My point in starting this thread was to encourage people to avoid trying to
use the absolute length of the middle toe of these two species or the
relative lengths of the middle toes of the two species as an identification
point to determine which species is being observed. The absolute lengths and
the relative lengths are irrelevant irrespective of whether the same method
or not was used to obtain the measurements used to compile the tables in
HANZAB.
Both species have elongated middle toes.
There is considerable overlap in the lengths of the middle toes of the two
species.
It is very difficult to determine the length of the middle toe when it is
wrapped around a tree branch. Even high quality digital images don’t make
that any easier.
Instead of comparing the middle toe lengths of the two species for
identification the toes should be used in the following manner:
- Estimate what percentage of the length of the middle toe is the length of
the outer toe;
- Note where the distal joint of the middle toe falls in relation to the
base of the claw of the outer toe.
The following percentages are taken from HANZAB:
For Brown Goshawk: outer toe c. 70% of length of middle toe;
For Collared Sparrowhawk: outer toe c. 63 – 67% of length of middle toe.
OK. When you have worked out how to accurately measure that in the field let
me know.
Also from HANZAB:
For Collared Sparrowhawk: distal joint of middle toe lies beyond base of
outer claw. (That is probably what makes the middle toe of that species look
particularly long but it could just mean that the outer toe is relatively
short compared to the middle toe.)
For Brown Goshawk: distal joint of middle toe is level with or shorter than
base of outer claw. (Perhaps the outer toe on this species is relatively
short.)
Once again, that could be hard to judge other than with the bird in the
hand, however, it is possible to see this in high quality digital images of
birds flying directly overhead.
Personally I would forget about using toe lengths as identification points
but would rather concentrate on the appearance of the bird/s. I am sure it
would be possible to eventually become proficient in evaluating the
appearance of the legs/feet (thick or thin, stout or slim) if one was to
observe enough examples of each species. Or if one was to take enough photos
of the two species of the quality of Chris Ross’s two superb images.
Bob Inglis
Sandstone Point
Qld
No Wi-Fi used in sending this email.
-----Original Message-----
From: Peter Shute
Sent: Friday, December 09, 2011 11:42 AM
To: 'Robert Inglis' ; 'Birding-Aus'
Subject: RE: [Birding-Aus] Goshawk vs Collared Sparrowhawk (middle toe
length)
I thought the important thing was the relative length of the middle and
outer toes. I think someone mentioned "length" in this thread without using
the word "relative", but I assumed that's what they meant. Is absolute
length important?
Peter Shute
-----Original Message-----
From:
On Behalf Of
Robert Inglis
Sent: Friday, 9 December 2011 11:47 AM
To: Birding-Aus
Subject: [Birding-Aus] Goshawk vs Collared Sparrowhawk
(middle toe length)
Question: Which has the longer middle toe - Brown Goshawk or
Collared Sparrowhawk?
edited here =
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