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| Finding Partners | | March
9, 2003. |  The
process of securing a mate in birds may be imperative but it should also be selective;
and it is usually the female who makes the selection. First she must assure herself
that a prospective partner belongs to the same species as herself. That is necessary
in order to avoid wasting time with a partner with whom she cannot have a fruitful
union. The question should be easy for her to resolve for a male has already gone
to some lengths to identify himself to his rivals and the signals he used for
them are likely to serve her equally well. If there is any possibility of confusion,
the males usually go out of their way to make the position clear.
The
blue-footed booby, which breeds on the Marietas islands in Banderas Bay, shares
some if its nesting sites with the yellow-footed booby. The two species are very
similar, except, as their names obviously imply, in the color of their feet. So
when a blue-footed male wishes to attract a female, he makes sure she knows who
he is by dancing, lifting up his ultramarine webbed feet with all the care and
exaggerated movement of a man wearing snow-shoes.
Once the possibility of confusion has been cleared out of the way, a female will
then need to satisfy herself that her partner is capable of giving her all the
help she needs to raise her chicks. A female European wren expects her mate to
provide her with a nest and a male may build up to a dozen nests in different
sites before he produces one that convinces a female that he will be an adequate
partner. Many females will require their mates to supply
food for them when they are sitting and for the young once they hatch. A male
tern starts his courtship by demonstrating his ability to do this by bringing
the female a gift of small fish, held cross-wise in his beak. He continues to
make such presentations long after he has been accepted as a partner and does
so immediately before each copulation. So while his initial offering might have
been a ceremonial proposal, subsequent ones become a valuable element in the female's
nutrition while she builds up the bodily reserves she needs to produce her eggs.
 Skills
in nest-building, fishing or hunting are obvious qualifications for a mate but
in many species, a female makes a rather more generalized assessment to assure
herself that the partner is in good health and likely to pass on his strength
and vigor to any offspring they may produce together. If he is one of those birds
that sings during courtship, the quality of his song will provide an indication
of his suitability. Singing, after all, takes a lot of energy. It also exposes
a bird to his enemies, something that could be fatal for individuals who are in
less than prime condition. Furthermore, a male who can afford to spend a lot of
his time singing is clearly either feeding in a notably effective way or the owner
of a particularly rich territory. In either case, he is a desirable partner.
She can also deduce his desirability from his plumage, using much the same criteria
as the male displays when establishing his rank among his rivals - the brilliance
of the bullfinch's scarlet breast, the size of the white patch on the forehead
of the collared flycatcher, the assurance of a blackbird's song and the glossiness
of his sleek black plumage setting off the intense yellow of his bill.
In those species where the sexes are similar or identical, the birds may select
their partners by dancing together. All species of cranes do so. They gather in
groups of a dozen or more and begin to bow and leap towards one another. They
flap their wings, bounce into the air and make sudden frantic runs. Sometimes
they will pick up a feather or a twig and throw it into the air as though it were
a toy.  Many
male birds sprout special plumes to adorn themselves for breeding. Male egrets
grow long white filigree feathers down their backs that they can erect in display.
As a result of these displays, male and females form pairs. Some birds find a
different partner each year; others, such as swans and albatross, mate for life.
Some pairs share tasks of nest-building and chick-rearing more or less equally;
others will split just as soon as incubation starts. There are polygamous males
and also females who take several male partners. But overall, some ninety percent
of birds species are monogamous. Some of the males in
that remaining ten percent are not only polygamous, but take no part whatsoever
in family life. Their relationship with their females is limited to the few seconds
that it takes to copulate with them. cupul@pvmirror.com Archives
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