Sorry for a late weigh-in on this thread. It is an extremely
interesting thread. Here is a warning that this post is long and technical.
I agree whole-heartedly with Jeff Davies's and Kevin
Bartram's posts that the Hamilton bird is a leucopsis form of Ninox from
Tasmania, based on the features they outlined. Last year there was an offline
discussion about the Ninox novaeseelandiae/boobook complex, the split of
Morepork, the status of the "red boobook' in the NQ rainforests, etc. I
went to the Australian Museum (AM) in Sydney with Murray Lord to look at skins
of small Ninox owls from Tasmania (leucopsis), mainland (boobook and ocellata),
the Wet Tropics (lurida), Lord Howe Island (albaria) Norfolk Island (undulata)
and New Zealand (novaeseelandiae). This is a complex group and the AM
collection does not hold the whole story. However, I got some insights and
generated some hypotheses to share.
Murry posted his photos of selected specimens on-line, and
you can see that the Gabo Island bird looks like the Tas birds. I don't have my
notebook (in storage) but the measurements fitted Tasmanian birds perfectly and
it was too small to be a mainland bird. There were 2-3 other specimens from
Sydney in the AM (all >80 yrs old) that also fit Tasmanian leucopsis on
plumage and measurements. I am convinced that Tasmanian leucopsis sometimes
migrate
to the mainland. However, there are many winter records of boobooks from Tas,
so it is not a total exodus. I even saw one in my yard in Hobart in the winter
of 1988.
Tasmanian leucopsis very closely matches NZ novaeseelandiae
in plumage and measurements. The functionally extinct Norfolk Island subspecies
undulata very closely matches both Tas leucopsis and NZ novaeseelandiae. These
three forms comprise a tight group that seemingly differs significantly from
mainland
Aus boobook and ocellata on plumage and measurements (by ‘significantly’ I mean
the variation within each group is obviously less than the variation between the
two groups). It is not a matter of degree, but a clear division, with no
intermediates blurring the distinction. Whether there is any point in
recognising ocellata as a distinct subspecies from boobook, I am unconvinced
(there is continual variation across the continent with no obvious place to
draw a line; however, I have not delved into this in detail). The extinct Lord
Howe I form albaria is a little different from all the others, but is most like
Australian boobok/ocellata. It certainly does not look to be part of the
novaeseelandiae group. It seems that Schodde & Mason (1997: Zool Cat Aus
37.2) made a mistake by placing albaria as a subspecies of Morepork N.
novaeseelandiae.
Some people advocate that there is insufficient evidence to
prove the trans-Bass Strait migration. However, I see no reason why they
wouldn’t
cross Bass Strait, it is hardly a shocking notion. I don’t believe that
presence of leucopsis-like skins from the mainland can be adequately explained
by postulating variation within mainland boobooks that has been overlooked.
Besides,
the evidence is difficult to deny. The eminent museum ornithologist Gerlof Mees
(1964, Zool Verh. 65:1-62) recognised 7 specimens of Tas leucopsis from Vic and
1 from NSW (all in winter), while McAllan & Bruce (1988 The Birds of NSW: A
Working List) listed 3 more from NSW. There have been several more in Vic since
then. Evidence of birds in migration are 3 specimens from Bass Strait (1 on On
King
I, 1 on Flinders I. and 1 at sea of the Hunter Is. (Mees 1964), 1 at sea off
Gabo I., Vic (in the AM) and a bird seen in a cave on Albatross Island, Bass
Strait, for a few days in Sep 1984 (Brothers & Davis 1985, Tas Bird Rep
14).
However, a much more interesting question is why would there
be a change of form across Bass Strait, rather than across the Tasman Sea (i.e.
why does leucopsis fit morphologically with novaeseelandiae instead of with
boobook)? How might this scenario have evolved?
Firstly, consider that the Tasman Sea has existed for over
50 million years and Bass Strait has existed for under 20 thousand years. The
ancestral
owls didn’t invade Australia and then evolve into a different species on NZ,
Norfolk and Tas. There must have been a double invasion. Perhaps the first
invasion saw ancestors of the novaeseelandiae group distributed throughout
Australia and NZ, but a second invasion saw them displaced on the Aus mainland
by
ancestors of the boobook group. Alternatively, perhaps novaeseelandiae and
boobook diverged into two species either side of the Tasman Sea and then the
ancestors
of leucopsis reinvaded from New Zealand to displace boobook in Tas (and the
ancestors of undulata colonised Norfolk Island from NZ). It could be that
leucopsis is closely related to boobook but resembles novaeseelandiae due to
similar environmental demands (convergent evolution). This could be tested
genetically, but my feeling is that this is not a case of convergence but s
case of divergence. Perhaps there are other explanations, but not that
leucopsis diverged from boobook when they were separated by the appearance of
Bass Strait.
I know of no other scenario where a Tasmanian animal or
plant is more closely related to a NZ one than to a mainland one. With all
respect
to Kevin, I do not see any parallel between Ninox owls and other candidate bird
splits across Bass Strait. I don’t mean there are no potential splits, but they
are not the same. (I’ll get to fantails soon, but first to Red Boobooks).
The NQ form lurida (the 'rainforest boobook' or 'red
boobook') in the Wet Tropics is really intriguing. The breeding range of lurida
is entirely encircled by the breeding range of the non-rainforest form the
‘boobook
and/or ocellata’ (b-o) and the two morphologically distinct with no overlap.
Lurida has been muted as a separate species on several occasions.
I have seen what I believe to be hybrids between lurida and b-o
either side of Paluma and possibly somewhere around the Atherton Tablelands.
Jeff
Davies is not convinced, and perhaps he is correct that they are just pure b-o
at
the darker end of the scale. Either way, these potential intermediates are
rare.
If there are no hybrids between lurida and b-o then lurida
is clearly a good species by any definition. However, even if there are a few
hybrids
but no general cline or jumble of intermediates then they also must be
different species. With few exceptions, it is technically not possible to have
sympatric subspecies with sharp boundaries in animals, because subspecies are,
by definition capable of hybridising when they are in contact. Hybridisation
will lead to a large number of intermediates and eventually a cline. The lurida
has such a tiny range with such a big border abutting b-o that the intermediates
would be more common than pure lurida, which is not the case. It might be argued
that the habitat difference keeps them separate and prevents hybridisation, but
I think this is incorrect because they would still hybridise extensively at the
margins of the rainforest unless they were reproductively isolated (which would
make them different species by any definition). It follows that lurida did not
evolve in situ in the Wet Tropics but is a remnant that has been displaced by
b-o
from most of its range but has held on in the Wet Tropics rainforest. Perhaps
lurida
is related to novaeseelandiae and leucopsis, but the morphological evidence for
this is not striking. I can’t think of another pair of birds like this in the
Wet Tropics or anywhere else in Australia.
These are hypotheses generated by morphological data
(plumages and measurements) to account for distributions of taxa in an
evolutionary
framework. They could be tested by molecular studies or field work or
potentially other ways, but they have not been. I stress that they are just
hypotheses and my data are fairly cursory.
Thanks to Murray Lord, Jeff Davies and Martin Cachard for
stimulating conversations on this topic.
Kev Lobotomi suggested that ‘grey’ fantails are a similar taxonomic
scenario to the Ninox complex with dark forms in NZ, Tas and NQ. I see some
similarities but I think they may be fundamentally different evolutionary
scenarios. I’ve not looked at specimens of fantails so I am just theorising.
The unusual thing about the Ninox owls is that the break
between the two groups is Bass Strait. The Tasmanian birds sit with the NZ
birds. The Tasmanian Grey Fantails (alisteri) are darker than the mainland ones
(albiscapa) with slightly darker tails, but the differences are not huge. The
New Zealand Fantail (fuliginosa) is very different to alisteri and albiscapa.
Fuliginosa
has a black morph (which is virtually all black) and a so-called pied morph.
The pied morph is very orange below and warm brown above with all but the
central
pair of tail feathers almost entirely white; the juveniles are extensively
scaled rufous; the tail looks in the field to be bigger and is fanned even more
than in Aus birds, if that is possible. (Be nice to know if measurements
support the bigger tail, but I don’t have that vol of HANZAB).
Thus the break between the two groups of fantails seems to
be the Tasman Sea rather than Bass Strait. This means that a double invasion
scenario is not necessary. The simplest hypothesis is that ancestors of
fuliginosa
crossed the Tasman Sea from Australia to colonise NZ sometime in the last X
million
years (not too far back). Much more recently (<20 thousand years), the
formation of Bass Strait created a gap in the range of Grey Fantails in
Australia and alisteri and albiscapa began to diverge. The sea barrier means
that their breeding ranges do not abut so there is no longer any significant
hybridisation
between them. How long this needs to go on for until they become different
species
is a difficult question (how long is a piece of string?) Alisteri is not a
remnant but part of a diverging pair. By contrast I think that Ninox n.
leucopsis
is a remnant in Tasmania.
The form of Grey Fantail in the Wet Tropics (keasti) is very
dark and quite distinctive. It is the only form of Grey Fantail that breeds in
NQ. Albiscapa occurs as a winter migrant but since it doesn’t breed in NQ there
is no chance of hybridisation. It may be that keasti has diverged into a
separate species from albiscapa (another question about string), or it may even
a remnant that evolved from a different origin to albiscapa. The Ninox owls in
NQ differ because the breeding range of one (boobook and/or ocellata)
completely encircles the breeding range of the other (lurida).
Like Kev, I look forward to feedback.
Cheers,
David James
Sydney
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