A diverse weekend on the Thames

​March is as good a time as any to be out checking London's gulls for unusual visitors. There's always plenty of turnover at the numerous sites we keep an eye on, but especially so at this time of year as birds are very much on the move. As such, it can be particularly hit and miss along the Thames.

Rich, Dante and I met up at Greenhaven Drive, Thamesmead, on Saturday morning and after an hour's bread chucking got the feeling that, in the mild and spring-like conditions, that it wasn't going to be a 'hit' day. Aside the usual posse of Yellow-legged Gulls – 12 in total here throughout Saturday – there didn't seem to be all that much doing, so we decided to relocate to Erith Pier.

2cy (top) and 3cy Yellow-legged Gulls, Thamesmead, 7 March 2020

Erith is another site that suffers from patchy form in the winter months – those glory days of late summer 2019, when the surrounding river was swamped with Yellow-legged Gulls and it proved such a reliable bastion for close Casps, seemed a long time ago. Despite plenty of birds about, we'd seen nothing after the best part of an hour and so it was a bit of a surprise when Dante authoritatively announced: "Iceland in the melee!"

A small bird, this dainty, dove-like glaucoides is a very similar but nonetheless different juvenile to that seen at Thamesmead earlier in the year (which was also found by Dante at Erith). It had been at Rainham on a couple of days in the week, so it wasn't hugely surprising to see it come in and chow down on the sliced wholemeal. Naturally, views were decent, if a bit frustrating for photos, and it even had the decency to pose on the famous jetty for a short period.

Juvenile Iceland Gull, Erith Pier, 7 March 2020

Buoyed by this, it was back to Greenhaven Drive for high tide. As is normal, it took a while to concentrate birds and it was only after a half-hour or so, just after Rich left us for afternoon family duties, that the first Caspian Gull came in. A first-winter with strongly marked scaps and distinctive covert moult, I quickly recognised it as a bird I'd seen on Rainham tip on 28 January but not since.

2cy Caspian Gull, Thamesmead, 7 March 2020

A short while later a second arrived, a year older this time. Quite crisp and pallid in appearance, it only had the faintest residual markings on p10 but otherwise looked pretty nice.

3cy Caspian Gull, Thamesmead, 7 March 2020

Final stop of the day was Jolly Farmers at Crayford, which has been more miss than hit this winter. However, among the big numbers of gulls present (perhaps the most we've seen here this winter), two different second-winter Caspian Gulls were found, including the returning P:895 – the first time I've seen it since at Rainham in early December.

After the success of Saturday, hopes were high for Sunday. And it really felt like Greenhaven was going to come into its own at any moment, with more large gulls there than any of us had seen previously. But, despite lots of turnover and hundreds of Herrings, we could only muster a handful of Yellow-legged Gulls. Such is the fickle nature of London gulling.

A 2cy Yellow-legged Gull with a particularly narrow tail band at Thamesmead, 8 March 2020

In fact it was just as we were packing up that bird of the day appeared, a near-pristine adult Mediterranean Gull. This superb bird transpired to be sporting colour rings (as this species so often is!) and the red ring had us excited – ZHJ9 was a Czech bird! This is the first Czech Med Gull that any of us have seen, and the data indicates that it was ringed as a chick at the nest near Šenov, in the far east of the country, on 8 June 2017. So, a young adult only in its third winter, and the final of nine gull species seen over the weekend. Not bad at all, and a good advertisement for March gulling in the capital.

Adult Mediterranean Gull 'ZHJ9', Thamesmead, 8 March 2020