Dave
I reckon these things become self fulfilling prophesies - a few people claim
Tasmanian Thornbills at Peter Murrell in trip reports, then other people go
there expecting to see them and don't look as closely as they need to.
Understandable, particularly if you have already ticked Tasmanians at another
site.
The two species are just very difficult to tell apart. Personally I find the
rufous primary panel on Tasmanians to be the most useful character; certainly
more reliable than the alleged white underpants. I looked into their calls a
while ago (but haven't ever got around to writing anything up). With practice
you can distinguish them on calls but it is hard to describe the difference.
Tasmanians don't make the harsh grinding notes that Browns often do.
The confusion in several field guides doesn't help. The description of the
Tasmanian call in Pizzey duplicates another author's misquote of a nineteenth
century description of the call by Legge; Legge actually used those words to
describe the call of Brown Thornbills. And a photographic guide has gone
through several editions with what in my view are two photos of Tasmanian
Thornbills to illustrate the Tasmanian and Brown Thornbill species accounts.
It's no wonder people struggle! And yes I have pointed those mistakes out to
the relevant authors.
Murray
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