Female wild turkeys shopping for sex.
The determined males advertise themselves
to attract the females'custom.
Like all shoppers,
the females are keen judges of quality
and want only the fittest specimens to father their chicks.
As every male wants to be chosen above all others,
they put on their very best show.
By preferring some males more than others,
fastidious females have become agents
of evolution- moulding the appearance
and behaviour of their mates according
to what excites them.
Females are fussy for a good reason.
Throughout the animal kingdom,
they shoulder the burden of breeding-
this female hawksbill turtle is no exception.
While the male's contribution to his offspring
is a mere teaspoonful full of sperm- the female lays up
to five hundred yolk- filled eggs in a single season.
All females devote more time and energy to reproducing
than their partners.
Such inequality of investment makes females extremely choosy over
who fertilises their precious eggs.
Making eggs is physically draining-
it takes months to build up the reserves
to form these nutrient- rich packages.
As eggs are guarantees of future generations,
males use every trick to persuade females
to choose them as fathers.
lt's among birds that females exercise extreme power.
Some even force the males to prove their potential
usefulness through their courtship displays.
For instance, female royal terns set
the males a practical test.
They want a mate who's good at fishing.
He demonstrates this by courtship feeding.
A male that brings home surplus food supplements
the female's diet and helps her produce eggs.
These gifts are more than just a fish supper-
they provide vital information
about the male's hunting prowess.
Small offerings arouse no interest- anything less
than five centimetres is considered a worthless catch.
Equally, oversized gifts may indicate
an incompetent and inexperienced male.
Female terns need males that can reliably deliver
a regular supply of manageable fish.
Only when the male has proved himself,
is he allowed to proceed to the next step
of pair formation- mating.
Later in the breeding season the female will know
if her choice of sexual partner was a good one.
Now that there are hungry young mouths to feed,
the male's expertise at fishing is crucially important.
For several days,
the female stands guard over the chick,
and so she depends on her mate to feed them both.
ln the busy colony,
he locates his family by their calls.
ln these seabirds,
survival of the chicks is secured by the mother's initial choice
of an industrious male to help her.
ln some land birds, the females force the males
to demonstrate very different skils.
For weaver birds,
breeding success depends upon a strongly constructed nest.
Careful females only consider males
if they can prove their talent as master builders.
The first few strands are the most difficult to tie,
and must be firmly knotted
because they'll bear the weight of the completed nest.
Unpaired females carefully scrutinise
the work before making a decision.
At the beginning of the nesting season every male
is desperate to impress,
but some need more practice than others.
Once the foundation ring is finished,
the males are eager for the females to inspect their work.
Only top quality workmanship is rewarded-
it indicates a male can deliver a strong,
safe nest.
Once the male is chosen- he can carry on weaving
and complete the egg chamber.
When that is finished, the female lines the nest,
and lays the eggs.
Her wise choice of a safe home will provide security for the brood.
ln the jungle pools of Equador,
females are putting another group of males under pressure.
The quality of a male guppy is judged by his colour.
The pallid females have an eye for males
that are predominantly orange- a pigment accumulated
from their microscopic prey.
The intensity of the orange colouration is a measure
of their success at finding food- a talent that the females wish
to pass on to their offspring.
Flaming orange males are blatantly boasting
of their hunting skills.
lf a female is struck by a really colourful male,
she lets him approach and begin his courtship-
a zig- zag dance.
She's impressed- and pauses.
Brandishing a fin on his belly which forms a tube for mating,
the little male prepares to make the sexual connection.
ln a flash- the female is inseminated.
The pressure exerted by choosy females upon males
has resulted in some amazingly complex behaviours.
ln the rain forests of lrian Jaya,
male Vogel kop bowerbirds have been encouraged
to create colourful gardens.
Generations of hens have become connoisseurs of art,
bestowing their sexual favours only on the owners
of the most lavishly decorated courts.
Every season, males construct elaborate bowers.
These are highly decrated with all manner of natural treasures
which are displayed in the hope of gaining
the approval of a passing hen.
Some efforts are better than others.
For such dull males,
this kind of sexual advertising is better
than using colourful feathers.
Female taste can be instantly catered for
by selecting ever more attractive objects.
Unlike feathers these treasures can be rearranged.
Centre stage,
the mossy pillar is surrounded by a constantly evolving design.
By continually tinkering with is treasures,
the male hopes to find a winning layout.
Even beetle wing cases are turned over to reflect light-
and catch the female's eye.
Eventually, the critical hens fall
for the most creative male and his dazzling work of art.
But among birds, there are even choosier females.
ln Costa Rica, lives the most discerning of all.
Every female long- tailed manakin may select
from among eighty males,
and in the process drive them to exhaustion.
Males form dancing partnerships.
-this young green- backed male has teamed up
with a more mature one to learn the routine.
lt takes years of practice before the shows merit
even a passing glance.
But dancing is not enough- females also judge the males'
ability to sing together in tune...
...they utter four thousand calls a day.
Most males are failures.
Only one team in forty impresses the hens-
and only the senior partner gets to mate.
The winning team has taken ten years
of gruelling practice to get to the top.
By the end of the season the senior male has lost a quarter
of his body weight
-pushing him to the very razor's edge of survival.
Although exhausted, he's rewarded with sex.
On the wide open plains of Uganda,
female antelope have pressed males into forming assemblies
which act as mate markets.
This is one of them.
lt's a 'red-light district' for Uganda kob.
But here,
it's males who occupy their own plots,
and solicit for the custom of visiting females.
For most of the time the sexes live apart-
the females roam widely in the bush- but twice yearly,
the males gather on traditional mating grounds.
So when the females come into season,
they know where to find a mate.
Here they can choose from dozens of males.
Although the bucks all look equally impressive,
some have better 'addresses' than others.
The best is central,
and this is where all the females head for.
As every buck aspires to occupy this hot spot,
whoever holds it is constantly challenged.
A stud male may only have the stamina
to defend the central position for a few days.
Eventually, a more virile buck will topple him
and take over his desirable 'address'.
This time he successfully sees off his pushy neighbour.
For female kob,
the secret of the male's sex appeal lies not so much
in his looks as in the irresistible smell
of his patch of ground.
The pungent perfume is due to urine left
by a string of previous female visitors-
the sign of a popular male.
The latest female adds her own odoriferous
cocktail full of sex hormones.
The top buck savours it by passing it over a sensitive area
in the roof of his mouth- it's called the Jacobsen's Organ.
Having been chosen from among many males,
he gently takes the courtship a step further...
and with her consent he inseminates her in a second.
Such conspicuous sexual gatherings are not
without their disadvantages.
ln the dense foliage of a Greek orange grove,
males advertise at their peril.
These tiny suitors are Mediterranean fruit flies-
the females are pests that inject their eggs
into citrus fruit-
and the developing larvae destroy them.
Gathered in full view on the leaves,
each male produces a droplet of scent from his rear.
This is an aphrodisiac to lure the females in.
Broadcasting with their bottoms, the males signal their availability
and their cxact position in the dense foliage.
This aerial scent trail can be detected several hundred
metres away and quickly attracts customers.
The arrival of the female causes an outbreak
of vigorous wing fanning as the males try
to waft a stream of perfume her way.
lf she likes what she 'smells', she approaches the source
and her presence sends the male into a frenzy.
Her staunch attendance to his performance signals
that he may proceed to the sexual finale.
But such obtrusive behaviour has its dangers.
There are other customers on the wing!
Predatory wasps have learnt to home
in on the male fruit fly's ailuring scent.
Couples preoccupied with mating are easy prey.
The dismembered victims are taken back to the wasp's nest.
Beneath the waters of Lake Malawi male blue- banded cichlids
have solved the problems of advertising themselves
in a fairly featureless environment.
They've done this by landscaping.
On the flat sandy lake- bed the females head
for special sites where males compete
for their attention by building sandcastles.
Each of these mounds represents a stall
in their extensive mate market.
As females notice only those
with the most impressive properties,
the males are forced into a life of unremitting toil- each trying
to out- build his neighbours.
The choosy females have plenty of options-
there are up to fifty males here,
each trying to lure her into laying her eggs on his mound.
The female also needs proof that the mound is well guarded.
A robust male defends his sandcastle against other fish
that may disturb their courtship and steal the female's eggs.
Some mounds are clearly better than others.
ln open water, couples preoccupied with sex are vulnerable,
so to reduce the risks,
the business has to be conducted efficiently and quickly.
Only a well constructed mound will satisfy a breeding female-
this one's no good.
Once she's given her approval,
the male prepares to fertilise her eggs-
a job that involves a tricky manoeuvre...
...for the female is a mouth brooder.
After laying an egg, she snatches it back along
with a mouthful of the male's sperm.
Successful fertilization requires perfect synchronization.
For the female, this male is of no further use-
he'll go on building while she carrics her eggs safely
in her mouth until they hatch.
One of the ultimate expressions
of female choice can be found high above
the forest floor of Papua New Guinea.
Male Raggiana birds of paradise.
Everything about these ostentatious birds
has been fashioned by countless generations
of difficult- to- please hens.
Dawn breaks with their noisy clamour -so the dowdy females
can easily locate the groups of displaying males.
They visit one site after another,
judging each individual by his performance.
Their arrival causes a flurry of excitement.
At each site,
one male occupies a central position
which is more attractive to the hens.
lt takes seven years before the males mature
and acquire their ravishing plumes.
By contrast the hens are ready to mate much sooner-
and tend to outnumber the males.
Display perches are used year after year-
but only the most virile males hold the best position centre stage.
ln a forest so rich in fruit,
the females can rear their chicks alone-
the males are merely a colourful sperm bank.
Such independence means that the hens can shop around
for the most exciting males.
Each generation of females chooses just a few elite males...
...the majority are doomed never to breed.
This male is lucky,
but even now at the moment of mating,
he cannot be absolutely sure
that he'll father the female's next brood.
There's still time for deception as the sexual conflict enters
a new battle- the battle for conception.