Motacilla alba alba: A new subspecies of White Wagtail for Singapore?

By Alfred Chia.

I write further on my recent note on 10 February in the “Singapore Birders” FB group of a White Wagtail Motacilla alba of subspecies alba occurring in Singapore. The bird was seen & photographed by Lee Van Hien on 9 February at Neo Tiew Harvest Link. This subspecies is new to Singapore. Currently, we have three subspecies: the commoner leucopsis, followed by ocularis and the rarer lugens.

There has been suggestions that this is not an alba but a baicalensis subspecies instead.

Baicalensis was suggested because “the wing panel doesn’t have to be completely white early in the season  and the two white wing bars usually show as a starting point” while “the shape of the bib leaves no doubt, especially the two lateral extensions”. This subspecies “would also not be unexpected” (in terms of range).

Allow me to clarify and justify why this is an alba and not a baicalensis.

1. Alba is a known migratory race. The features of the wagtail that was seen & photographed fits a male summer adult alba: i) the large black gorget extending all the way to the upper throat (perhaps the primary diagnostic feature to differentiate between an alba & baicalensis) and neck-sides, including the lateral extension ii) two prominent white wing bars formed by the white edges to the median & greater coverts (contra “starting point” towards a “white wing panel”) iii) the black centres on the greater coverts iv) the “clean” white face and grey upperparts etc.
2. Baicalensis, in all plumages do NOT have a black upper throat but a white upper & central throat instead. Searches through Macaulay Library and the Internet reveal all baicalensis with white upper throat. This salient feature was unfortunately overlooked when suggesting the bird as a baicalensis.

3. Intergradation in its breeding range exist between alba and baicalensis, alba and ocularis and between alba and personata but there is no evidence as yet that such intergrades (especially with baicalensis) result in a black upper throat. Indeed, Alstrom & Mild (2003) indicated several times in the monograph that baicalensis can be separated from alba by its white upper throat.
4. On current knowledge, the nearest wintering range of alba is in the Indian subcontinent. It would thus be a very long-distance vagrant for an alba to be found in Singapore. However, such long-distance vagrancy cannot be ruled out entirely. Recent years’ long-distance vagrancies resulting in new country records should be noted. Singapore’s Booted Warbler Iduna caligata in December of 2017 and West Malaysia’s most recent discovery of same warbler species in February 2020 are cases in point. Co-incidentally, Booted Warbler’s hitherto wintering range was also in the Indian subcontinent!

In summary, perhaps the most important reason for an alba is the overwhelming features this bird has that distinguishes it as an alba. It is identifiable and should not be treated as an unidentified taxa. Baicalensis can be ruled out because they do not have a black upper throat in all plumages.

Acknowledgement:

Thanks to Lee Van Hien for sharing his sighting and allowing the use of his photographs.

References:

Alstrom, P., Mild, K. & Zetterstrom, B. (2003) Pipits & Wagtails of Europe, Asia and North America. London: Christopher Helm.

Kennewell, M. (11 February 2020) Facebook “Global Rare Bird Alert”.

Rasmussen, P.C. & Anderton, J.C. (2005) Birds of South Asia: The Ripley Guide. Vols 1 and 2. Smithsonian Institution and Lynx Edicions, Washington, D.C. and Barcelona.

Robson, C. (2000) A field guide to the birds of South-east Asia. London: New Holland.

Note: This record of White Wagtail Motacilla alba alba is pending acceptance by the Records Committee.