I've revised the report of the Port Fairy pelagic we did in early May (two
months ago). I was uncomfortable with the ID of a prion seen on the way out
recorded then as an Antarctic Prion. Photographs and head enlargements
provided by Rohan Clarke and one by Chris Lester I reckon confirm that the
bird was a Salvin's Prion. And since I was responsible for the report, I've
changed it accordingly! My call. The amended parts of the report and a
summary of the reasons for my ID is below. I'd be interested in what others
think. The photographs have been sent to those who normally receive the full
report. If anyone else would like to see them, please ask.
SUMMARY: Prions were abundant, four species including Salvin's were
recorded.
BIRDS: 28 species (29 taxa) of seabird observed beyond the river mouth.
SALVIN'S PRION: 1 offshore in a.m. Photos by RC & CL. See Note below.
ANTARCTIC PRION: 1 pelagic.
*Distinguishing this Salvin's from Antarctic Prion. In the field I noticed
that the bird had the characters I consider indicative of a Salvin's rather
than an Antarctic Prion. These were the huge amount of black on upper tail,
whole of undertail appearing dark and the collar less bold than typically
seen on Antarctic Prions in these waters. But at the time, the image on the
screen of Rohan Clarke's digital camera suggested that perhaps the bill wasn
't large enough so I adopted parsimony and listed it as the species more
regularly identified in May, Antarctic Prion. But it niggled, so Rohan
produced some good dorsal images and head enlargements and Chris Lester a
shot showing the undertail pattern. I now consider that it was indeed a
Salvin's Prion for the reasons given below.
The black on the upper tail was more extensive than that on a
Fairy Prion. It extended across the full width, i.e. including the outermost
rectrices, which are grey in Fairy Prion, and extended from the extreme tip
terminating in a straight line some 30-35 mm towards the base of the tail,
i.e. as broad as on a Fairy Prion. Whilst Antarctic Prions have considerably
more black at the tip of the upper tail than Slender-billed Prions,
typically they have less black than Salvin's Prions and always less than
Fairy Prions. I can find no evidence that they ever have as much as shown in
this bird.
The undertail appeared wholly dark. Examination of numerous
beach-washed specimens indicate that Antarctic Prions occurring in Victoria
have a black triangular pattern in which the base of the triangle is at the
tip of the tail and the apex at the centre towards the base of the tail.
Whilst some Salvin's Prions are somewhat similar they often have dark
barring at the outer edge of the undertail (note that this is also mentioned
under 'Recognition' in HANZAB). This makes the whole of the undertail appear
dark. Some Antarctic Prions can have a little barring but it is never as
intense as the most heavily marked Salvin's.
Whilst the extent and intensity of the collar is variable in
both species, I find that the collar in Antarctic Prion is usually more
extensive than that in Salvin's Prion (Enticott & Tipling also note this).
The collar on this bird was restricted to the side of the neck.
The bill size of Salvin's Prion is more robust being longer,
deeper and broader than Antarctic Prion and as the sides are bowed, not
straight or concave as in our Antarctic Prions, the overall bulk is much
larger. I find it reminiscent of a Kookaburra! Whilst perhaps not utterly
convincing, the rather large bill is visible in the photographs and the
bowed outline is clearly visible.
Mike Carter
30 Canadian Bay Road
Mt Eliza VIC 3930
Ph: (03) 9787 7136
Email:
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