Following the report of the observation by Richard Baxter on Cocos (Keeling)
Island, Edwin Vella asked 'Is the macronyx Yellow Wagtail a full species? If it
is, what other species of Yellow Wagtail have been split?"
Well as always, it depends on the taxonomy you choose to follow. Even the
recent Pipits & Wagtails, the ultimate reference by Alstrom & Mild, (2003)
Helm, wasn't definitive. It treated the Yellow Wagtail as a single species
with, if I can count, 13 subspecies, some with various forms, but then said
molecular data suggest they should be split into two groups, 'Western' and
'Eastern' forms, OR into nine or more species! So far as Australia is concerned
only the three subspecies comprising the Eastern group have so far been claimed
or recorded. These are tschutschensis (which absorbs simillima), taivana, and
macronyx. Alternatively these could be regarded as three separate species. So
we await the next Christidis & Boles.
Unfortunately, macronyx resembles thunbergi (of the 'Western' group) so closely
that it 'is not diagnosable by plumage, morphometrics or voice' (A & M page 285
and elsewhere) but DNA data says it is different! Either or both could occur in
Australia. Since thunbergi has a more northerly breeding distribution, I think
it a more likely vagrant to Australia especially for an occurrence in May as
they migrate later. However, Schodde & Mason (1999) CSIRO, followed Mees
(1982), in accepting macronyx from central Asia as the more likely taxon, so
changed the initial identification of a Yellow Wagtail seen at Richmond (NSW I
suppose) (Australian Birds 1979). Both winter in the Oriental region and
according to Alstrom & Mild, thunbergi breeds not only further north but also
further east than macronyx. S & M considered thunbergi a northwest Eurasian
form and therefore of unlikely provenance. Not so apparently.
Fortunately, Richard has numerous excellent photos of this beast.
Unfortunately, I dipped! BUT GOT HIS CHINESE POND HERON now believed to have
gone. I'd seen it within 29 hours of Richard's gratefully received call to my
home in Victoria!
30 Canadian Bay Road
Mt Eliza VIC 3930
Ph: (03) 9787 7136
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