Thursday, 18 April 2013

Another week, another patch first

Arctic Tern at Alexandra Park this morning: the first-ever site record.
Spring finally uncorked itself in London this week, a flood of migrants pouring in since the weekend and - initially at least - in unprecedented numbers. The closest of my two London patches, Alexandra Park, benefited big time in the form of a fall of Northern Wheatears four days ago, anything between 10 and 30 birds moving through during the day. I wasn't able to get there then, but I resolved this morning to put in an hour and a half before heading into the Birdwatch office. I'm glad I did.

Note the pattern and translucence of the primaries on the upperwing (above) and underwing (below).
Initially unpromising, with just the current crop of migrant Common Chiffchaffs, Willow Warblers and Blackcaps barely audible over the clatter of building work and a freshening south-westerly wind, I gave up the scrub as a lost cause and headed for the reservoir on the east side. A quick scan  revealed a tern among a few Black-headed Gulls towards the far bank, and I expected it to be our first Common Tern of the year - they are regular in spring and again from late summer. But immediately this individual rang alarm bells.

The jizz of the bird felt wrong for Common, its shape with relatively compact head and bill, 'forward-placed' wings and long rear all pointing to Arctic Tern, as did its buoyant, graceful flight. A closer look at the wing pattern was the only other evidence I needed, a long, narrow dark trailing edge to the often translucently white primaries confirming the identification.

On London's large, deep-water reservoirs in the main river valleys, Arctic Tern is more expected in spring. But here in suburban north London, on this relatively tiny water body, it is exceptional - there are no previous records. So I immediately rang around the park regulars, left voicemails and sent texts, and before too long the bird was also seen by David Callahan, Gareth Richards, Gabriel Jaime and Alan Gibson. I found it at 08:03 and it must have just arrived, as Bob Watts checked the reservoir on his normal early circuit some 30 minutes or so previously. It stayed until 09:21, when Gaz and Gabriel watched it head off east. It was the 177th bird species recorded in Alexandra Park and the third new addition to the list this year, after my Great White Egret in February and Bob's Slavonian Grebe last week. No new species were added in 2012, so we are well ahead of target!

The Arctic Tern with a second-calendar-year Black-headed Gull for direct comparison.
My Canon EOS 7D is currently in for service, so for these record shots I experimented with a Canon SX40 HS, a superzoom that I reviewed for Birdwatch last year. A dip-feeding tern in strong winds against variably glaring water, dark banks and bright sky was a good test for this model, flagging up the differences between a high-spec DSLR and a bridge camera. As record shots they are acceptable in confirming the identification, the camera just about coping with fast-changing lighting situations and the rapid, erratic movement of the bird - in normal field conditions, it performs much better. I've cropped these images and adjusted the levels a little in Photoshop, but left them unsharpened to avoid introducing more 'noise' (texture might actually be a better description). I also shot some short video sequences, and will aim to post one tomorrow to see how good the HD output from this camera looks.

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