As one would expect, most are tschutshensis. Dark breast in some birds is
remnant of first year (1st basic) plumage. The bird with dark head and faint
supercilium may have some macronyx in it but I'm inclined to think such
individuals are more likely to be thunbergi/tschutschensis (t/t) hybrids or
even possibly more eastern tschutschensis. (There are photos from Broome by
George Swann of a similar bird.) Two reasons. Firstly, distribution of taxa
as shown in Alstrom & Mild's Pipits & Wagtails makes that cross more likely
than macronyx/tschutschensis (m/t) (whilst not ruling it out). Also perhaps
more likely because a t/t cross would be a longer distance migrant than an
m/t cross. In support of this long held belief, see Bell (1996) on leap-frog
migration in Yellow Wagtails in Journal of Avian Biology (thanks Simon). For
those without access to Pipits & Wagtails, in central Asia, thunbergi has
the most northerly range, breeding between ~60-75 deg N to as far east as
Kamchatka 160 deg E, then replaced by tschutschensis through to Alaska.
Macronyx is the most southerly breeding form extending north to the latitude
of northern Sakhalin 55 deg N. In central Asia, tschutschensis occupies the
intervening region except in far north-eastern china and Sakhalin which is
the domain of taivana.
Any way good luck Simon. You'll probably get a head-ache and make little
progress just like those of us who have gone before!
Mike Carter
30 Canadian Bay Road
Mount Eliza VIC 3930
Tel (03) 9787 7136
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