Things are really happening on the Caloundra sandbanks at the moment. For a
start, birds are on the move, as total terns for the day were down to just
under 19,000. During the afternoon, about 25% of the flock was White-winged
Black Terns, 25% Littles, and 50% Commons. Only a handful of Cresteds,
Caspians and Gull-bills.
A change in the wind direction had terns arriving from the south instead of
east. We took up a different position for the evening survey, and it was
enlightening. When the evening flocks arrived, we were able to see them as
individual species instead of silhouettes, and I was staggered by the larger
proportion of White-winged terns (WWTE) around at the moment. The new
position worked against us once light really failed, and there was no shiny
sea surface against which to see terns arriving.
I'll stick my neck out and guess that we might have had close to 5000 WWTE
for the day. The highest number I have ever estimated prior to this is
around 2,500 WWTE. We were always unable to separate the evening terns into
species, as they flew in as silhouettes at distance.
At the moment WWTE are easily distinguishable from a distance on the wing
with their solid band of black underwing coverts. A small percentage, say
about 1-2% already show almost full black head, breast and belly, whilst the
larger proportion are in some stage of transition. A small proportion show
no sign whatever of changing from non-breeding plumage, and I guess that
these may well be first year birds.
That brings me to the next point. I have been much troubled by WWTE since
the spring. I will now mention this, in case there is someone reading this,
who has seen what I have seen.
When the WWTE first arrived from north in mid-October, they bore remnants of
breeding plumage, and that faded into non-breeding. A few weeks later, the
afternoon flocks had risen from the handful of starters to more than a
couple of thousand. What troubled me was that if the field guide & HANZAB
illustrations and text were correct, at that stage all of the birds I was
seeing were juvenile birds moving into first immature plumage. Their
upperwings were a dark, solid grey, which stood out clearly against the
other tern species. Their head black was broader than the usual adult
non-breeders. I really questioned my sanity, and read voraciously in every
publication. They all described the plumage I was seeing for several weeks
as first year birds, or else didn't cover the plumage I was seeing. I
couldn't accept that I had a flock of 100% first year birds in front of me,
week after week. Where were the adults? I had definitely had adults a few
weeks earlier. Then, by luck, an exhausted WWTE was brought into care up the
coast in Noosa, and another birder (Bob James) had already identified it as
a first year WWTE. I scooted up to Noosa for a look, and sure enough, this
bird, by now hale and hearty and eating its carer out of house and home, was
exactly the same as all the birds I was seeing on the Caloundra sandbanks.
And yet I was so wary of this conclusion, that I only ran it past a few
birders, who either dismissed me as crazy, or said it was unlikely. Except
for Chris Corben, who went to have a look at WWTE near him, and came back to
me with much the same tentative conclusion as I had made. I sat on the
information, and it ate at me.
Back to the present. The WWTE I am now seeing in non-breeding plumage are
pale, exactly as non-breeders should look, and bear no similarity to those
dark-winged birds of the early summer. I am now certain that if the
information in the literature is correct, I did indeed have a flock of 100%
young birds in early summer. As for the adults, I have no idea where they
went. However, throughout all of January we had only a handful of WWTE
present, the others gone to wherever. When they returned, there were no
Good, glad I got that off my chest. I conclude that WWTE separate into
age-based flocks. Whether it is a regular feature of their behaviour, or
whether this was unusual, is something I will learn in future years, when I
have accumulated more data. I remain fascinated.
Sunshine Coast, Qld
26º 51' 152º 56'
Ph (07) 5494 0994
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