Sunday, 7 July 2013

Crossness strikes again

Adult (or second-summer) Bonaparte's Gull at Crossness, London, today.
I ended my post yesterday with the stop-press news that a Bonaparte's Gull had been found on the Inner Thames at Crossness. It was still present today, so I had to make the awkward cross-city journey to 'sarf' of the river to spend some time with this third-ever London bird. And what a peach it was too.

The black hood reaching further down the nape and around the throat, as well as the shorter and more slender black bill and smaller size, are clear distinctions from Black-headed Gull (behind).
Bonaparte's Gulls in full breeding plumage are rare in Britain, most being seen in winter or spring - or, in the case of the long-staying bird this year at Oare Marshes, Kent, as first-summer (2cy) birds. There is speculation that the new arrival at Crossness may actually be a second-summer (3cy) on account of the tiny speck of black in its primary coverts.

The pale under-primaries are just about visible in this shot. Note also the pinkish-red legs.
The two previous London records of Larus philadelphia both also come from Crossness, and were as recent as spring 2012 (an older record, previously accepted, is now under review and expected not to survive). Might this latest bird be one of those two returning? The finder of the 2012 individuals, Rich Bonser, was there today at the gathering for this adult, as were Jono Lethbridge, Mick Southcott, John Archer, James Lowen and many others. While Rich and I were chatting, the finder of the latest Bonaparte's, Mike Robinson, also appeared. He played down the find, putting it down to luck, but should be very pleased with discovering such a notable American vagrant in arguably the month it is least expected to appear.

Obvious here in the centre of the frame, the Bonaparte's could sometimes go missing among the large and mobile gathering of adult and juvenile Black-headed Gulls at the sewage outfall.
This record is a reminder that Crossness is right up there with Rainham and Beddington as one of the top three gulling sites in London. As well as the three Bonaparte's Gulls I was fortunate to see the Franklin's Gull present here in April 2000 - neither species has yet appeared at Rainham or Beddington, though both have their own claims to fame. Such birds are a reminder to keep looking at gulls throughout the year, and to never give up.

Saturday, 6 July 2013

Summertime ...

Second-summer Yellow-legged Gull - a typical individual.
... and the gulling ain't easy. I'm sure that's what DuBose Heyward  meant to say when penning the lyrics to Gershwin's jazz standard. The supposedly warmest months of the year can be a challenge for followers of the larid faith, with the wintering flocks long departed, migration over and almost all adult birds back in their breeding areas. My Thames-side study site still has gulls, often hundreds of them, but sifting through the massed ranks of typically ragged, moulting immatures in dry and dusty conditions is not always rewarding.

A different bird of the same age - note, for example, the different covert and tertial patterns.
In my very limited time away from work projects in the last six weeks I've squeezed in just three short trips to keep an eye on the gulls on my patch. Yellow-legged Gull is my main target, and I've been monitoring the number of summering non-breeders, a few of which are shown here. The number present on 14 June was 15, rising to 17 on 18 June, when the first returning adult appeared. Today, 6 July, I was pleased to find 29 present, though just two were adults. Within a month, mature birds may dominate as more arrive from south-west Europe - this species is most numerous on the Thames in late summer and early autumn, with fewer in winter; by spring it's often hard to find.

Comparison of same-age Yellow-legged (left) and European Herring Gulls: note the former's darker, more solidly ash-grey upperparts, less chequered wing-coverts, 'cleaner' head and underparts, more adult-like bill pattern and yellowish legs. Although there is huge variation, Yellow-legged often looks more advanced at this age.
This morning's session was the most productive, with some 1,100 gulls of eight species present:

  • European Herring Gull: the most numerous species by a nautical mile. Today's gathering included what looked like a very worn, darker-mantled 3cy argentatus-type, but with pale yellowish legs.
  • Lesser Black-backed Gull: the second most numerous species, mainly comprising graellsii types but occasional darker presumed intermedius or so-called Dutch intergrade birds. Interesting colour rings noted on three individuals from different schemes - more news soon I hope.
  • Yellow-legged Gull: of the 29 present, 3cy was the commonest age class.
  • Black-headed Gull: initially 39 in one area, but numbers built during the morning to 100+, mainly on the wing catching flying insects.
  • Great Black-backed Gull: five individuals at most.
  • Caspian Gull: three today - my highest summer count. A small adult, presumably female, was seen well at close range, and there were at least two 3cy birds.
  • Mediterranean Gull: sometimes difficult to get on the Inner Thames in summer, I was delighted to pick this species up on call while driving past a large group of hawking Black-headeds. On inspection, there proved to be three individuals - two pristine breeding adults and a hooded 2cy bird.
  • Common Gull: rarest of the rare in midsummer, just one 2cy bird present briefly before flying off.

A grab shot of a flying Yellow-legged Gull to show the distinctive combination of ash-grey saddle and blackish tail band below white rump and uppertail. Again, note the more adult-like bill.
Interestingly, there were no juvenile gulls of any species - the first young locally bred Herring and Lesser Black-backed Gulls can't be too far away, while fresh juveniles of the earlier-breeding Yellow-legged Gull should already be heading north towards Britain. I may not get a chance to visit again until August, by which time the gull landscape should look very different.

* * STOP PRESS * * After my Thames session this morning, news broke of a Bonaparte's Gull upriver at Crossness sewage outfall. A superb discovery by Mike Robinson, it represents just the third London record and could relate to one of the two 2cy individuals seen there in spring 2012. Well done Mike!


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