Kurtis,
Several thousand silver gulls roost and nest in the harbour (Cockatoo
Island, Goat Island, Snapper Island and under the Anzac bridge, I have also
heard they do the same at Homebush bay). I suspect they are foraging around
the lights for insects taking advantage of the light source on the bridge to
eat insects, you also see them active around the harbour foreshores at night
(i.e. on both ocasions not far from roost sites). The circling I would guess
is due to the fact that the light fades in a circular pattern around the
lights resulting in a concentration of insects close to the lights, they do
laps around whilst foraging (micro bats do similar).
If it was a courtship display i would ecpect that it would be a seasonal
occourence.
Cheers,
Ben
On Tue, Apr 20, 2010 at 5:07 PM, Kurtis Lindsay <>wrote:
> Hi all,
>
>
>
> For many years I have noticed large flocks (~100) of Silver Gulls flying
> high over the Sydney Harbour bridge at night.
>
> The birds seem to fly in loose flocks, and fly around in circles.
>
>
>
> I have always wondered about what might be the cause for this behaviour.
> Here are some of my theories:
>
>
>
> 1. The gulls are hunting insects attracted by the lights on the wing
> -
> has anyone seen gulls catch an insect on the wing before? Would there be
> enough insects up there to sustain such a large flock for such an extended
> period of time? If so is it the migratory Bogong moth they're attracted to?
>
>
>
> 2. The gulls are courting/mating - so loaded up with hormones the
> gulls continue courtship through the night, in the only place lit-up enough
> to do so ,under the bright lights of the bridge.
>
> At times birds are seen flying close to each other but there
> doesn't appear to be any obvious courtship. What does Silver Gull courtship
> involve?
>
>
>
> 3. The gulls are dazed and confused by the bright lights, and
> continue
> to fly around in circles. If this is so, why aren't there more
> dead/stressed
> seagulls found on the harbour bridge in the mornings?
>
>
>
> 4. The gulls choose to stay awake in a lit-up area as a predator
> avoidance technique, the bridge providing a safe haven and a clear flight
> path for a continuous safe flight throughout the night.
>
>
>
> Can anyone else shed light on this bizarre phenomenon?
>
>
>
> Kurtis
>
>
>
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