Male cheetahs turn females on—literally.

That's because a specific bark triggers the female reproductive system to release eggs, researchers have found.

Unlike other cat species, female cheetahs ovulate rarely and at unusual times. They also lack a regular reproductive cycle.

But now, scientists know why—and the discovery may boost efforts to breed the rare cats.

A team of bioacoustics experts studying cheetah vocalizations stumbled onto the discovery.

They noticed that the male's "stutter bark" was made days before breeding took place, said research leader Matt Anderson at the San Diego Wild Animal Park.

Because calls unique to a single gender are often associated with reproduction, Anderson and his colleagues took a closer look.

Heightened Hormones

The team introduced a sexually mature female cheetah to two males during a series of experiments, recording calls made by the cats and monitoring the hormones found in their feces. (Hear the bark below.)

They discovered that male stutter-bark calls triggered increases in the reproductive hormones estrogen and progesterone in the females' feces.By recording and analyzing stutter-bark rates, the researchers showed that increases in stutter-barking steadily raised the female reproductive hormones responsible for ovulation.

"We never expected to see such a tight link between the vocalization and the hormone levels," Anderson said of the research, which has not yet been published in a journal.

"This came a real surprise."

Conservation Boost

The finding has big implications for breeding the rare cat, the researchers said.

The cheetah has an estimated adult population of only 7,500, according to the International Union for Conservation of Nature (IUCN).

The only known wild cheetah population outside of Africa today is a critically endangered group of fewer than a hundred in Iran.

"I think this just goes to show that telephone sex evolved before telephones," said co-researcher Fred Berkovitch, an ecologist at the San Diego Wild Animal Park.

"By documenting how sound makes animals horny, we hope to improve conservation-breeding programs."

Booty Call of the Wild

Using sound to jump-start reproduction is common among birds, but in mammals it is almost unheard of, experts say.

Male red deer are known to roar to advance the timing of ovulation in females, for instance.

But a male mammal using a signal to activate a reproductive cycle in a female has never been observed before.

Dan Blumstein, an ecologist at the University of California, Los Angeles, said the findings were "neat, but not unexpected."