I was unsuccessful in a quick look for the Arctic Terns this afternoon
between 15.30 and 17.00. There were 130 Crested Terns on the large sand area
on the north side of the mouth of the Mordialloc Creek and 220 on the rock
platforms at Ricketts Point but no other terns. Don't yet know the time of
day originally seen but as that is often important I suggest others look at
other times and elsewhere. Since I got home, I've learnt that the first spot
described above is where James Bailey saw the birds and that it was on 2nd
not 3rd October. James is new to birding and not aware of whom he should
contact re interesting sightings. Nor apparently in the amount of detail or
precision desired in difficult confusion species.
Mat Gilfedder asked how often is this species seen in Port Phillip Bay. My
guess is about once every five years over the last 50 years. I would have
seen perhaps half-a-dozen but most were in the 1960's, 70's and 80's when I
was looking intensively at terns. One of those was at the Eastern Treatment
Plant, one was on Mud Islands and the others in the Sorrento/Portsea area.
Simon Mustoe asked why do I say that it is an Arctic Tern (the standing
bird). Firstly because it has very short legs, far too short for a Common,
White-fronted, Antarctic or Roseate Tern. Secondly, it has the dagger-like
bill of an Arctic Tern, shortish and evenly tapered from base to tip. Head
pattern is typical of the species in non-breeding plumage, i.e. tonsured or
monk-like with white extending to rear of crown, black restricted to side of
head and the nape. The six outer primaries are visible and are uniformly
dark indicating they are of similar age. No other confusion species would
show this in early October. Common would be closest with the four outers
being dark. On the far wing the black line on inner shaft of outermost
primary is narrow, about the same width as the shaft (wider in Common Tern).
On the near wing the black hook-back (where the black extends backwards
along the rear edge of the wing) on next-to-outermost primary is very
narrow. Would be much broader in Common Tern.
The flying bird is also an Arctic Tern but is in a different plumage and
from this dorsal view more difficult to ID. It is an adult that now has a
black instead of a red bill but otherwise retains much breeding plumage. A
ventral view would have made the identification of this bird easier but
again it has an Arctic's bill shape. The primary and secondary patterns are
the critical features. An adult Common Tern in October would have the four
outer primaries contrastingly blackish. On this bird they are all grey and
of similar age and wear. Otherwise I might have said that the extent of
black along the trailing edge could suggest that of a Common Tern if I
didn't know that the photo was taken in October and not May! The broad white
tips to the secondaries is very significant.
Mike Carter
30 Canadian Bay Road
Mount Eliza VIC 3930
Tel (03) 9787 7136
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