Having looked at the literature and evaluated published identification criteria using photos of ijimae Sand Martin and fohkienensis Pale Martin on the web, I am less optimistic than I was that the two species would ‘stand out’ as being obviously distinct from each other. I think the problem of differentiating them may be as challenging as that of identifying the ‘brown’ swiftlets.
Although they may be useless for identification, what these flight photos show is that the birds were in moult. Almost all had replaced the inner 7-9 primaries, and many had started tail moult, replaced tertials and a varying number of wing coverts. Their state of moult would therefore be consistent, I would have thought, with the Hong Kong Pale Martins, which have mostly completed a full moult by the time they arrive there in April. It’s also worth noting that new feathers are greyer and less warm in tone than the old ones.
Going on what I learned in the previous two posts, my starting point for trying to identify these bird is to look at tarsal feathering.
Though over-exposed (so don’t read too much into the apparent paleness of the breastband) and distant, this bird, photographed on 2 Feb, had the most extensive tarsal feathering of any bird I saw, a continuous band all the way up the rear tarsus to the tibio-tarsal joint.
At the lower end of the ‘hairiness index’ were birds like this – very sparse and short, but still, the continuous ‘comb’ or ‘fan’ of feathering from base of hind toe to mid-tarsus.
This poses a potentially troublesome question – assuming these are all Pale Martins, how variable is this tarsal feathering? Is it affected by wear? I would expect burrow-nesting birds to do quite a lot of scraping in and out of their nest-holes resting on their tarsi.
Now here’s something interesting!
This bird lacks the continuous comb of feathers up the tarsus, but instead has two well-developed ‘feather spurs’ on an otherwise bare tarsus, like the Sand Martins here or here perhaps? The other interesting thing is that the legs are dark pink, more this colour (a Sand Martin).
I discovered 2 or 3 of these birds, unfortunately only when going through my photos, and there were no other frames to show whether there is a correlation between leg colour and tarsal tuft shape. Still, compare the blackish toes and deep pink tarsi of the bird above with the birds showing fan-like tarsal tufts below.
Hmm – is leg and toe colour significant? Something to check in the future!
The owner of the dark red legs and blackish toes above.
So – what do I think? All very tentative still, and I’m putting these images and ideas up here to give others the chance to prove me wrong, but … if forced to put my head on the block, I would suggest that the majority of the birds I photographed are Pale Martins, with the possible exception of this one bird which had ‘plume-like’ tarsal tufts, and possibly one or two others which had dark pink legs/blackish toes, which could very well be Sand Martins.
I can recommend a visit to see these martins. Hopefully they’ll stay a month or so longer and we may yet get to see them complete their moult before they leave. Let me know if you need directions.
Oh, and by the way – don’t be fooled by these…
as someone else has been! These aren’t Pale or Sand Martins, they’re juv Barn Swallows! Note the long bill and different head shape. Brown and white juv Barn Swallows are not so rare in this part of the world, but the plumage variation has not yet found its way into many field guides.