The Bronze-Cuckoo paper – "Phylogeography and taxonomy of the Little
Bronze-Cuckoo (Chalcites minutillus) in Australia's monsoon tropics" was
published in the Emu (2011, Vol 111:113). It is pretty heavy going.
However, I had some very interesting correspondence with Dr Naomi
Langmore, one of the authors, before the paper was published. In
layman's language, the results showed clear separation between the three
races minutallus, russatus and barnardi but only by a very small degree
of divergence i.e. all three taxa were at the very early stages of
speciation. The results apparently also suggested that the "three
populations were reproductively isolated".
This seems to go against the claim that there is extensive hybridisation
between minutillus and russatus throughout the Wet Tropics and Cape York
Peninsula (e.g. Ford, 1981 - Hybridisation and migration in Australian
populations of the Little and Rufous-breasted Bronze-Cuckoos - Emu
81:4:209). Neither does it seem to translate in the field. Regardless of
what DNA suggests, those "hybrids" seem to be seen mostly within the
more extensive habitat of russatus - which could well be an age stage or
variation within this form ? This does not seem to be evident to any
extent in the open dry forest habitat (breeding range) of minutillus on
the western edge of the Wet Tropics.
I suspect these so-called hybrids have been determined by examining
skins without consideration of habitat or locality (from where
collected) and without any consideration that the so-called hybrids may
be an age stage or variation - in russatus especially. This is quite
evident in Ford's paper where he seemed to automatically assume that
these were hybrids, giving no consideration to them being age stage or
variants. This seemed to have then prompted Ford to claim extensive
hybridisation - which later seems to have been automatically adopted by
others.
There are a number of important morphological differences between the
two forms which do not conform to extensive hybridisation. These include
a very distinct habitat preference difference, a host species
difference, a hatchling difference, an egg colour difference. I also
think there is a subtle difference in voice. As an example of host
species fidelity - out at Mt Carbine which is in extensive dry open
forest and the habitat of minutillus and its main host species -
White-throated Gerygone, there is a small isolated area of remnant
gallery forest (rainforest) along a dry creek well away from the rest of
that forest. This is the usual habitat of russatus and its main host,
Fairy Gerygone which inhabits the gallery forest on the western side of
the Wet Tropics. There is a resident pair of Fairy Gerygone in that
patch of gallery forest. There is also an isolated pair of Gould's
Bronze-Cuckoo which parasitise that pair of Fairy G.
True, it is a problematic complexity but I have always been of the
opinion that the two northern Qld taxa were probably good species when
coupled with what appears to happen in the field. I think much more
field work needs to be done over and above lab work and the examination
of museum skins. I think the true answer is out there in the field
rather than in the lab or in a drawer of museum specimens.
I note that both forms are retained as species in the new "Cuckoos of
the World". I think that should be the case until proved differently -
or at least until variation/age stage is fully investigated.
I also think the assumption that Gould's is resident and Little is
migratory still has to be proved one way or the other - barnardi is
definitely migratory - it occurs through the Wet Tropics in winter,
often through the coastal habitat of russatus - which again complicates
the situation.
Lloyd Nielsen
Mt Molloy, Nth Qld
www.birdingaustralia.com.au
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