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| Russet-tailed Thrush |
The
difficulty of distinguishing Bassian Thrush from Russet-tailed Thrush
in
the field has
led to a good deal of confusion about the respective distributional
ranges of these two very similar species, especially in areas where
they potentially overlap. Both
occur
in South-East Queensland, where considerable debate has taken place
about which species occurs where.
The
evidence suggests that Bassian Thrush in South-East Queensland is
primarily a bird of the higher
altitudes
(primarily in
rainforest)
of the Main Range and adjoining
Great
Dividing Range. The
species is resident across these ranges from Lamington
and Springbrook national parks in the south to the
Bunya
Mountains in
the north.
Russet-tailed Thrush occurs
generally at
lower altitudes; it is widespread and much
more
common than Bassian in
the
region. The
two species
occur
together in a relatively narrow altitudinal band in a small number of
sites
including
O'Reilly's Guest House in Lamington National Park and the Goomburra
section of Main Range National Park.
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| Bassian Thrush |
The
difficulty
of identifying the two species can not be under-estimated. I am among
many who have at
times made
the
wrong call,
corrected only when photographs were
scrutinised later. Some oft-mentioned features are
of little benefit with identification in
the field.
For instance, Russet-tailed has a little more white in the outer tail
feathers but this is very difficult to discern; the apparent absence
of white in the tail of
a bird is essentially meaningless. Russet-tailed has a more
rusty hue to the lower upperparts (evident in the first image on this post) with Bassian having a somewhat
more olive wash. This
feature however
is unreliable as
it is
difficult to nail
down,
especially with
the bird so
often being
in
poor light.
The
best identification features seem
to be
the more obvious buff tips to the wing coverts of Russet-tailed
Thrush, and the relatively narrow, longer bill of Russet-tailed.
However,
even these features are fraught, especially as juvenile Bassian
Thrush can show some
buff
edging to the wing coverts. Call is therefore of critical importance
to identifying these two thrushes; the
calls are highly distinctive and are
given
frequently.
In
the absence of definitive photographs, specimens or call recordings,
I had come to the conclusion that Bassian Thrush is
absent from those South-East Queensland mountain ranges which are
generally
lower than the Main Range and Great Dividing Range. I and
others,
for instance, have searched long and hard for Bassian Thrush without
success in the Conondale and Blackall ranges in
the Sunshine Coast hinterland.
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| Russet-tailed Thrush |
I
have camped often
in
plenty of sites at all altitudes in this area over the past 40 years
and have heard and seen only
Russet-tailed.
Chris
Corben, a highly regarded observer, was employed for several years by
the then state Forestry Department to undertake wildlife research in
the Conondale Range in the 1980s. Chris, one of the first birders to detect differences between the two taxa, was constantly on the
lookout for Bassian Thrush - his base high in the mountains was amid ideal habitat - but
he
also failed
to
encounter a single bird.
However,
it has
emerged
that Bassian Thrush is a rare visitor at least to the D'Aguilar Range
north
of Brisbane.
Judith Hoyle lives in the rainforest atop Mt Glorious, where the
altitude is similar to that of some sites where Bassian Thrush occurs regularly further
afield. Judith has heard Bassian Thrush on two occasions at Mt
Glorious. One bird was present for a week in
April 2014 in
the forest next to her home, its presence revealed by regular
calling in
the mornings and early evenings.
A second bird was
heard calling
in
March 2016
and on this occasion, Judith managed to record it. That call, which
Judith was kind enough to send to me,
is unmistakably that
of a
Bassian Thrush.
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| Bassian Thrush |
Judith noted that both Bassian Thrushes were exceptionally shy compared to the Russet-taileds which are common residents about her home. It seems that Bassian Thrush is a rare autumn visitor to the
mountain. Bassian
Thrush and Russet-tailed Thrush both
undergo
a degree of altitudinal migration, with some birds moving to lower
elevations
with the onset of cooler weather. It seems likely that the occasional
bird from the Main Range-Great Dividing Range population wanders to
other areas.
