Western and Eastern Marsh-harriers in Singapore?

posted in: Raptors | 5

The images taken at Changi Cove by Lim Kim Chuah in the October 2008 issue of Singapore Avifauna were originally identified as Western Marsh-harrier (Circus aeruginosu). The identity was subsequent amended to Eastern (C. spilonotus) after David Bakewell pointed out the error.

In view of the above, Tan Gim Cheong made a detailed study and posted his disagreement with the identifications of the Western in BESG’s two posts. The first was posted in January 2009 on a bird seen in Pulau Semakau. The second was a bird sighted in Changi in February 2009. R Subaraj, who contributed both posts, has since clarified that the images in both were taken at Changi, as the raptor at Semakau was not photographed.

The two BESG’s images were subsequently sent to Dr Chaiyan Kasorndorkbua of Kasetsart University, Thailand, who is a recognised authority on raptors of the region. He has responded, stating that the bird in both images is a young adult Eastern Marsh-harrier:

“This is a young adult Eastern Marsh Harrier, brown-backed variant.

“Although, it looks alike the Western due to brown back and mantle, but note the wing tips (outer primaries, both on upperwing and underwing) are black barred and the thick white band on uppertail coverts. The Western normally does not have these, instead it has totally black outer primaries (not barred) and very thin white band on rump (if any). The white “rump” is a spilonotus genetic trait.

“In sub-adult and young adult, say 3-4 calendar year Eastern-marsh, the mantle and back can look similar to Western-marsh. This character will remain in such certain birds for few years, thus so called brown-backed variant. Though, I do not know if this variant will change to a typical plumage (of black mantle with white scaling) when (the bird grows older).”

In view of Chaiyan’s comments, BESG’s two postings on the Western, at Pulau Semakau and at Changi, have now been re-evaluated. Both birds should be Eastern, unless there is photographic evidence of the Semakau bird to prove otherwise.

The marsh-harrier complex in the genus Circus is among the most controversial issues within the Accipitridae. Thiollay (1994) treats the Western and Eastern Marsh-harriers as two separate species. Robson (2005, 2008) similarly supports the split. On the other hand, Ferguson-Lees & Christie (2001) regard these as two sub-species of the Northern Marsh-harrier (C. aeruginosus). The rationale? The sub-species interbreed where they meet in west and north Mongolia, producing offspring with variable intermediate characters. Well, if the two forms interbreed, they must be subspecies, not distinct species! But then, is there any evidence that the progenies are fertile?

Over in Singapore, Wang & Hails (2007) treat Western and Eastern as sub-species of C. aeruginosus. The Eastern was mostly recorded locally, with regular sightings since the 1980s. However, an immature Western was reported to be seen regularly at Changi by various observers since 19th November 2005, based on confirmation by Lim Kim Seng, Chair of the Nature Society (Singapore) Bird Group’s Records Committee. The bird was reportedly still seen in 2006. However, we have not been able to uncover how these purported Western sightings were identified.

Also, the pocket checklist issued by the Records Committee (Lim, 2007) supports the splitting of the species, reporting the presence of both Western and Eastern Marsh-harriers.

Considering the controversy currently raging, unless there are images to support the identity of the Western, we need to treat all such sightings as Eastern. After all, two experienced birdwatchers, Kim Chuah and Subaraj, have so far accepted the fact that they misidentified Eastern for Western.

In the meantime, Subaraj has indicated that “I am certainly not above admitting if a mistake in identification has been made by me as the learning curve should continue our whole lives. …we need to re-examine all Western Marsh-harrier records from Singapore, Johor or further north.”

Furthermore, Subaraj is of the view “that all Western records without images should be retracted and if there are no confirmed images, the species/subspecies should be removed from all checklists.”

Image of Eastern Marsh-harrier by Benjamin Lee.

References:
1.
Ferguson-Lees, J. & D. A. Christie, 2001. Raptors of the world. London: Christopher Helm. 992 pp.
2. Lim, K.. S., 2007. Pocket checklist of the birds of the Republic of Singapore. Nature Society (Singapore) Bird Group Records Committee.
3. Robson, C., 2005. Birds of South-east Asia. New Holland, London. 304 pp.
4. Robson, C., 2008. A field guide to the birds of South-east Asia. New Holland, London. 544 pp.
5. Thiollay, J. M., 1994. Family Accipitridae (Hawks and Eagles). In: del Hoyo, J., Elliott, A. & Sargatal, J. eds. Handbook of the birds of the world. Vol. 2. New world vultures to guineafowl. Lynx Editions, Barcelona. Pp. 52-205
6. Wang, L.K. & C. J. Hails, 2007. An annotated checklist of birds of Si ngapore. Raffles Bulletin of Zoology, Supplement 15: 1-179.

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5 Responses

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