On 20th January 2013 Forest Ang sent in the image below with a note: “This swiftlet has a nice patterned tail feathers. (Not sure it is common but strange to me). I have seen swiftlets flying and gripping onto wall with the tails pressing hard on the wall as leverage to balance themselves. I would think the tips were worn out from the constant pressing/rubbing of the tail end against the abrasive wall. Can anyone confirm this?”
Field ornithologist Wang Luan Keng was consulted and replied: “…the tail feathers are rather strange. I’ve never seen anything like this before. Let me ask my friends at the Burke Museum [of Natural History and Culture located at the University of Washington campus in Seattle] first.”
There are faint traces of chestnut red on the forehead and throat, indicating that it cannot be a swift or a swiftlet. And the presence of white on the tail feathers, although mostly worn out, points to the possibility of a Barn Swallow (Hirundo rustica). Forest subsequently sent another image of the bird, although no well focussed, showing the row of distinct white spots across the tail (below left). House (Pacific) Swallow (Hirundo tahitica) similarly has this white spots as the image by Amar clearly shows (below right) – LINK.
Amar confirmed the bird to be a swallow, although he wrote, “The longer I watch [the image], the more variation there appears to be. IDs are not all that easy, even for common birds. I presume [the bird was] seen in Singapore? Location matters for ID.” The presence of a black band at the throat led Amar to conclude that it should be a Barn Swallow. KC concurs with Amar. The bird was actually photographed in Penang, Malaysia.
However, both were wondering about the unusual pattern of the tail feathers – whether due to wear and tear or deterioration due to microorganisms.
The answer to the unusual pattern of the tail feathers was revealed by Chris Wood, Collection Manager of the Bird Collection at Burke Museum: “The bird in the picture is a very worn barn swallow replacing its remiges. The tail feathers wear more where they are white, because melanin strengthens the feathers. That’s why many white birds have black wing tips, because that is where they get the most abrasion. A very cool pattern in this particular bird! Swifts do get worn feathers, but each tail feather has a thick, stiff rachis for pressing on walls.“