Monday, 15 August 2016

Long-billled Dowitcher

I snuck off back up to San Gu this afternoon for further looks at the Pale Sand Martin Riparia diluta, but, although there were plenty of hirundines, none were landing on the road as they had been doing the previous afternoon so I had no idea if the bird was actually still around. I typically find a small number of these annually in the first few days of September, so there are doubtless still more to come. The trip was not a total waste of time, though, as I also managed to find my second Long-billed Dowitcher Limnodromus scolopaceus of the autumn, this time an almost pristine summer-plumaged adult. I got reasonable shots of it with my small lens and could have done much better, that is if the 'Tour de France' (an old man and two kids on bicycles) hadn't chosen to come through after I had waited an hour or so for the bird to wander nearer. The passing commotion flushed everything back to whence it originally came, but did allow me to get some flight shots.

What the flight shots did show was just how different this individual was from the one at Jiang Jun a couple of weeks earlier, as the wing was as yet completely unmoulted. I wondered if moult timing might be useful in dowitcher separation and it turns out that it is, but that the characteristic of primary moult may be one that is unidirectional in nature. Long-billed Dowitchers choose to moult at staging posts whilst on migration, moult into winter plumage, and then continue southwards, so any bird in active wing moult here in August (like the Jiang Jun individual) is necessarily a Long-billed Dowitcher. Unfortunately, it does not follow that the reverse is true (i.e. that any bird not in moult in August must be Short-billed Dowitcher Limnodromus griseus (hence unidirectional)). Though I did have a half-hearted go at turning this into one, it is not an especially short-billed individual, has wavy lines rather than spots on the neck sides, and has white-fringed rather than golden-buff wing coverts. It also seems more likely that a vagrant Short-billed Dowitcher would be of the more distinctively-patterned Pacific form rather than of the interior continental prairie form (the most similar to Long-billed Dowitcher). I assume that this bird has quite literally 'just arrived', and that if it is going to stay for any length of time it will drop its inner primaries within the next few days. Anyway, all of this made for an interesting diversion for the afternoon if nothing else. Above photos taken at San Gu, Tainan County 15/8/16.

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