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Since chicks no longer need them for copulation, the penis has vanished. Now females are in control of sex. Yes it's true. But it’s strictly for the birds. There are 9,000 bird species and 97 per cent of them are penis-less. This phenomenon has confused biologists. But now, two researchers believe they know why the penis disappeared: because females prefered it that way. Females have control over males without a penis," says Robert Montgomerie, professor of biology at Queen’s University in Kingston, Ontario. Montgomerie and James Briskie of Oxford University have spent some time comparing those who have with those who don't. "The penis evolved because males needed it to force copulation," says Montgomerie. Most birds reproduce through a "cloacal kiss". The male deposits sperm from his cloaca- an anus-like hole- to his partner’s. The transfer lasts seconds. Male cloacas are larger because the tissue around the opening is swollen with sperm. Once the female receives the sperm, she actively draws it up into storage tubules. There the sperm wait until she is ready to release eggs. Only then are the eggs fertilized. If the female decides she doesn't want the fertilized eggs she can still dump them.