The Antarctic terns were again at Cape du Couedic on Kangaroo Island today. In
a brisk southeasterly wind, they were located for most of the day (11am-4:30pm)
on Casuarina Island, about 300m offshore. From the boardwalk at Admiral Arch
using a scope, at about 40x zoom, the adults were easily found. They tend to
perch on the lowest rocks, along the lower edge of the line of white-fronted
terns, closest to the base of the rocks. All the terns (crested, white-fronted,
antarctic) were very mobile, regularly taking flight, dropping onto the sea and
often heading some distance offshore. On one occasion in the afternoon, I
observed a close fly-past by an Antarctic at the boardwalk, which afforded good
views of the tail (lacking black edge to outer feather), the uniformly plain
grey underwing, strong contrast between rump/tail and mantle, and grey belly
and throat. Viewed at full zoom (60x) most diagnostic features could be seen on
birds perched on Casuarina island: grey belly and !
throat, white cheeks, all red bill, red legs (relatively long compared to
Arctic tern). The bills also appear thicker-based than in arctic and flattened
laterally- more dagger-shaped than in arctic and reminiscent of bill-shape in
Caspian tern. Build-wise, the birds appear quite rotund, compact and less
attenuated than white-fronted (and Arctic). The tail streamers only just extend
beyond the wing-tips. The primaries are very slightly darker grey than the
mantle and contrast with broad pale tips to the secondaries.
The birds are in body-moult but the majority of the throat, chest and belly is
grey, contrasting with the white cheeks. The black caps are complete between
the nape and top of the head but almost the whole forehead is white.
To date, I understand the birds have tended to only perch near to the mainland
in relatively light winds / northerlies. What I found was the birds can be seen
and IDed offshore but only with a good scope. Even then, a patient vigil is
required to ensure you don't miss occasional fly-pasts, which reveal crucial
additional features.
Regards,
Simon Mustoe
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