female, side on. In this photo, you can make out the darker grey upperparts, the dark eye and the slim, tapered bill. It also shows the flat crown and low forehaead, which are more typical of active Caspian Gulls. Photo by Keith Vinicombe.

Having soaked up the birds’ characters, we did, of course, look at the important primary pattern. Adult Caspian Gulls have much less black in the open wing than both Herring and Yellow-legged Gulls, with the black is, to all intents and purposes, confined to the rim.

At rest, the important feature to look for is the pattern of the underside of the outer primary, which is readily visible on the ‘opposite’ underwing, especially when the bird is preening its primaries. Caspian Gulls have a large white mirror at their wing-tip but there is also a long lobe of white on the inner web of the outer primary and this is separated from the white mirror by a relatively short area of black. This white-black-white pattern is very distinctive.

Three final points are worthy of clarification:
• Although the above account emphasises the black eye, when carefully scrutinised in good light, both these Caspian Gulls showed pale eyes, albeit a dull ivory colour. This is in fact perfectly normal in good, close range views – I once checked hundreds in the Ukraine!
• Although winter Caspian Gulls are often said to be white headed, they do in fact acquire grey head streaking just like other large gulls. It’s just that this streaking is so fine, so pale and so delicate, that it is often not visible except on very good views. Believe it or not, both the birds illustrated above had this streaking, but it normally manifested itself as a light dusting of grey that was not immediately apparent.
• It is also worth remembering that there is complete overlap in the bill measurements of Caspian, Herring, Yellow-legged and Lesser Black-backed Gulls.

Just before we left Minsmere, a third Caspian Gull dropped in, completing an excellent couple of hours of educational gull-watching!

At Least we got there in the end ...

By Keith Vinicombe

Whether you are a good birder or a bad one, finding a rarity always involves a large dollop of good luck, and this was brought home to me last week on our annual October visit to Scilly.

The first few days had been unseasonably hot and sunny, with most birders wandering around the islands in their shirt sleeves. On Monday 3 October, we set off for Tresco with no coats or waterproofs, confident that the heat wave would continue. However, half way across to the island, the mist rolled in, the wind got up and the temperature plummeted. By the time we disembarked at New Grimsby, it was, well, horrible.

Nevertheless, spirits soon rose with the discovery of a new Lesser Yellowlegs and three Pec Sands on the Great Pool but, as we continued to shiver, all I could think about was getting back to St Mary’s for a nice hot cup of tea. In one of the hides, I bumped into Robin Mawer, who told me that a stint had been seen briefly earlier in the morning. Apparently, it was thought probably a Little Stint.

Having given the yellowlegs a good grilling, we decided to yomp across the island to catch the early boat back to St Mary’s. However, half way to the quay at Carn Near, somebody told us that the Little Stint was showing at the eastern end of the Great Pool. I soon found it and set up my telescope. The trouble was, it was right on the opposite side of the pool, somewhere in the region of 200 m away. As I stared at it through the scope, it struck me that there was something not quite right about it. It showed noticeable pale bases to the third row of scapulars, rather like a worn juvenile Semipalmated Sandpiper, and I couldn’t see a mantle V. However, its overall plumage tone was quite a rich, almost chestnutty-brown, quite wrong for a Semi-p.

The only other possible alternative was Least Sandpiper, but that fitted even less. Least Sand has a Pectoral Sandpiper-like breast band and yellowy or greeny legs. This bird had fairly distinct patches on the sides of the breast and obviously black legs. In addition, it eventually turned to reveal a white V, albeit a rather weak one towards to the rear of the mantle.

This is what it looked like (screw up your eyes and imagine it at 200 m range):

Note the patch on the sides of the breast and the black legs.

Moving on a bit further, I found a small group of birders – including some very experienced Scilly locals - also grilling it. In a quick exchange of views, we all agreed that it had to be a Little Stint, and so off I rushed to catch the boat.

The following morning, there was a mega-alert on the pager: Least Sandpiper on the south beach on Tresco. Off we sped back across the water, but this time suitably kitted out for the inclement weather. By the time we got there, the bird had relocated to the eastern end of the Great Pool, to the exact spot where we had seen yesterday’s Little Stint. A quick look through the scope and my heart sank – it was the same bird. This time, though, we had the sense to walk down the southern side of the pool and watch it at ranges down to about 20 m, where it was clear to see that it was indeed a Least Sand.

At close range, it had a very finely streaked breast band – indeed, just like a Pec Sand – but what surprised me was that the background colour to the breast was pure white. This meant that, at any distance, the central part of the band was more or less invisible. The other thing was that its legs were heavily caked in sticky black mud. At times, though, chunks fell off to reveal the true colour below: olive green.

This is what it looked like up close:

Least Sandpipers really are reminiscent of a ‘mini Pec’. Note the narrow pale eye-ring, the fairly solidly streaked crown with no ‘split supercilium’, the complete breast band, the lack of obvious mantle Vs, the greeny legs and also the tiny primary projection beyond the tertials – juvenile Little Stint has a long projection of two or three primaries (although often shorter on adults).

Although I can justify dismissing it as a Little Stint, I can’t forgive myself for failing to check it out properly. If only I’d walked down the other side of the pool and given it a proper look! But I was cold, fed up, hungry, and rushing for the boat. That’s where the luck comes in – or, rather, the lack of it! But the episode also served as a reminder to follow your instincts, and always make certain before dismissing an even slightly odd looking bird.

PS Congratulations to my old mate Dick Filby though for sussing it out the following morning … don’t you just hate him!

White Wagtails – an easy ID shortcut

White Wagtail (Scilly, 21 Oct 2009). Autumn birds like this typically look
smart, having completed their moult before migrating. Photo: Steve Young.

Pied Wagtail (Seaforth, Lancashire, 4 Sep 2003). This rather dishevelled
female is undergoing a longer wing and body moult. Photo: Steve Young.

Although most birders don’t have many problems separating Pied and White Wagtails in spring, the two seem to cause a lot of confusion in autumn, when grey-backed juvenile Pieds confuse the issue. However, there is a very simple fact that gets overlooked in the separation of the two forms in autumn, and which renders the identification of White Wagtails at this time of year very straightforward.

Birds need to be in tip-top condition when they migrate, not only in terms of their fat reserves and general health, but also regarding their plumage. Moult does not take place during migration, as this would put a strain on the bird and would also impact on its aerodynamics, thus reducing its flight efficiency. Although some birds, such as adult waders, may suspend their moult during migration, most migrants complete their post-breeding and post-juvenile moults prior to migration. This means that most migrants are in completely fresh, neat and immaculate plumage when on their autumn migration, and this is particularly true of passerines.

Pied Wagtail is much more sedentary than White Wagtail and, like many essentially resident species, it has a rather protracted autumn moult. To confirm this, Birds of the Western Palearctic (Vol V) states that, in a non-migratory population of Pied Wagtails in southern England, the average duration of primary moult was estimated as 76 days, with an average start of 16 July and an average completion date of 30 September. Body moult more or less covered the same period. However, in migratory White Wagtails in northern Finland, the moult starts on 8 July (on average) but they take only 46-48 days to complete their moult. This means that, by the end of August, these high-latitude White Wagtails will have completed their moult and be ready to migrate south. Unfortunately, there is no data in BWP for Iceland, from where most of our migrant White Wagtails originate (at least those in western Britain). However, it is clear from my own observations in Somerset that White Wagtails in autumn (which usually appear from the first week of September) have already completed their post-breeding or post-juvenile moults, whereas the local Pieds are still in obvious moult well into September.

White Wagtail (Aswan, Egypt, 15 Oct 2005). Moult is completed prior to
migration, so plumage should appear immaculate. Photo: Dominic Mitchell.

Pied Wagtail (Seaforth NR, Lancashire, 12 Sep 2003). In contrast, Pied
takes longer to complete its moult, and appears scruffy. Photo: Steve Young.

The important point to make, therefore, is that in late August and September migrnt White Wagtails are always in newly moulted, ‘clean’, immaculate and fresh winter plumage, whereas local Pieds are still looking scruffy, ‘moth eaten’ and often dishevelled. As far as the young birds are concerned, in late August and September, you are in fact comparing first-winter Whites with Pieds that still retain a significant amount of their weak and fluffy juvenile body plumage. Such birds have black breast patches, whereas first-winter Whites have already acquired a neat and contrasting narrow crescent-shaped necklace across the lower throat/upper breast. In addition, this stands out as it contrasts strongly with the almost completely white underparts. On adult Whites, the necklace is thicker.

Pied Wagtail is a darker, sootier grey on the upperparts (adult males are largely black above), but the important feature of autumn Pied is its extensive dark sooty-grey flanks. White Wagtails have white flanks, with just some restricted pale grey confined to the sides of the breast, around the bend of the wing. The white flanks are readily apparent in flight and this allows even flying birds to be identified with some degree of confidence.

To sum up, autumn White Wagtails look clean, neat and immaculate; they are pale grey above, with white flanks and a neat and contrasting black necklace across the lower throat/upper breast. September Pieds, on the other hand, are rather scruffy and moth eaten, a result of their active moult. They retain significant amounts of black on the breast, they are a dark smoky-grey above and they have extensive smoky-grey breast sides and flanks. To put it simply, if you see a scruffy White Wagtail in autumn, then it probably isn’t one!

I would stress that the above relates to observations in western Britain, which involve migrant Icelandic White Wagtails; I have not studied autumn White Wagtails in eastern Britain.

Another Citrine

Juvenile Citrine Wagtail (at sea near Shetland, 7 August 2011). Note the ear-covert surround and double wing-bars, and compare with the images from Seaforth below. Photo: Julian Bell.

Citrine Wagtail is always a good find in Britain, but discovering one offshore must be a once-in-a-lifetime experience. Julian Bell was at sea on his way back to Peterhead on 7 August after working offshore west of Shetland when this dapper juvenile Citrine wagtail landed on board. It was only present for a short time, but long enough for Julian to capture several close-up images, including this excellent flight shot.

The at-sea location of the Citrine Wagtail, south of Shetland.

Citrine Wagtails: different strokes

By Steve Young

The first of the two Citrine Wagtails (photo: Pete Kinsella)

On the evening of Friday 28 August, Pete Kinsella found an odd-looking wagtail at Crosby Marina, next to Seaforth LWT reserve, Lancashire. Attracted by its Citrine-like call, his excitement increased when he saw the head pattern, but his was tempered by the bird’s thin wing-bars and the slight buff tones to its mantle. He took a few shots, half dismissing it as an aberrant wagtail of some sort, or possibly a hybrid. It was only seen briefly by one birder the next morning, and by Pete again briefly on the Sunday.

That same day, Gavin Thomas, Chris Gregson, Pete and I continued to look for the bird. We had no luck until Gavin went to search a different area, and a few minutes later rang to say he had heard it. We joined him and, sure enough, a wagtail flew past and landed briefly, calling loudly. I picked up my bins and saw two broad wing bars and a perfect Citrine head pattern. But Pete exclaimed: “That’s not my bird – it’s a different one, a juvenile Citrine Wagtail!”

The second Seaforth Citrine, clearly a juvenile (photo: Steve Young).

The ear-covert surround is less well defined on this bird (photo: Steve Young).

Unbelievably, it was a 'real' Citrine, found while looking for the original bird! The latter wagtail was never seen again, but images were circulated and some of the responses lean towards a moulting female or first-year Citrine. Interestingly, the ear-covert surround looks to be more pronounced on that bird than on the second Citrine, which is clearly a juvenile.

Juvenile Citrine typically has bold wing-bars and head pattern (photo: Steve Young).

Compare the above Seaforth juvenile to this YouTube footage of another classic individual, taken by ethering at Marazion Marsh, Cornwall, on 2 September 2009 (check out more of ethering's bird videos here):

And here's a recording of a Citrine Wagtail call - noticeably more shrill and rasping than the classic Yellow Wagtail equivalent (though some flava wagtails from eastern Europe and the Balkans eastwards have a more grating call note):

Tern ID revisited - BTO videos

By Dominic Mitchell

Following Keith Vinicombe's earlier post on the identification of Common and Arctic Terns in spring and summer, the BTO has released a helpful video illustrating some of the key identification criteria for both species. These have the added benefits of movie sequences and sound recordings, and are well worth viewing as a basic refresher:

There's also a second helpful BTO ID video on Britain's other three breeding terns, Roseate, Sandwich and Little:

See the Bird ID section of the BTO website for more identification tutorials.

Which warbler species - or even genus?

By Dominic Mitchell

Mystery warbler on Corsica: can you name the species?

Sometimes it’s impossible to be certain of an identification in the field, even when prolonged views facilitate careful observation of the bird in question. In such situations, obtaining a comprehensive series of images may allow the ID to be resolved subsequently.

An excellent recent example of this involved an intriguing warbler found during a Bird Holidays tour to Corsica in May. The group was birding at Ile Rousse on the north-west coast of the island on 28th when they came across the mystery migrant. According to one observer, “there was no tail pumping and no call (although we only had 15-20 minutes on the bird). [It] always looked large, beaky and pallid, and we didn’t really pick up any rufous tones in the upperparts. It was quite a showy bird (for a warbler), with fairly clumsy movement through a small area of bushes and limited skulking – unlike most ‘Acros’ out of habitat on passage.”

He continued: “Although our initial thoughts were of an Olivaceous, there have been plenty of niggling doubts (especially with the long undertail coverts), and none of us who watched the bird, or any who studied the photos subsequently, have been 100 per cent happy with any firm ID. Western Olivaceous must be a vagrant to this area …

“A couple of things niggle me slightly; the photos seem to show a slight olive tinge to the upperparts, although this could be just the light conditions. The wings do seem to have some pale edging to the secondaries. However, comparing it to a definite Eastern from the same time of year … the bill shape does look better for Western (I think!).”

These comments and images were sent to Lars Svensson, who responded: “I, too, felt it looked plain and rather pale at first, leading my thoughts towards the Iduna species, in particular to Isabelline Warbler (‘Western Olivaceous’, this patently dull alternative name). And there seemed at first to be more than one primary emarginated on its outer web (which would make Reed and Marsh Warblers rather unlikely). But the more I look at it, the more I feel that other clues are more important.

“I can see no hint of paler outer edges or tips to the outer tail feathers, features which I think should have been visible to some extent on at least some of the images. This would speak against Iduna. I also sense there is a little too vivid tawny-ochre or even pale rufous tinges in the plumage for Iduna opaca. This would fit better with Reed Warbler. (But rules out a May Marsh Warbler, then invariably showing subtle olive tinges on mantle.)

“The primary projection is also a bit long for any of the Iduna spp. And the wing-tip seems to be made up of p3, with p4 a little shorter. In opaca this would be wing-tip pp3-4 with p5 slightly shorter. Also, an Isabelline would have had deeper emargination of p3, halfway in from tip to primary coverts, but on this bird the emargination falls opposite the tips of the tertials and secondaries, which fits best really with Reed Warbler. I don’t think there is more than a hint of a narrower web on p4, thus not a proper emargination (but this particular feature is difficult to assess) ... All considered, probably a slightly odd Reed Warbler.”

The Corsica warbler: annotations © Killian Mullarney

Eastern Olivaceous Warbler for comparison. © Killian Mullarney

The same images and observer comments were sent separately to Killian Mullarney who, having studied them, replied: “The impression I had of this bird was that it looked more like an Acrocephalus than an Iduna sp. However, pin-pointing precisely what creates this impression is the difficult part! I spent quite a bit of time analysing the photos … and comparing some of the critical details with my own photos of Eastern Olivaceous Warblers (a species I have gained a lot of good experience with in the course of regular trips to Lesvos over the past decade or so) and Reed Warblers.

“It is more difficult to resolve the really fine detail of primary edges and emarginations on the off-net photos than in my own shots [of other birds] because of the big difference in resolution. Still, I think we can make out enough to be reasonably confident of the bird's wing formula. Before I go into this I'd like to make clear that my instant impression that the bird looked better for an Acrocephalus had very little to do with the tiny details that I have concentrated on in the annotations. In reality, just as generally happens in a field situation, it is an accumulation of numerous (mostly indefinable) subtle and subjective features that make me think something is an 'X', or a 'Y'. However, as so many of these features are somewhat variable, subjective and show a considerable degree of overlap it really isn't much help to try to 'deconstruct' the bird in this way and make a case for an identification. It might work a little better in conversation, while looking at photos together, but it just takes too long to do in correspondence.

Problem birds require critical analysis. Annotations © Killian Mullarney

Looking good for Acrocephalus ... Annotations © Killian Mullarney

“I believe the Haute-Corse bird's wing structure clearly points to it being an Acrocephalus, as opposed to any species of Iduna. The original photos would probably establish this even more conclusively, but note that the wing point is p3 (it would be 4, or equal 3 and 4, in Eastern Olivaceous), and only one primary (apparently p3) is emarginated. In Eastern Olivaceous, 3, 4 and 5 are emarginated. Incidentally, with these small Acrocephalus especially it is often very difficult to see outer edge of p2, as it tends to lie very close to p3 and have a less pronounced pale edge that is easily lost if the resolution isn't pin-sharp. Likewise, p1 is often very difficult to see on Acrocephalus, because it is so short, whereas in good photos of Eastern Olivaceous it can be quite prominent and easy to see.” Killian’s annotations to the photos of the Haute-Corse bird illustrate the key ID features.

He added: “In addition to the wing formula, I think the overall tone and areas of contrast in the wing are distinctly Acrocephalus-like, lacking Eastern Olivaceous's somewhat lighter-edged greater coverts and remiges. Also, to my eyes, the undertail coverts are rather long and seem buff washed, pointing to Acrocephalus.”

Note: Iduna is a resurrected genus supported by some authorities for certain warbler species traditionally placed in the genus Hippolais.

Acknowledgements
Thanks to Paul Willoughby of Bird Holidays (see birdholidays.co.uk) and participants in the Corsica May 2011 tour for permitting the use of the images and comments featured in the post.

Identifying juvenile Yellow-legged Gulls

By Keith Vinicombe 

Juvenile Yellow-legged Gull (Rainham landfill, Greater London,
16 August 2011). Photo by Dominic Mitchell.

Identifying immature large gulls is not everybody’s cup of tea, but there is an annual influx of Yellow-legged Gulls Larus michahellis in July, mainly into southern Britain. The species was finally split from the familiar Herring Gull L argentatus in 2006, although most birders probably had it on their lists for a couple of decades before this!

Yellow-legged Gull is a common and familiar sight in the Mediterranean, and these large gulls have spread up the west coast of France and the odd pair now even breeds in southern England. If seen well, adults are readily separable from Herring Gulls by their obviously darker grey mantle and yellow legs. Before tackling juveniles, it is advisable to get to know the adults, so that you gain a good ‘feel’ for the species.

The Yellow-legged Gulls that arrive here in July are usually large, heavy and sturdy birds, with a large bill with a distinct gonydeal angle on the lower mandible. The males in particular can be very large and often approach Great Black-backed Gull in size and overall bulk. In fact, a few days ago, I actually watched one persistently displaying to a Great Black-backed! When scavenging on dead fish – a favourite food source – they are very much second in the pecking order behind Great Black-backed and dominant over both Herring and Lesser Black-backed Gulls.

Like Great Black-backed Gull, large male Yellow-leggeds appear heavy and ponderous in flight. Females, however, are smaller, as are Yellow-legged Gulls from western Iberia, which appear in south-western England later in the autumn.

In flight, Yellow-legged Gull has very long and pointed wings compared with Herring and, on inland reservoirs, they can often be picked out at some distance – even with the naked eye – as they patrol up and down on arched wings, about 30-50 m above the water’s surface, looking for fish.

Juvenile Yellow-legged Gull

Juveniles are much more difficult to identify than the adults, but the following photographs should shed some light on their identification. Simply look at the images and soak in the plumage and structural differences.

Juvenile Yellow-legged Gull (Chew Valley Lake, Somerset, 21 July 2011).
Photo by Keith Vinicombe.

Plumage-wise, the following are the main points to note:
• Yellow-legged is more similar to Herring than Lesser Black-backed in overall tone, being brown with whitish feather fringes.
• Note the very white background colour to the head, neck and breast.
• Note also the grey ‘mask’ extending back through the eye. This can be very obvious on some individuals and, when combined with the white head and neck, it can create an impression distinctly reminiscent of a juvenile Mediterranean Gull.
• The entire upperparts are mid-brown, with clear-cut whitish feather edges. In particular, there is little chequering compared with juvenile Herring Gull (see photo below).
• Note the plain brown tertials, with a neat white fringe to all the feathers. The tertials are much more similar to those of juvenile Lesser Black-backed Gull than juvenile Herring, which shows heavy chequering around the edges. Note, however, that some juvenile Yellow-leggeds do show pale ‘notching’ or chequering towards the tips of the tertials.
• The greater coverts – the band of large feathers that runs along the bottom of the closed wing – have plain dark bases, particularly towards the front of the bird, this forming a dark bar. Two points to be aware of: firstly, it should be noted that the greater coverts are often hidden by the fluffed-up flank feathers; and secondly, many juvenile Yellow-leggeds show quite noticeable chequering on the inner greater coverts (those towards the tail end of the bird).

In flight, three features are worth remembering: first, the pale ‘window’ on the inner primaries is less obvious than on Herring, but much more obvious than on Lesser Black-backed; second, the upperwing coverts contrast quite strongly with the black secondaries and there is often a ‘second’ darker bar along the outer greater coverts, in front of the secondary bar; and third, the underwing coverts are dark brown, more like Lesser Black-backed Gull than Herring. The following photograph of a first-winter Yellow-legged Gull (taken in March) illustrates these points.

Yellow-legged Gull (Chew Valley Lake, Somerset, 30 March 2011).
Photo by Keith Vinicombe.

It is also worth remembering that, being a more southerly species, Yellow-legged Gulls breed earlier than Herring and Lesser Black-backed Gulls. Consequently, being more advanced, they moult earlier at all ages. The settled bird shown in the first image above (photographed on 21 July) has already acquired a few darker and greyer first-winter scapulars.

Juvenile Herring Gull

The juvenile Herring Gull below (photographed in September) is similar in plumage tone to Yellow-legged Gull, but note in particular the heavily chequered wing coverts and the chequered fringes to the tertials. Also, it lacks the dark bar across the outer greater coverts, shown by Yellow-legged.

Herring Gull (Praa Sands, Cornwall, 15 September 2009).
Photo by Keith Vinicombe.

Herring Gull is much more heavily and uniformly streaked across the head, lacking the striking white background colour and the dark mask of Yellow-legged. In addition, it is a slightly smaller-billed and more compact bird, its shorter primaries producing a somewhat truncated rear end compared with the long-winged Yellow-legged Gull. In flight, it is a rather stocky, relatively short-winged gull with noticeable pale inner primary ‘windows’.

Lesser Black-backed Gull

Young juvenile Lesser Black-backed Gulls are dark and rather smoky looking compared with both Herring and Yellow-legged. They are densely streaked and the feather fringes are darker and buffer, contributing to the overall darkness and uniformity of their plumage.

Lesser Black-backed Gull (Chew Valley Lake, Somerset, 29 July 2011).
Photo by Keith Vinicombe.

Note in particular that, like Yellow-legged Gull, Lesser Black-backed has plain tertials with a clear-cut pale fringe (if present, any ‘notching’ is slight and confined largely to the tip). Like Yellow-legged, Lesser Black-backed also tends to show a dark bar across the outer greater coverts.

On average, Lesser Black-backed Gull is the smallest of the three species, with a shorter, weaker bill and a long, slim and rather attenuated appearance; the latter is caused by the long primaries – a consequence of the fact that, unlike Herring Gull, Lesser Black-backed is a long-range migrant, with most heading down to western Iberia and north-west Africa for the winter.

In flight, Lesser Black-backed Gull has long, slim wings – producing rather a slim, narrow-winged, rakish impression – and juveniles appear particularly dark and smoky. Juvenile Lesser Black-backed is, in fact, much easier to identify in flight than at rest. Note in particular the very dark underwings (with only a faint pale window) and very uniform upperwings. Most importantly, the black of the upper secondaries extends right across the inner primaries to the outer primaries, forming a completely dark rear to the upperwing. Juvenile Lessers are also darker and more heavily marked on the rump.

Common and Arctic Terns in spring and summer

By Keith Vinicombe

The separation of Common and Arctic Terns has traditionally been regarded as problematical, despite some landmark identification papers in the 1960s and 1970s.

Common Tern (location unknown, 14 July 2007). Think of Common as slightly larger, sturdier and longer winged than Arctic, without the very long-tailed impression of the latter. Photo by Steve Young.

Arctic Tern (location unknown, 23 June 2009). Arctic is narrower in the wing and longer in the tail than Common, and the underwing is very white. Photo by Oliver Smart.

Plumage
One of the easiest ways to separate adults is by the pattern of the upper primaries, this being dependent on two facts: first, on Common Terns, as the grey primaries wear, they become darker; in fact they are quite blackish when heavily worn; and second, Common’s inner primaries are moulted twice a year, whereas the outer primaries are moulted only once. This means that, in late summer, most adult Common Terns show an obvious contrast between the old, dark, blackish outer primaries and the newer, fresh, pale grey inners.

In contrast, adult Arctic Terns moult all their primaries only once a year (on their winter quarters) so that, when in Britain, the upper surface of all their primaries is uniformly pale grey.

The problem is that this difference is much less obvious in spring and early summer, when Common Tern shows much more uniformly pale grey upperwings. However, even then, there is still a contrast between the darkest of the old outer primaries and the adjacent grey inners. This manifests itself as a small dark wedge in the centre of the primaries.

This may be obvious, facilitating easy separation, but it must be stressed that it can be hard to see, particularly at a distance or in bright light. Furthermore, the problem of seeing the wedge can be particularly acute on spring seawatches, particularly when distant migrating terns are whipping past at some speed low over the waves.

But it can also be surprisingly difficult to see on mid-summer Common Terns flitting around over inland lakes and reservoirs. The upshot of this is that the potential for misidentifying adult Common and Arctic Terns is far greater in spring and summer than it is in the autumn.

Size and structure
The best way around this is to really look closely at any close-range spring or summer ‘Commic’ Terns that you see, so that eventually you develop a good ‘feel’ for them. As you become familiar with them at close range, you will gradually become much more confident with them at long range. At Chew Valley Lake, we regularly separate feeding birds at ranges of half a mile to a mile. However, we do have the advantage that inland birds usually come closer, so that their identification can be confirmed.

Compared with Arctic, I always think of Common Terns as slightly larger, longer-necked, heavier, sturdier, longer-winged birds with an easy, languid flight action. Although long tailed, they do not have the very long-tailed impression of Arctic Tern. To put it simply, Arctic Tern – with its shorter neck, rounded head, shorter, narrower, more sharply pointed wings and long tail – really does look Swallow-like in shape, an analogy that is not nearly as appropriate for Common Tern.

Another useful difference is that the narrower-winged Arctic Tern really does look ‘Persil white’ on the underwings, with a thin, but clear-cut black trailing edge to the primaries. In addition, when viewed against the light, all the under primaries are translucent. The underwings of Common Tern are a less pure white, with something of a slight silvery effect. Most importantly, the dark trailing edge to the under primaries is obviously thick and diffuse, readily apparent at some distance. When viewed against the light, only the newer inner primaries appear translucent.

Flight action
When feeding over fresh water, Common Tern has an easy flight action, whereas, to quote Rob Hume (British Birds 86: 217): “Arctic is more bouncy and at the mercy of the wind. Common has a fast, powerful downstroke, but a faintly lumbering look. Arctic is fluttery and butterfly-like, with a quick, snapped upstroke and a slower downbeat – it is easier to see the downstroke than the upstroke on an Arctic instead of the other way around.

For birders in the south, it must also be stressed that Arctic Terns are much less regular than Common and, as a consequence, it is a fundamental mistake to assume that you will be encountering the two species in equal numbers. Although in spring and autumn some Arctic Terns may head overland or tag on to flocks of migrating Commons, their more pelagic lifestyle means that they often turn up after strong westerly winds, particularly in September.

Lesser Yellowlegs: postscript

By Keith Vinicombe

After my previous post on a Wood Sandpiper giving rise to thoughts of Lesser Yellowlegs (see below) on my local patch at Chew Valley Lake, something really bizarre and somewhat spooky happened. Fast forward 10 days to 8 July and another Wood Sandpiper was reported at Chew Valley Lake. I went to see it, and guess what – it was really a Lesser Yellowlegs!

Lesser Yellowlegs (right) with Greenshank (left) (Chew Valley Lake, Somerset, 8 July 2011). Taken at 200 m distance, asleep and in rain and poor light, this photo nicely highlights the difficulties of identifying distant birds. Could you have identified this bird? © Keith Vinicombe.

Lesser Yellowlegs (New York, USA, 30 September 2007). If only all views could be this close! © Wwcsig (commons.wikimedia.org).

Blackcap calls – we’re never too old to learn

Adult male Blackcap: calls of adults and young are different from Garden Warbler. © Jakup Stanco (commons.wikimedia.org)

By Keith Vinicombe

One of the great things about birding is that, no matter how long we have been doing it, we continually learn new things.

On 24 June, I was walking along a track at Chew Valley Lake, Somerset, when I heard some soft, quiet calls emanating from some nearby hawthorns: a rather flat eeh, or slightly more disyllabic eeut, almost like a soft toy trumpet. I’d heard these calls before and I’d always assumed that they were part of the repertoire of juvenile Great Tits. However, as I shoved my head into the bush, I was surprised to find a brood of recently fledged Blackcaps and their attendant parents. All the years that I have been plodding around that lake, I had never before sussed this call!

Adult Blackcaps have a more familiar call, but a lot of people struggle to separate it from that of Garden Warbler, something that has always baffled me. Whereas adult Blackcaps give a hard and definite chet or teck, Garden Warbler gives a quite different repeated soft vit vit vit vit vit vit. A brood of Garden Warblers that I came across on 14 June was also giving a throaty, slightly rasping, eeup or eeip call, more similar to the juvenile Blackcaps (but probably stronger).

Garden Warblers give their contact call less frequently than Blackcap, but it is quite distinct once learned.© Steve Garvie (commons.wikimedia.org)

The song of these two species is also very different yet frequently confused, but is less relevant now as we near the end of the song period.

Wood Sandpiper and Lesser Yellowlegs – a cautionary tale

Wood Sandpiper (Rainham, Greater London, 14 August 2010). With its obvious supercilium and shorter bill, Wood Sandpiper is unlikely to be mistaken for 'Lesser Legs' in typical field conditions. © Dominic Mitchell

Lesser Yellowlegs (São Miguel, Azores, 15 October 2007). Seen well, this American species is distinctive. But at a distance of 500 m, against the light? Read on ... © Dominic Mitchell

By Keith Vinicombe

With the advent of modern field guides and birding magazines, it is easy to assume that we have the identification of most rare and scarce birds well and truly sussed. But every so often we hear of what appear to be, on the face of it, elementary mistakes being made, even by experienced observers.

This was brought home to me on Tuesday 28 June during a routine visit to my local patch, Chew Valley Lake in Somerset. An adult Wood Sandpiper had been seen there the previous evening, a rare June sighting in this part of the country. I relocated it during the afternoon at the opposite end of the lake, but the views were distant and it disappeared for long periods behind a stony spit, so I drove around to Herriott’s Bridge at the south end of the lake. I soon relocated the bird but it was still about 500 m away and, frustratingly, against the light. It was impossible to make out any plumage detail and, more importantly, leg colour. It consequently appeared an amorphous, featureless bird with pale legs.

However, as I squinted down my telescope, I gradually began to wonder if it really was a Wood Sand. Most obviously, it had very long legs, with particularly long tibia (between the ‘knee’ and the body). It was also long-necked and long-billed and, even more worrying, it showed a long, tapered rear end. It also strode around, feeding more like a shank than a sandpiper.

As I continued to watch it, I became more and more convinced that it had to be a Lesser Yellowlegs, and I tried phoning others who I knew were at the lake. Eventually, Richard Mielcarek appeared and we agreed he would continue to watch it while I tried to get closer views from a different angle. In best commando style, I managed to creep down a ringing ride through the reeds and set up my scope close to the spit. Frustratingly, the bird had vanished but, after a few minutes, it came striding round the corner. My heart sank: a bog-standard adult Wood Sandpiper (Wood Sand is in fact my favourite bird, and I have never before been disappointed to see one!).

Wood Sandpiper (location unknown, 22 August 2006). © Steve Young

I phoned Richard and returned to the bridge. He told me that he too thought that the bird looked promising for a ‘Lesser Legs’, as did one or two others who had by then also appeared. I should add that the reason why the bird looked so slim, elegant, long-necked, long-legged and so attenuated at the rear, was that it had sleeked down its plumage in the afternoon heat.

The point of the story is to reiterate the obvious fact that, no matter how much you think you know, you can always be thrown by birds seen in difficult circumstances - in this case long distance and bad light – and that misidentifications are not always the result of incompetence by the observers.

Episodes like this are, however, instructive, emphasising the need to make sure that you obtain decent views of a bird before you make that all all-important phone call to the bird information services. It also illustrates a human trait that has always concerned me: in the absence of strong evidence to the contrary, once you have set your mind on a certain route, it is in fact very difficult to stop, change your mind, and go down a different one. It also shows that even experienced birders can be confused by standard birds seen in less than ideal conditions – a lesson for us all!