Wrong side of the river

Tale of the unexpected: an American Mink is mobbed as it breaks cover in Thamesmead, south-east London.

I made a rare trip across the Thames to ‘sarf’ London today, mainly with the aim of seeing the second-winter Iceland Gull at Crayford after a tip-off from Kev Jarvis. In that ambition I failed, the gull departing before I arrived on site. A fly-by first-winter Yellow-legged Gull was scant consolation, but having then heard from Kev that Rich Bonser’s Ferruginous Duck at Thamesmead had been seen again, I duly set off in pursuit.

It’s been some time since I navigated my way around the back streets of Thamesmead, as a result of which I eventually ended up at Thamesmere Lake East. There was no sign of the Ferruginous Duck, a fact that became less surprising when John Archer helpfully tipped me off that it actually frequented Thamesmere Lake West. While at the east lake, however, I caught sight of a small animal scurrying along the far bank of the lake. Getting the bins on it, I quickly realised it was an American Mink – a species I haven’t seen in the wild previously in Britain.

This introduced predator is a serious problem for breeding waterbirds and small mammals.

The mink forages along the lake bank before disappearing in dense vegetation.

As the mink broke cover and ran along a concrete wall, Black-headed Gulls and Carrion Crows immediately gathered to mob it. The creature foraged briefly along the lake bank before disappearing into deep vegetation. While pleasing to see something unexpected, it was at the same time alarming – American Mink are voracious predators, their presence often being associated with catastrophic declines among Water Vole populations and damaging impacts on gull and tern colonies, even on offshore islands.

Interestingly, it is the second sighting of this species along the Thames in London in the last month, Dave Morrison having photographed one at Beckton Works just across the river (conceivably the same animal as mink are strong swimmers, though it seems unlikely one would try crossing the wide breadth and tidal flow of the Thames). Hopefully, measures will be put in place to control this introduced predator, or the consequences for local wildlife could be severe. 

White-fronted Geese in the Ingrebourne Valley.

After that distraction I arrived late at the neighbouring lake, with the Ferruginous Duck having now retreated out of view into the reeds (as it apparently likes to do). My first Common Chiffchaff of the year and a couple of calling Water Rails were the only notable species, so I headed back to Crayford, failed again with the Iceland Gull (though this time had second-winter and adult Yellow-legged Gulls) and cut my losses by heading north through the tunnel. Saving the day bird-wise were two White-fronted Geese in the Ingrebourne Valley, always a good species to see in London (thanks to Dave Mo for the tip-off).

* Footnote: researching American Mink subsequently, I was amazed to learn that one recent estimate put the British population at 110,000 (England 46,750, Scotland 52,250 and Wales 9,750 – Mammals of the British Isles by Harris and Yalden, 2008). I don’t know the species’ status in London – comments welcome.

Where there's muck ...

I could think of no better way of spending last Friday than being surrounded by gulls for hours on end. With a major influx of Iceland and Glaucous Gulls taking place after last week's Atlantic storms, I was hoping for a white-winger locally, but in the event it was Caspian and Yellow-legged Gulls that provided the main interest. At least four of the former comprised a first-winter, a third-winter, a fourth-winter and an adult, with the last two both being ringed. The fourth-winter bird was gold-on-green 355P, ringed as a chick in Poland and found by Jonathan Lethbridge and I at Rainham RSPB 14 months ago but not seen there since - great to have it back for another winter.

Back for another season, this fourth-winter Caspian Gull was ringed as a chick in Poland in 2008.

Note the distinctive primary pattern with largely white-tipped P10, big white mirror on P9, grey tongues on P8 and P9 and solid black band on P5. The primary coverts still have residual black markings.

The adult Caspian was the metal-ringed bird I saw last month. Despite getting close shots of it, however, I haven't been able to read any meaningful ring detail - if you can make anything out from these images, please post a comment. I suspect it was ringed overseas, not least because most gull-ringing schemes over here seem to colour-mark birds.

Yellow-legged Gulls were almost constantly present, and I decided to photograph every bird for a complete record. I estimated at least 14 individuals across all age classes, but having sifted through more than 900 images and compared fine bill and plumage detail, I was surprised to discover a minimum of 24 birds - four first-winters, nine second-winters, four third-winters and seven fourth-winters/adults. The range of variation within each age class was also surprising, and when time permits I will post a selection of images.

Plenty of other interest included an adult graellsii Lesser Black-backed Gull from a new ringing scheme (details hopefully to follow), and a very streaky-headed third-winter Herring Gull with a strong brown wash to the greater coverts, grey tongues to at least P8 (probably to P9, not sure about P10), a solid black band on P5 and a rather heavily marked blackish tail band for its age. As is so often the case with gulls, plenty of follow-up research to do ...

Third-winter Herring Gull with heavy head streaking and brown-washed greater coverts ...

... note also the primary pattern and blackish tail band at this age.

UPDATE: It has been suggested from the ring type that the metal-ringed adult Caspian Gull featured above may have originated from the Ukraine or Russia - enquiries continue.

Out with the old ...

A few of the thousands of European Golden Plover at Cley NWT, Norfolk.

I spent the last three days of the year in Norfolk, but because of family commitments only managed to get out in the field for a couple of hours just before heading back to London for New Year's Eve. Having studiously ignored it on the last two trips up here, I therefore decided to do the decent thing and twitch the Western Sandpiper down the road at Cley. Surprisingly, there didn't seem to be many people looking, but I found it fairly quickly out on Simmond's Scrape; unfortunately it remained rather distant, hence the poor record shots below. Plenty of wildfowl, waders and more to enjoy in the limited time - here's a few pics to sign off with until I get out and about in 2012.

Cley's long-staying Western Sandpiper was conveniently present on arrival ...

... but always remained distant, and then flew even farther away!

One of the numerous Black-tailed Godwits on Pat's Pool.

An aberrantly marked dark-bellied Brent Goose among the hundreds present on the reserve.

Gulls galore

Adult gull showing characters recalling the atlantis form of Yellow-legged Gull (or Azores Gull, reflecting the range of true atlantis). This is the second such bird I've seen in London. Note the pattern and density of head streaking.

I managed to squeeze in the last gulling session of the year at my local study site yesterday, and it was well worth it on a number of counts. Top billing potentially goes to the streaky-headed adult Yellow-legged type which was reminiscent of the form atlantis. This distinctive subspecies from the Azores - arguably a potential split - is more strongly streaked on the head than nominate michahellis Yellow-legged Gull in the autumn, often appearing hooded at any distance. I have seen many thousands of atlantis on the Azores over the course of nine visits, and this bird immediately brought their distinctive heavily marked appearance to mind.

Take your pick - a sample of head patterns on atlantis gulls from the Azores.

The pattern of streaking is not the most typical, however, as many (at least those I've seen in October) seem less well marked on the nape and sometimes more so on the 'snout', so that the hood is neater and more 'even' in appearance. However, I have also seen birds like this, and the pattern fits within the description provided by Olsen and Larsson (2003): "In winter (Aug-Nov/Dec), head more strongly patterned than in michahellis, similar to Herring and Lesser Black-backed, but streaking even denser around eye and below gape, but fainter on hindneck. Azores (and a few Madeiran) birds have even stronger head-spotting and look dark-hooded at distance; hindneck sometimes unstreaked. Head is mainly white with narrow dark streaks around eye and well-scattered brown spots on crown, hindneck and ear-coverts (Madeira and Canary Islands populations)."

The red orbital ring is just about visible in this shot, as is the very pale iris.

Also notable about this bird was the mantle colour, which was a distinctly dark ash-grey - edging a little more towards the palest graellsii Lesser Black-backeds (one of which is perched in front, above). Unfortunately, it was not seen in flight, although some images of it preening give an indication of the wing-tip pattern:

The bird wasn't seen in flight, but here's one shot showing some of the wing-tip pattern.

I wonder what this bird would have looked like two months ago? Presumably even more streaked, and by extension more dark-hooded. Some Azores adults are white-headed even in October, as are the great majority of michahellis by December. A photo of a streaky-headed adult michahellis, taken in November in Worcestershire, is mentioned as "extraordinary" on the Gull Research Organisation website. I have already had some interesting feedback from Peter Alfrey and am taking more soundings on variation in michahellis to try and establish whether the Rainham bird could possibly fall within that, or whether it is a better match for atlantis. More soon, I hope.

Adult michahellis Yellow-legged Gull yesterday - in typically white-headed condition in late December.

Among the many other interesting larids yesterday was a striking, long-billed and rather dark first-winter Caspian Gull (below). By amazing coincidence, among all the thousands of gulls in the area, it was also found independently and photographed by Paul Hawkins - small world:

Smart it may be, but this first-winter Caspian Gull is already looking heavily worn on the wing coverts.

A second-winter Yellow-legged Gull assumes the position.