Bob,
My reaction to your description is simple: if you're
really unsure of your identification, you haven't seen
a SIPO (South Island Pied Oystercatcher for the
uninitiated). Despite the obvious similarities, the
bird is really quite distinctive in a mixed flock of
(Australian) Pied Oystercatchers (OZPOs) and, with
careful observation, is easy enough to pick out.
Not all of your points are easy to answer. For
instance, your statement that "At least one standing
bird appeared to have shorter legs than the others,
i.e., the tibia appeared to be very short. However, I
believe this was possibly an illusion caused by the
way the bird was standing" is difficult to account
for. Why do you think it was illusory and how was the
bird standing?
>From what you describe you have not seen a SIPO, and
you certainly can't confirm one on the basis of your
description of the mixed flock you describe, given
that you didn't see your main suspect in flight. The
white wingbar extending to the trailing edge of the
wing is then diagnostic. However, while this generally
shows as a large panel when the birds are at rest, it
would be unreliable to base an identification solely
on this feature.
Of the two SIPOs I have seen (at Patchs Beach, south
of Ballina, and at Manly Boat Harbour, Brisbane) the
smaller body size has been readily apparent. So have
the short legs. The bird looks like a wind-up toy next
to typical OZPOs - it tends to scurry rather than walk
and its peculiar dimensions and horizontal stance
exaggerate this effect. The bill is certainly longer
(more importantly, it is also a different shape, being
not as deep as an OZPO) but you are, I think, right to
say that some OZPO bills are longer than others.
> A short distance to the north of this group there
> was a solitary PO.
> Being on its own I was not able to accurately gauge
> its relative size.
> I was able to observe the wing-bar on this bird; the
> wing-bar appeared to be longer than OZPO but was
> very narrow, about half the width of OZPO and SIPO.
> The white on the back appeared to be more extensive
> than for OZPO.
> The bird flew out of sight.
The length of the wingbar is not as important as the
breadth. It should be wide, clear, sharp and distinct,
and it must reach the trailing edge of the wing. An
isolated bird such as the one you describe would no
doubt be a more difficult proposition but shouldn't
prove too much of a hurdle when you know what you're
looking for.
In answer to your questions:
* The bird at Manly Boat Harbour has been photographed
and images were posted on Birding-Aus by Paul
Walbridge. Check the archives.
* This bird was identifiable on all of the appropriate
features, including leg length. As soon as you see a
"real" SIPO, you will be convinced about the
importance of this feature as well as relative size.
The difference is certainly subtle, but not so subtle
as you imply.
You obviously have all the right information at your
disposal so I won't labour identification further, but
in summary, the SIPO is safely and readily
distinguished on the above COMBINATION of features
(not just one or two).
Having said all that, it took me two attempts at the
Ballina site to finally see the bird, and I was
anguished at the prospect that I may actually have
overlooked it the first time. When I finally did catch
up with it, those fears dissolved - I recognised it as
being "different" instantly. I'm sure you will too.
Hope that helps.
AS
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