Hi Ivor,
I looked into Mangrove and Varied Honeyeaters a bit during
the 90s and early 00s when I was living in Townsville. To answer your question
is more complicated
than you might think. My methods were very simple; I looked at them at as many
locations as I could in NQ, and recorded some plumage details particularly on
the
underparts, throat and head. NO captures, no DNA, not even any photos, just
plumage
notes.
In summary, I found almost exclusively pure Mangrove
Honeyeaters from the mouth of the Ross River (south side of Townsville)
southwards
to Gladstone at many locations. I found almost exclusively pure Varied
Honeyeaters
from Rowes Bay (north side of Townsville) north to Cape York and PNG. The
furthest north I ever found a Mangrove Honeyeater was in the small recolonising
areas of mangroves at South Townsville, near the port. This is about 5 km in a
straight line from Rowes Bay where Varied were resident, and there is no
suitable habitat in between, so they effectively abutted at Townsville.
The exceptions were interesting:
1). Julian Ford collected 2 hybrids at “Cleveland Bay” in
the 1980s. Both Ross River and Rowes Bay are in the huge Cleveland Bay but
Andrea Griffin was with Julian and she told me they were at the mouth of the
Ross River. I never saw a single hybrid or anything that made me suspicious,
anywhere in Cleveland Bay, though of course I might have just missed them.
2). 40 km or so South of Townsville at Cape Cleveland and
Cungulla, there were only Mangrove Honeyeaters, except on a couple of occasions
I
saw a single Varied with the Mangroves somewhere in the township of Cungulla. I
suspect it was just the one bird that I saw repeatedly. This was the only
location where I ever saw the 2 species together.
3). In 1989 or 1990 at either Lucinda or Halifax (about 100
km n of Ross River) Kath Shurcliffe showed me a population of hybrids. Later
when I was looking into it I couldn’t find this locality again, and only got
insufficient
views of honeyeaters in this area, so I was never able to verify the earlier
sighting for myself.
My data set doesn’t prove anything, but here is my wild and
reckless hypothesised explanation:
Mangrove and Varied Honeyeaters are closely related (sister
taxa). They evolved from a common answer relatively recently when some
historical barrier split the
ancestor’s range into 2. They are now in ‘secondary contact’ after the barrier
broke down. Since they both have linear distributions tied to coastal mangroves
this is a rare example where the secondary contact effectively occurs at a
single
location, rather than across a broad front. They can and do hybridise, but
mostly they do not. Varied Honeyeater is expanding southwards and displacing
Mangrove as it goes. The individual Varied I saw at Cungulla living with
Mangroves was, at that time, leading the charge, an unwitting scout. The 2
hybrids collected at Ross River were love children of the battle front at that
time. Varied had not one that battle and had retreated slightly, at least
temporarily. The hybrid swarms at Lucinda or Hallifax (if they exist) are
isolated historical
remnants from a time when Varied swept southwards through there displacing
Mangrove
as it went.
That speculation aside, if someone looked at the genetics I
wouldn’t be surprised to find either: a) a complex mix of secret hybrids
throughout, even though they look like one species or the other; or b) there is
no
difference between them genetically. My ‘explanation’ would likely prove too
simple.
So I would expect that birds north of Townsville are still
Varied. Your yellow washed birds at Ross River might also be Varied, advancing
south once more, or they might be hybrids or they might
even be juvenile Mangroves. Get some photos if you can.
Thanks Mike Carter for bringing this to my attention.
Cheers,
David James
Sydney
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