Is It or Isn't It?

Most birders will be at ease with the idea that not all birds can be identified with certainty. Regular seawatchers, for example, will be used to recording 'commic' terns, and will frequently leave distant auks, and even divers or skuas, unidentified. The balance of probability may well suggest that Great Northern is far more likely than Black-throated, but the bird will still go down as 'unidentified diver' because that is the safest call. When you cannot see diagnostic features, mere probability is not good enough.

As an aside I should mention that there are a few birders who will be able to identify absolutely everything they see by jizz alone. But such birders are either dodgy or red-hot (you decide) and we're not going to be talking about them any more. No, this post is about you and me, the everyday birder.

So, birds being unidentifiable is a concept with which most of us are comfortable in certain circumstances. However, the notion is not so easy to swallow when the bird is right there in front of you, giving crippling views. Just occasionally though, the everyday birder is faced with a situation where an easily-viewable, well-photographed bird might not be safely identifiable. And when that happens, every fibre of our being screams in protest, because such a bird simply must be identified. So when might this happen? Well, there are a few scenarios, but I'm going to pick just one, because it is painfully relevant right now...

Gulls. More specifically, putative Caspian Gulls. Even more specifically, X78C.

In THIS post some experienced gull-watchers had reinforced my view that the bird was a Casp, and unsurprisingly I was delighted. I am acquainted with several other very capable birders down here in the southwest who, while perhaps having less first-hand experience with Caspian Gull, are thoughtful, analytical observers, and I value their opinions. Matt Knott had already expressed his view that certain features suggested Herring Gull gene influence, and it was Matt's idea to seek some help from the London contingent. But since their input it's all gone rather quiet. Are my fellow SW birders in agreement with their diagnosis, or not...?

Well, until very recently I didn't know. And then Steve Waite got in touch. I think Steve knows I'm always up for a debate, so here's a potted version of his take on this bird...

• The hybridisation issue with Casp, and how they could look, is unknown.
• How can we be sure that the chequered greater coverts, dirty underparts and less-than-impressive size are actually okay for Casp? And to say they are okay is a guess. 
• We don't know what the bird will look like as an adult. [Steve showed me an example of a bird which had been deemed okay for Casp as a first-winter, but showed obvious hybrid traits in adulthood.]

In a nutshell there are too many red flags for Steve's liking, and for him it's in the hybrid zone. He then apologised for disagreeing with me, as we never have before on a gull's ID. At which I smiled, because if I'm honest I needed challenging on this. Here's why...

In some areas of bird ID I am a bit cavalier. Not with a poorly-seen bird. No, I'll almost always let them go. A late-May probable Short-toed Lark on Beer Head still grates, but I really didn't get enough to claim it. But with birds like X78C this tendency comes out. An obvious hybrid like some of the vile Aythya duck things I have no problem with, but something like this gull brings out the worst in me. For some reason, "Have it!" is my default position.

I'm in danger of going the same cavalier route with the Sibe Chiff issue, which is exactly why I am trying to research it properly. I hope to reach a point where I can safely call a pale winter Chiff a tristis, but I'm not there yet. Not quite.

Anyway, Steve's challenge to my complacency has prompted me to revisit something I should have thought of ages ago...

British Birds 104 - December 2011 - pp702-742

This superb 41-page paper not only analyses the various plumage and structural traits of Caspian Gull, but also provides a scoring system for each, so that you can assess individual birds. In addition it suggests a threshold score, outside which a bird may not safely be identified as Caspian. Assuming my photos provide enough detail I shall duly put X78C through this process, and report back.

Personally I enjoy being challenged on things like this. Hopefully I am open-minded enough to respond positively, and I'm always willing to learn. I try to avoid presenting myself as some kind of 'expert' on anything, because it must be very hard when you have to climb down from such an elevated position to acknowledge a mistake. In my book, good debate drives knowledge.

With grateful thanks to Steve for prodding my conscience thus.