Monday 31 August 2009

American Black Tern, 30/8

Late on 28th, news broke of an apparent juvenile American Black Tern (surinamensis) at the slightly unexpected setting of Farmoor Reservoir (Oxon). Due to various reasons, I sacked off going on the 29th, playing it cool and eventually going on the Sunday morning.
The bird wasn't exactly difficult to find. Farmoor is great; it's really easy to see everything on a couple of concrete bowls. Sure enough, the obliged for the next hour or so (albeit at distance) as I viewed from the causeway, along with my fellow Bank Holiday Sunday dudes. The bird itself was splendid; a wonderful marsh tern with dusky flanks and underwings, dark grey rump and upperside and grey (as opposed to black) crown. What helped (and indeed made the record so remarkable) was that both confusion species, both 'European' Black and White-winged Black Terns, were present alongside it:

Left to right: leucopterus in flight, niger (middle) and surinamensis

I guess it will be some time before (if ever?) such a trio will ever show up on the same body of water again. Being able to compare the three side-by-side revealed a few things, not least the size and structure of surinamensis appearing more akin to that of leucopterus. In flight, it also seemed to resemble its White-winged cousin more than Black, and spent much of it's time associating with the former. This allowed for fantastic comparison between the clean, crisp White-winger and the much darker, duskier American Black. So, perhaps not a good candidate for a split (you only have to look at the DNA to realise that), but certainly a charismatic and distinctive subspecies that I would certainly recommend seeing.

Above: Upperside...
... and underside

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