NATURE On the prickles of a dilemma

The old joke is true. Porcupines do it carefully - select a mate, that is - according to a report today. Research has shown that female porcupines go for the biggest, spiniest males, which have to prove their worthiness by fighting their rivals.

Scientists from the University of California at Davis have been studying the creatures in Nevada for five years. They believe that impressing females may have been as important a driving force in the evolution of porcupine quills as self defence.

It is suggested that female porcupines may opt for males who are the best fighters.

The researchers found that the male guards the female for three days, waiting for her to become sexually receptive. During this time the female makes cat-like calls, apparently designed to invite competition from other males.

Fights inevitably follow, during which males bite each other and slap each other with their muscular tails encrusted with small, sharp quills.

Researcher Rick Sweitzer told New Scientist: "After a fight the loser can have anywhere between 30 to 50 quills stuck in his face and chest. It must be extremely painful." However, during sex the females were extremely cautious, and only rarely got spiked.