How Does a Female Porcupine Select a Mate? Carefully, Very Carefully
For porcupines, finding a mate poses unique challenges
In the dead of a dark Nevada night, Rick Sweitzer is thrashing through dense, high-desert brush in search of answers. The biologist from the University of California, Davis, is passionate about his work and on this night, he is particularly intent on solving a mystery involving the object of his passion: the nocturnal porcupine.
Of all the habits of these difficult to study creatures, none is more elusive and tougher to spy on than their mating behavior. "They are naturally shy and tough to locate, but they´re even more skittish about being watched during their mating rituals," says Sweitzer.
Porcupines are arboreal creatures, and in the Nevada region, they live and mate in thick riparian vegetation in which it is impossible for researchers to move quietly. So although Sweitzer has come close to catching the creatures mating, he has had to settle for stumbling upon pairs that seem to be on the verge of reproduction--animals that provide only indirect hints about how porcupines find and pick mates. But these clues have been sufficient for Sweitzer, along with fellow researcher Joel Berger of the University of Nevada, Reno, to put forward a theory that has earned them some notoriety in the select circle of experts who study this creature.
Based on their five-year study, the researchers suggest that it may be not only the chemistry of love but also the size of the male and density of his quills that make the females of the species choose their mates. "That´s because when you examine males that win the right to mate, it becomes clear they tend to be older, larger animals," says Sweitzer. "It does seem that, well, size matters, at least to female porcupines."
Whether it is driven by sight or smell, porcupine reproduction is a rough and selective practice, notes the scientist. The female is sexually active for only about one month a year beginning in late August. She also is very choosy. She requires her mate to guard her in Herculean fashion against all other comers for as long as three days--a grueling marathon in which even a winning male may emerge quite scathed.
These fights occur because the preestrus female climbs a tree and vocalizes loudly, making a sound similar to that of a cat. This mating call attracts males, which then fight brutally with each other. "It´s not unusual to see a winning, mating male with a hundred or so quills of rival males´ tails stuck in his face," says Sweitzer.
After the battling has determined the winner, the female descends from her perch and mating takes place as she arches her tail up out of the way. "She controls the situation," says Sweitzer. "So one way she might select her mate is by visually assessing male vigor or quality based on quill size or density."
Adult porcupines can be covered with about 25,000 quills, which vary in size on different parts of their bodies. "Large quills and more of them make porkies look big and healthy," notes the scientist.
Not all porcupine experts, however, believe that visual cues play as important a role as Sweitzer is ascribing to them. "While they may play some part," says biologist Uldis Roze of Queens College in New York, who has studied the animals extensively over the years, "I believe the predominant cues for mating selection by the female are still chemical."
No matter what motivates mating, one thing is certain: If the female does not want a particular male to mate with her, she will not move her quilled tail to allow her partner access. And those barbs are a definite no in any language.
"Rick and I are not as far apart in our thinking as some press reports might have you believe," notes Roze. "We both believe female porcupines cannot be raped. And this clearly implies that there is a female choice involved in the mating decision. She can choose among males, but the question does remain open as to the basis for her selection."
Roze notes that the animals mate at night and have poor eyesight. In addition, his own research into porcupine chemistry has shown, he says, "the animals have a rich variety of secretions that they use in their daily lives."
Both researchers agree that the issue is far from settled. Animal behavior, after all, is rarely a cut-and-dried affair. Although a porcupine´s eyesight is not particularly good, neither is its sense of smell. The most likely case, suggests Sweitzer, is that the female porcupine uses multiple cues for mate selection. As a result, the biggest and perhaps sexiest smelling males with large quills may fare the best in the mating game.
Writer Tom Dworetzky is based in Southern California.