Neil Shelley kindly brought the frozen Prion to my home this morning. In the
hand, my initial ID from the photographs as a Slender-billed Prion was
immediately confirmed by the slender nature of the bill with concave sides,
no visible lamellae and black on undertail restricted to a narrow black line
down the centre. But we still got out two sets of callipers, numerous books
and papers and poured over them for well over an hour and compared the bill
shape to numerous published diagrams, all of which pointed unquestionably to
that conclusion. However, there was significant discrepancies between the
references regarding bill measurements. Neil and I agreed on the following
dimensions (mm) for his specimen, each of which are either slightly above or
towards the upper limit for this species but too small for Antarctic Prion
and are out of the ball-park for Salvin's Prion. the very fresh specimen
will be deposited at Museum Victoria, Melbourne.
Bill length: chord of exposed culmen from tip to feathers 28.5, to skull 35.
Bill depth: at point level with base of culmen, 11.4 and at immediately at
front of nostrils 7.7, i.e. not at its shallowest point.
Bill width: at point level with base of culmen, 11.4.
It doesn't help when several sources don't advise or aren't clear as to how
or precisely where on the specimens their dimensions were measured. Some
were evidently made at a non-conventional point. For instance in HANZAB
Volume 1 bill depth for Prions is obviously at a point ahead of the nostrils
contrary to the instruction given on page 37. I'm sure such advice is there
somewhere but I couldn't find it. Also typo's such as that on page 540 under
'Recognition' for Slender-billed Prion, 'Bill measurements average 26.5 mm
long, 14 mm wide'! That 'average' is 1.5 mm larger than the widest reported
therein!
Mike Carter
30 Canadian Bay Road
Mount Eliza VIC 3930
Tel (03) 9787 7136
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