birding-aus

re Tricky Petrel Pairs

To:
Subject: re Tricky Petrel Pairs
From: "TPALLISE.AU.ORACLE.COM" <>
Date: 25 Sep 97 15:26:27 +1000
re: Westland and Black ID


To add my bit to David's Excellent message on difficult ID's.  In particular
the Westland Petrel vs Black Petrel problem. This has been a favorite subject
of mine ever since the 1996 NSW sightings.  I along with PH and others I have
been studying as many photographs as possible and looking at what specimens
are available for some time now.  The findings have been most interesting
albeit the sample range very small.

Putting aside the size, shape and bill colour (which DE has covered well) A
number of photographs that I have looked at do show some differences that MAY
be of use in the field when conditions are more than ideal. This has not been
tested widely and is only an opinion formed from the sightings of 3 WPs last
year and a handful of BPs and study of photographs. It would appear to me that
there is potentially a discernible variation in the bill length of both
species, even allowing for differing angles of the photos some bills do look
really short & deep and others look contrastingly long and slender.  What I am
trying to say here is that I have yet to see any Westand Petrel looking as
short-billed as some of the Black Petrel shots I have and likewise I have yet
to see any Black Petrels with really long bills like some of the Westland
shots.  On the other hand there are some that are very difficult to determine
with 100% certainty. One feature that did help in many photo's was the shape
and length of the maxillary unguis compared to the nostrils and this may help
in the field too. WP has a long maxillary unguis and often a more gradual
slope from the culminicorn to the tip of the maxillary unguis and certainly
two of the WPs seen in the field last year looked really long billed and very
deeply hooked. I think some of the reason for this was the longer maxillary
unguis.

Interestingly some of the photos of BP do hint towards the upper edge of the
latericorn with a more upturned quality than the WP photos and this is what I
am sure PH is getting at.  I think the problem here is that the sample range
it too small, we are only looking at one or two photos.  Recent visits to the
Australia Museum do not reflect these findings in fact if you take out the
size and bill length differences the WP specimens I looked at appeared almost
identical in structure and shape to BP, particularly the latericorn. Specimens
do show an extremely slight difference to the mandibular unguis length (WP
slightly longer and maybe more visible?) but this was so negligible I doubt if
it would be any use in the field even at close range.

No doubt we will learn more shortly as the procellaria season is upon us once
more.
ps: Have a look at the web site for some photo's of this excellent group
http://www.zip.com.au/~palliser




Good sea-birding
Tony
Phone.....+61 2 9900 1678 or Home +61 2 9427 7563
Fax.......+61 2 9900 1669


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