Hi Everyone,
There is little to report from the Caloundra sandbanks (SEQld) these days
which will stir your interest. The migrant terns have left, and the Crested
Terns are more abundant than in summer, without being remarkable. Gull
numbers are building up too.
We have noticed that as soon as the migrant terns leave, there is an
immediate change in the arrival behaviour of other terns and gulls.
In summer, gulls arrive in the evenings in a flight path which is closer to
the mainland than the Crested Terns, which in turn pass by more closely than
the large parties of migrant terns. Whilst it isn't set in stone, there
seems to be a general understanding about which airspace belongs to which
species.
Come last light, or about 15-20 mins after sunset, there is a lull in
arrivals, as migrant terns gather outside the breakers over the sea, form
larger parties, and then fly in along the entrance channel at a height of
only perhaps a metre above the water. The flocks can be up to a thousand
strong. Gulls and Crested Terns also fly in low, but not in the same tight
formation. During the summer we have few Crested Terns or gulls present,
compared with the vast numbers of migrant terns. The gulls will come in low,
but they don't wait for each other to form parties - they just stream in as
before, but at a lower elevation. We read dropping down as taking advantage
of light reflected on the water to find their way. This behaviour might
continue for another 20 mins, after which numbers are non-existent or
minute, and then we are unable to see anyway.
However, once the migrant terns leave, the skies are freer for those birds
arriving from the sea. We notice gulls and Crested Terns arriving over the
air space previously occupied by migrant terns.
A few weeks ago, Judy Caughley cried out, "Hey, look at this, these gulls
are behaving like terns!" Judy hadn't seen this before, as she has only been
in the team for about six months. But I was pleased that she had picked this
up independently of us, for it validated something we had noticed in
previous autumns. The gulls increase substantially in number immediately the
migrant terns depart, and may arrive in flocks of a hundred, two hundred,
more. Whereas they just fly in formlessly in summer, now as light
diminishes, they are gathering outside the breakers, winging like formation
flocks, until a considerable number is gathered, and entering as a group.
Whilst it's not earth-shattering, it's nonetheless interesting.
In an aside the the subject of this email, it interests me that whilst the
Caloundra sandbanks are a venue of choice by tens of thousands of migrant
terns in summer, there comes a point each year when all migrants terns are
gone from the sandbanks, and yet are present in small numbers in other
locations in the region. For instance, Judy Caughley reported on Friday
morning a hundred Common Terns, five Littles, and two White-winged Blacks in
the estuary of the Maroochy River (20km north of Caloundra). And yet when
we, including Judy, carried out our sandbanks survey that afternoon, we
found not one migrant tern. This behaviour has been the pattern for the full
three years of our project. Another instance of this is the intermittent
winter appearance of a handful of migrant terns at Buckley's Hole, Bribie
Island (30-35km south of Caloundra). One day we will work it out, but for
the time being we just speculate upon the reasons. You might say that they
will be immatures which will not migrate. This may be true in some cases in
the depths of winter, but there are also adults around on the shoulders of
winter. And why not in Caloundra? Food? Has the mobile kitchen moved on?
These questions are rhetorical, I know they can't be answered at this stage.
Cheers,
Jill
--
Jill Dening
Sunshine Coast, Qld
26º 51' 152º 56'
Ph (07) 5494 0994
Birding-Aus is on the Web at
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