The story so far:
John asked about the Origma seen in the Capertee Valley given its
supposed restriction to Hawksbury sandstone
I replied: The Capertee Valley is an "enclosed valley" with
exceptionally scenic (Hawksbury) sandstone cliffs around about 90% of
the valley. Rock Warblers are regularly seen near the escarpment with
Glen Davis a spot often visited by birdwatchers. A lady I know has a
house at the base of the cliffs and a pair nests each year in her
garage. Munghorn Gap, about 85km to the north, is the excepted northern
limit while they also occur at Badger Ground (north of Rylstone)
north-west of the Capertee Valley. For the distribution of NSW birds I
wholeheartedly recommend the book by Morris, McGill & Holmes (title not
at hand) put out by the NSW FOC (I think) which details range limits of
all NSW birds. I hope this satisfies your curiosity.
John thanks me and remarked that he wasn't aware that Hawksbury
Sandstone was so extensive.
Not knowing when to leave good enough alone I replied: If we were to be
geologically correct I'm fairly certain the "Hawksbury" sandstone does
not extend that far. Origma's, I think, occur on what is collectively
known as the Sydney Basin sandstones, which is a collection of
sandstones including Hawskbury Sandstone. Perhaps this is verging on
the pedantic but it means that your initial question was a perfectly
valid one.
John replies: I see. I had wondered, given the prevalence of sandstone
and its associated vegetation all up the East Australian coast, why the
Rock Warbler, which is
relatively common in suitable spots in the Sydney area, was so
restricted in
range. Your advice partly answers this, but only partly, I feel.
It is time to throw open this discussion. Any birders out there with a
better geological knowledge of the Sydney basin and the distribution of the
Origma than I?
David Geering
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