The Caspian Gull challenge

Even some of the keenest birders struggle to get enthusiastic about gulls. Large gulls take four years to reach their adult plumage, and transition through a range of plumages that can require feather-by-feather examination through a telescope to nail the identification. And then there are the 'splits'. Twenty-five years ago, just one 'herring gull' was recognised across Europe and western Asia. That was initially split into two species: a northern one (which we have nesting in North Wales) and a southern one, across the Mediterranean. And then in 2007, this southern population was further divided, into a (western) yellow-legged gull and (eastern) Caspian gull.

A handful of dedicated gull enthusiasts spent lots of time looking at landfill sites and estuaries in southeast England, and realised that Caspian gull occurs more frequently in Britain than had been realised, especially in the Autumn, when they disperse away from their breeding grounds in southeast Europe. At the same time, gull-watchers in Poland and Germany, noted that Caspian gulls were not just increasing as an autumn visitor, but were staying to nest along the Baltic coast.

Why am I mentioning all this? Because gull identification is not easy, and it's been a moving game. Anything written about large gulls in Europe more than five years ago is probably already out-of-date. Caspian gull hadn't been recorded in Wales until a couple of years ago, but this morning what we believe to be the fourth national record was found on the reserve by local birder Marc Hughes. There's no single feature to confirm the identification, you need to see a combination. We felt that this one looked good for a Caspian gull, but did it all add up? May is not a typical month to see Caspian gull in Britain, and Marc's and my collective experience of the species here is about half a dozen birds - none of them in May!

Marc grabbed a few digi-scope photos on his 'phone while I was scanning through images on the web, trying to find one that looked like 'our' bird. We were about 90% certain, more so when it lifted into the air and we could see its underwings and tail. Unfortunately, it carried on lifting into the air, circled high and headed east. Marc tweeted a photo, and several birders with far greater experience of Caspian gulls immediately confirmed our belief: a second calendar year bird. It still has to be submitted to the Welsh Records Panel, but we're feeling quite happy that it's the fourth for Wales, and a first for the reserve.

If you really want to know more about Caspian gull ID, there's an excellent paper in the journal British Birds. It will either leave you wanting to take up the challenge of seeing one. Or never wanting to look at a subadult gull again.

Other than that, what else have we seen here this week?

Migration is still in full-swing, with hundreds of swifts, swallows and martins feeding over the lagoons this morning. Wheatears continue to be seen most days, the majority now the larger Greenland race, while a few white wagtails are still on the saltmarsh. We've had more whinchats than usual this Spring, the most recent on Monday (8th), the same day as a redstart and yellow wagtail. A blue-headed wagtail was seen during last Saturday's guided walk (6th)

Small numbers of waders are heading north, with whimbrels still seen daily, and a couple of curlews today, the first for a couple of weeks. Five black-tailed godwits fed on the lagoons today (Saturday 13th), while little ringed plover has been seen a couple of times this week. A flock of 200 dunlins was unusual last Saturday (6th), while the best wader of Spring may prove to be a wood sandpiper on Friday 5th

Sandwich terns have been in the estuary most days for the last fortnight, unusual for this time of year, and a pair was even seen mating. Around 250 pairs are already back at Wales' only nesting colony, the North Wales Wildlife Trust-wardened Cemlyn Bay, so perhaps our numbers will reduce as they head to Anglesey.

There are several mallard broods around the lagoons, and we still have pairs of gadwall, teal and shoveler here - they could be worth keeping an eye on. Our pair of great-crested grebes displayed with the full weed-dance. And then promptly left! Better news for little grebes though, with at least one nest, and probably a second.

Warm afternoons have brought out the butterflies: orange tip, common blue, green-veined white, speckled wood, peacock and small tortoiseshell, but we've yet to record our first dragonfly. A colony of tree bumblebees has set up home in the pile of cut reeds next to the Bridge Pond. And on sunny afternoons look out for the nomad bees that are living inside the clawdd wall just outside the Coffee Shop. One species is Marsham's nomad bee (a great photo here by Jonni Price) but we think there's a second species too - we're just awaiting confirmation of its identification, as there are a couple that look almost identical.

Caspian gull - easy, compared to bees!