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Friday, 20 November 2009

The Identification of ASIAN HOUSE MARTIN

There has yet to be a confirmed record of ASIAN HOUSE MARTIN in the Western Palearctic but it is a strong contender to occur. On the back of yet another odd bird in Israel, the following information largely gleaned from Surfbirds forum contributors is most useful.

Some excellent images of Asian House Martin are published here http://www.hkbws.org.hk/BBS/viewthread.php?tid=9527&extra=page%3D1

Identification expert Paul Leader has also very kindly provided this very useful summary of defining characteristics based on his wealth of experience with the species.

The separation of Northern (Common) and Asian House Martins is relatively straightforward on good views. This posting is actually quite timely from my point of view: I found the first Northern (Common) House Martin for Hong Kong only yesterday, which has been well seen and photographed. It was present with about ten Asian House Martins, of two subspecies.

The following apply:

Structure: Asian is tiny compared to Northern, overall length being about 80% of Northern and clearly smaller body size. The tail is clearly shorter which results in Asian looking far more compact. The tail fork difference is obvious (except when dealing with moulting birds), with Asian having a very shallow tail fork which results in the tail appearing square when slightly spread. It is worth noting that the Northern in HK was of the taxon lagopoda, which has a more shallow tail fork than nominate, yet the fork depth difference was always obvious.

Rump: The rump patch on Asian is small and rather square looking (beacause more of the longer uppertail coverts are black than in Northern HM), and often sullied grey, especially in the southern taxon nigrimentalis. It seems that northern birds (i.e. nominate dasypus) have a cleaner, whiter rump than southern birds and are more similar in rump colour to Northern. The rump patch on the HK bird was massive compared to the Asians present, such that the bird could be picked out on naked eye views. However, as this bird was of the taxon lagopoda in which all the upper tail coverts are white, this difference would be less obvious in a western European context. However, I still think the rump size difference would be obvious.

Underparts: The underparts of Asian are very dusky grey, except for the throat which is contrastingly white. This is obvious in the field. Nominate dasypus is probably darker below than southern birds although the literature is contradictory on this issue and this needs more research. However, the gleaming white underparts of the HK Northern was strikingly different to the underparts of the Asians present.

Underwing coverts: These are always black(ish) on Asian, and are darker than the rest of the underwing. On Northern (on eastern birds at least) the underwing coverts are grayish or brownish and show little if any contrast with the rest on the underwing. However, in dull conditions, the underwing coverts of the Northern at times looked darker than the rest of the underwing, so this feature should be used carefully. However, in good light the uniform grey underwing and underwing coverts was obvious (especially on photos).