Transcript
David Attenborough: There's an Australian story about a
one-eyed man wandering through the desert who, before he stretches out on his
swag and goes to sleep, takes out his glass eye and puts it on a nearby tree
stump. But in the morning when he wakes, his eye has gone. Who can have taken
it? The bushwhacker, being wise to the ways of the wild, knows that there can
only be one explanation.
He walks off into the bush nearby, looks around and eventually finds an
extraordinary construction beside a nearby rock - two parallel walls of twigs a
couple of feet long and about a foot apart. At one end, there is a pile of white
objects, quartz pebbles, bits of bleached bone and some snail shells. And there,
in the middle of them, staring balefully up at him, his glass eye.
The thief, if that's what you want to call him, was a male bowerbird. And his
walls of twigs were not a nest, they were a kind of structure that is unique in
the animal kingdom, a sort of showcase - a bower.
A male bowerbird spends the bulk of his time working on it, either building
the walls or collecting fresh treasures to put in front of it. And all to
impress the females. They, at the beginning of the breeding season tour all the
bowers in the district. Every time a female appears nearby, the male goes into
paroxysms of strutting and shrieking, calling attention to his collection.
But the females are very choosy. If one is sufficiently impressed, she moves
into the bower and the two may mate there, or in some species flutter off
together into the nearby bush. Then away she goes, back to the nest that she has
built for herself and entirely by herself. There, unaided by him in any way, she
will rear her chicks.
He meanwhile continues doing what he can to add to his treasures and the
splendours of his bower. And hopes that his luck will continue. He's quite
pernickety. The bird that took the glass eye was probably a great bowerbird,
because that species prefers white objects. Other bowerbird species have other
tastes.
The satin bowerbird, which lives in somewhat better vegetated parts of
Eastern Australia, has a passion for blue. It's probably not a coincidence that
he himself has glossy blue plumage and a glittering blue eye. It's as though the
blue things he collects for his bower, blueberries, even bits of blue plastic if
he lives near human habitation, become extensions of his own body. Certainly
they seem to have the same effect as the extravagant plumes and decorations that
are developed each breeding season by birds such as pheasants, ducks and birds
of paradise. But in fact, his objects are rather more convenient than feathers,
because he doesn't have to grow them afresh every year. Nor does he have to
carry them around with him all the time.
On the other hand, no male bowerbird is happy to leave his bower for long. He
has competitors. If he is away, there's always the danger that one of his
neighbours will nip in and steal some of his painstakingly assembled treasures.
Worse, one might come and actually vandalise his bower, tearing down the twig
walls with his beak, so as to reduce the competition. Avenue shaped bowers are
not the only kind built by these amazing birds. Away to the north in the great
island of New Guinea, there are even more species than there are in Australia, a
dozen of them, and the bowers they build are perhaps even more extraordinary.
The first Europeans to see the constructions of MacGregor's bowerbird in the
thick, humid, tangled rainforest, could only imagine that it was the work of
local people, something to do perhaps with their bizarre rituals. It consists of
a sapling around which is constructed a tower of interwoven twigs that may be
four or five feet high. Around the base, even more remarkably, is a kind of
circular runway, the outer wall of which has a smooth rounded top made of
specially planted moss, decorated with little bits of evenly spaced black
fungus, like raisins. And there are treasures here too. They're not quite as
obviously attractive as the white pebbles or blue plastic of the Australian
species, but something more arcane that can only appeal to a really
sophisticated taste - frass, caterpillar droppings. He collects them from the
forest and attaches them to the ends of the twigs of his tower. When a female
comes by, he hides. If she alights on the wall of the runway, he will scuttle
round to the other side so that he's hidden behind the tower, and start to sing.
She cocks her head, listening, and he peeps out to see how she's reacting. If
she thinks well of it, she will hop down into the runway. That is a very good
sign indeed. And he whizzes round and executes an excited strutting dance before
the pair fly off into the bushes.
But even this maypole like tower is not the most elaborate of bowerbird
constructions. To find that, you have to go to the western end of New Guinea
known because of its shape on the map as the Vogelkopf, the bird's head. The
bower built by the Vogelkopf bowerbird is to my mind one of the most
extraordinary sights in all nature. Its core is a tower of twigs built around a
sapling like a maypole bower. But this is elaborated with a shallow thatched
roof stretching from the top of the maypole to the ground, so that it looks like
a low wigwam with an entrance on one side that can be a couple of feet across
and a foot high. The bower is so big in fact that you can almost crawl into it.
And that is not all.
In front of the entrance there's a meticulously tended lawn of green moss on
which the bird has carefully arranged his treasures - glowing red leaves, acorns
from a tropical oak, tree fern stems or iridescent beetle wing covers, each in
its own separate pile.
Not all the Vogelkopf bowers have the same kind of decoration. Some males
clearly prefer particular colours. A bush that has just come into flower may
provide a male with a speciality all of his own. Another bird may try to impress
with the collection of a particular fungus, and sometimes one so rare that he
has to bring it in from over a mile away. Watch the bird when he arrives with
his latest trophy, and you will see that he doesn't just dump it on its
appropriate pile. Not at all. He puts it down, hops back and looks at it
critically, cocking his head. And then maybe hops forward again, picks it up and
puts it back in a slightly different position. You have to think that he is
considering whether or not it is correctly placed from the point of view of its
overall decorative effect.
Each male it seems is trying to impress a female with his own special
arrangement. And the male that pleases her most will be the one she chooses to
be the father of her chicks. She reaches that decision by making an aesthetic
judgement, by choosing the display which pleases her most.
To film at a bower, you'll have to build a little hide a tactful distance
away. You must get into it before dawn so that the bird doesn't see you arrive.
And then you must wait. A male will almost certainly appear and start to
rearrange his treasures. Females making their tours of inspection are likely to
make only a cursory visit and then leave. But if your sequence is to be
complete, you'll need to end it with that last climactic shot in which a female
decides that this is the male for her. She makes that clear by flying down to
have a close look at the treasures on his lawn. Then the male, visibly thrilled
to ecstasy, rushes out of his wigwam, and the two mate, surrounded by his
jewels. Filming that is a different matter all together. To succeed, you
yourself will have to tour the bowers and make up your own mind as to which is
the most attractive. It's rather like going to a flower show and trying to
decide which entry is going to win the first prize. If you get it wrong, then
you may in fact sit in your hide forever and still not get that last shot. But
if you get it right, if you pick the one bower in perhaps a dozen in the forest
around you, then you will get that last crucial shot. The fact is that the
chances of you doing so are actually quite high. It seems that we and bowerbirds
have the same aesthetic sense and preferences. And that thought pleases me no
end.
http://www.abc.net.au/rn/scienceshow/stories/2010/2811707.htm
