Friday, 26 August 2011

Farmoor Terns

I've come to realise that one of the aspects that I enjoy most about birding is working through difficult bird ID issues. I've talked in the past about the difficulty of gull ID and why I therefore enjoy the challenge so much. Well this week I've had the opportunity to look into another tricky area of birding ID, namely juvenile terns. There have been some good terns turning up at Farmoor this week with arctic, common, black and little all present to varying degrees. In fact on Wednesday morning there were at least 30 black terns (which buggered off during the day) and a juvenile little tern which was present all day until about ten minutes before my arrival for my now regular Wednesday evening gulling spot. I had been looking forward to getting to grips with the various terns and was most disappointed to find nothing more than a couple of juvenile common's by the time I got there. To put a further damper on things it was rather windy and this made peering at distant gulls in the roost rather problematic so all in all it was a less than satisfactory outing. I did manage a passable shot of a juvenile dunlin along the causeway shoreline. That's one nice aspect of Farmoor: you get far closer to dunlin than you ever would on Port Meadow. I am always amazed at just how small they are when you see them close up. But that notwithstanding, it had been a disappointing evening's visit: even the number of yellow-legged gulls was noticeably down on last week.

Juv. dunlin on the causeway (click to enlarge)

The (or another) little tern was present for Thursday evening and reported again first thing on Friday morning so mid morning I decided that a return trip to Farmoor was called for. In addition the weather was wonderfully overcast and drizzly and looking ripe for something juicy to drop in. I arrived to hear and then see a whimbrel flying off to the east which was a nice start and boded well for the visit. Steve Young arrived at about the same time as I did and we passed a very pleasant couple of hours watching the comings and going on the reservoir. There was a greenshank and a few common sandpipers and dunlin on the wader front and the little tern was still about as was a juvenile black tern and a "commic" tern that we spent some time discussing. When watched in flight, it's relatively clean wings and what appeared to be a relatively short bill (Steve even took a photo of it with the bill looking nice and short) had both of us (and others both before and after us) convinced that it was an arctic. However when it landed on the barley bails the bill looked a lot longer and eventually, with the help of Roger Wyatt who had arrived by then, we came to the conclusion that it was actually a juvenile common tern. One key ID feature for separating juvenile common and arctic terns which I'd not been aware of before is that commons have a thin wedge of grey which extends from the back down into the tail which is absent in arctic. This ID feature was actually relatively easy to pick out, at least compared to things like bill length and jizz which in flight and at a distance are very difficult on juvenile terns. So if you get a juvenile "commic" with a grey wedge then it's a common (or a juv. roseate which ID we did entertain briefly though that has a much more marked "saddle").

I put together a bit of video from the various snippets of footage that I took whilst I was there.

As well as this nice ID snippet I had the opportunity to study the other terns more closely. It was interesting to note just how small the little tern looked especially in flight. It had a very characteristic fluttery bat-like flight and long swept back wings reminiscent of a swift. In addition it had quite a contrasty paler "W" thing going on in the wings (รก la kittiwake) which was rather noticeable. I was also rather taken at how small the black tern looked next to the common tern, and in fact at one stage got briefly confused by the size into thinking it was a second little tern before the squared-off rump and dark colouring (and Steve!) all put me right.

Digiscoped videograb of the black and the little terns on the barley bails

All in all it had been a most informative Farmoor trip, getting to grips with some of the harder birding ID issues and I came away having thoroughly enjoyed my visit which had more than made up for the Wednesday disappointment. In the continued absence of my patch, I think that I may very well be paying more visits to Farmoor over the coming weeks.

Random Farmoor cormorant

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