Saturday, 22 October 2011

Opportunists of the Avian World

by Rosemary Penwarden

Seagulls, you would think, live and eat at sea, or at least beside it.
But a comment to my resident ornithologist about the small bunches of
black-backed gulls that have been flying inland over our house
recently, led to an explanation of what they were up to.

They were heading over to the rocky outcrops above Volco and the
reservoir above Sawyers Bay. Black-backed gulls nest in
October/November and so for the month or so before that they check out
the local prime real estate. The Volco outcrops are favourite; some
years Rabbit Island is popular, and 50 or so gulls often nest at
Evansdale. Black-backed gulls nest either in colonies or on their own.
Just like people, some prefer the urban throngs, others, solitude.
There is a big colony of a couple of hundred pairs at Merton at the
mouth of the Waikouaiti River. This year a couple of pairs have been
interested in the cliffs at Doctors' Point just past the caves. Inland
in Central Otago they nest on the braided rivers, up mountains, and
feed on the paddocks. There is a colony on top of Slopedown, the high
hill that overlooks the Southland plain to the west and the Catlins to
the east (the site of a soon-to-be-built wind farm owned by Meridian
Energy).

Pre nesting time, they also hang out with prospective mates, testing
for flakiness and finding out what they might get up to when their
backs are turned (in ornithological language it's called
re-establishing the pair bond).

Some black-backed gulls feed at sea on shoals of fish and squid,
others in marshes at low tide. There are those who roam the beaches
and pick up and drop clams, and others who feed in paddocks on worms
and dead lambs or whatever else is going. The real urban dwellers go
for the rubbish tips. Similar to human nutritional studies, it has
been shown that the chicks of these rubbish tip fast foodies are
thinner and more poorly feathered than their rural cousins. We have a
resident that flies ten metres above the Waitati stream each morning
looking for tasty little ducklings or eels. Unlike albatrosses, which
eat entirely at sea on squid, black-backed gulls can adapt to
anything. They are generalists, not too fussy about quality, as we saw
when they quickly discovered the oily burger patties spread along Mt
Maunganui beach a couple of weeks ago. They eat the eggs of terns and
smaller red-billed gulls. They attack oyster-catcher chicks. Round the
back of the Gardens New World once I watched in horror as one gulped
down a live sparrow chick that had been feeding on discarded
supermarket fare.

Once nesting has begun, chicks stay for a while in the nest – all
fluff and legs – but those in colonies move out, after a week or so,
into crèches. Black-backed gull chicks are awkward, sooty-brown and
smelly. They don't mind who feeds them and will have a go begging from
whoever comes near. Adults have to go and find their own chicks, and
there's the odd bit of playground bullying in the midst of it all. The
chicks fledge by about January. Young black-backed gulls look a bit
like spotty brown chooks. In their second year they start to look like
scruffy versions of adult gulls with teenage spots and a black end to
their tail. By the third year they are just like an adult, sleek white
with a black back, yellow beak and evil eye.

Our black-backed gulls are very similar to large seagulls worldwide.
This particular species occurs in Australia, South Africa, and South
America (circum Antarctica) as well as quite a few islands in between
like the Falklands. Elsewhere they are called kelp gulls.

They may be opportunists and their behaviour doesn't always endear
them to us, but black-backed gulls are a fascinating success story in
a world in which survival is becoming harder and harder.

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Ā ā Ē ē Ī ī Ō ō Ū ū
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