So four Arctic Terns (2 adult, 2 juv.) were present at Frampton's sailing lake on Monday - the 24th. I went this evening to see if I could see them - it would be a year tick and a lifer.
I arrived at the lake at about 1800hrs, and immediately picked up on four Terns feeding over the lake. Two juveniles and two adults. Then it got hard. As much as I wanted to make these birds into Arctic Terns, I just could not. I'm no Tern expert, indeed I've never seen an Arctic Tern (thus I've no real world frame of reference)... but I really thought about this and I reckon they were all Common Terns.
Neither of the adults displayed the advertised grey wash on the breast, and so their cheeks did not seem contrastingly white. The primaries had more black on them than the distinct narrow bar one would expect on an Arctic Tern. Their bills were most definitely not blood red, and both had a clear black tip. I tried to convince myself that they had shorter necks, but not so. It wasn't inconceivable that their centre of gravity as they flew was towards the chest, but I don't see enough Common Terns to be sure of their jizz! I don't know how short the legs of an Arctic Tern actually are, but I reckoned these were too long.
So to the juveniles. I struggled with the head markings, but their bills both had a significant area of orange on the lower mandible (more than just the base). There was very little ginger-brown across the birds, though - which complicated matters. Both juveniles had pale inner secondaries and darker outer secondaries creating a pale patch on the wing. I would expect a Common Tern juvenile to sport this dark secondary bar - an Arctic Tern should recede to white along the edge. I saw them both perched, and noted the dark carpal bar was particularly obvious.
All this is cribbed from books and text, sure, but it was all a match for Common Tern.
Finally, I do have one type of experience on my side... I know that if I am trying to convince myself I'm seeing the less-common bird (I couldn't describe Arctic Terns are 'rare'), then I'm probably not seeing it.
Boy do I hope nobody reports these birds as being Arctic Terns... but I have to fall on the side of Common Tern.
In the form of compensation, I got a great view of a nearby Kingfisher, and a noisy Green Woodpecker.