There is now a reasonably large collection of images of both fohkienensis Pale Martin and ijimae Sand Martin on the web. I’m making a couple of assumptions in saying this – that birds on Japanese websites were photographed in Japan and are ijimae, and that the birds photographed in Hong Kong are all fohkienensis. If this is the case, there is a reasonable sample from which to make comparisons.
For a start, I want to test the characteristics mentioned in Robson 2008 as being distinctive of fohkienensis Pale Martin.
Slightly smaller and smaller-billed
Absolute size cannot be compared, but relative bill size can.
In these close-up photos, Pale Martins do seem small-billed. However, the difference is not obvious, and, with subtle differences in head angle and lighting, it is very hard to be certain of. I’d say this is at best a weak supporting field character, unlikely to be conclusive even with photos. Differences may show up on in-hand measurements though.
Slightly shallower tail fork
I can see no consistent differences between taxa in this feature, and plenty of variability within both species due to age, wear and moult. For example, birds missing central tail feathers appear to have a perfectly forked tail when it is held closed. There may be average measurement differences, but I can’t see this being a useful field characteristic distinguishing the two.
Upperparts paler and greyer
It’s certainly true that almost all photos of Pale Martins from Hong Kong show cold grey-brown upperparts with no warm tones. See 1. here 2. here and 3. here, On the other hand, all these photos are taken in April and early May when the birds are in crisp, fresh plumage, with paler edges to the body feathers. What might these birds look like when they are in more worn plumage? Two birds photographed in early May 4. here (labelled Sand Martin) and 5. here show warmer tones and look darker and more uniform overall, presumably as a result of having lost the pale frosting to the feather edges.
Sand Martins in fresh plumage also look rather pale grey-brown – see 1. this juvenile photographed on 26 August, compared to 2. a darker grey-brown adult on 27 Aug. 3. A series of pictures of birds at a breeding colony on 26 June give the impression of rather darker grey-brown birds than the Pale Martins in Hong Kong. There are couple of other upperpart shots of worn adult ijimae 4. here and 5. here.
Dark grey-brown upperparts in April might point to Sand rather than Pale Martin, but on present knowledge, I doubt whether upperpart colour can be considered diagnostic. Moult timing may yet prove a helpful distinguishing character.
Underparts less clean white
Creamy wash on belly and undertail-coverts
The only photos of Sand or Pale Martins I could find showing signs of this are of a bird or birds photographed at Tianjin, China 1. here and 2. here. These seem to have a pale creamy wash to the underparts. The photos are labelled Sand Martin, but I’m not sure if that’s the correct id.
As far as I know, no birds in Hong Kong have shown a creamy wash to the belly and undertail-coverts.
Breast-band paler but neater, often faint in centre
This is certainly true of some of the other races of Pale Martin – see this photo of a tibetana Pale Martin photographed in Hong Kong.
At least one photo of fohkienensis also shows this characteristic well. Many of the fohkienensis Pale Martins in Hong Kong show a narrow, pale breastband, especially those in pristine fresh plumage (see 1. here (bottom pic) 2. here and 3. here). However, others show a darker, broader and more distinct band (see 4. here, 5. here and 6. here).
Ijimae Sand Martins can also show a narrow breastband (see 1. here (note the paler central breastband on this bird) and 2. here) or a broader one (such as 3. here and 4. here). In most cases, these appear dark and distinct, but this, like other tonal features,may be affected by feather wear. Birds in fresh plumage might show a paler breastband, such as this bird.
On present evidence, it does seem that a pale breastband is a pointer to Pale Martin, while a dark breastband does not necessarily eliminate fohkienensis Pale.
Dark smudging in centre of breast/upper belly indistinct or lacking
Judging from photos, this is a variable feature in both species, from practically none at all (Pale and Sand) to a small smudge (Pale and Sand) which can sometimes be distinct (Pale, Pale, Pale and Sand).
I would say that the absence, presence or extent of this smudging is of less usefulness than the paleness of the breastband itself.
Pale tertials and inner secondaries can contrast strongly with rest of the wing.
No idea what this is about, and no evidence I could find of this in photos.
In summary, of the features given by Robson to separate fohkienensis Pale from ijimae Sand in the field, I would suggest that, while none alone are diagnostic, the following are of some practical use:
- A pale, narrow breast band
- Pale grey-brown upperparts in April/May
- Small-looking bill
All of the above are best judged from good quality still photos.
Another possible distinguishing feature put forward is that the wingtips of Pale extend beyond the tail tip when at rest, while those of Sand fall level with or short of the tail tip.
I find the photographic evidence is inconclusive. A lot depends on the posture of the bird. There are enough pictures of Sand Martins showing wingtips extending beyond the tail (e.g. here, here and here) and of Pale Martins showing wingtips not extending beyond the tail tip (e.g. here, here and here) to make me think this is probably not useful.
Loskot (2006) asserted that the extent and nature of tarsal feathering is a consistent differentiating feature between Pale and Sand Martins, though he did not apparently examine any fohkienensis Pale.
You need to get a good photo of a perched bird at the right angle to see the tarsal feathering well! Nevertheless, there are some samples on the web.
Pale Martin: This bird shows very obvious tarsal tufts. The two photos of the bird alighting here also show a dense fan-like tuft extending from the base of the rear toe half way up the tarsus. Less easy to see against the pale background, this bird also shows dense feathering reaching halfway up the hind tarsus.
Sand Martin: It’s not easy to see the detail, but this bird does not appear to have a dense tuft of tarsal feathering. Again, it’s hard to see against the dark background, but this bird and this bird seem to lack extensive pale tarsal feathering. Though out of focus, the raised right foot on the right hand bird here lacks extensive tarsal feathering, which would surely be evident if present. This photo clearly shows one or two single longish feathers above the base of the hind toe, quite different from the dense fan-like tuft on Pale Martins in Hong Kong. A similar characteristic is shown on the front bird here – two single longish feather tufts. This bird is a possible ‘fly in the ointment’, as it appears to show a Pale Martin-like tuft behind the left leg. However, the photo isn’t clear enough to be conclusive, and it only appears to be visible on the outer side of the tarsus – the inner side of the right left appears bare – so I’ll reserve judgement on that one!
In conclusion, photographic evidence of fohkienensis Pale Martin and ijimae Sand Martin seems to back up Loskot’s assertion that the shape and extent of tarsal feathering is a strong differentiating character. While it’s true that this is rarely visible in the field, it isn’t impossible to see, so I propose that it represents the best diagnostic field character we have, based on present knowledge. At least, that’s my working hypothesis!
Now at last, I am ready to look at answering the question which is the tiitle of the post – that’ll be Part 3!