Adults-only tours have made American zoos an unlikely hit with Valentines. Richard Kelly Heft reports
Humans aren't the only ones to display their affection on Valentine's Day. The San Francisco zoo has turned the rituals of animal attraction into a 14 February date.

The adults-only tours - sometimes romantic, often explicit and occasionally scientific - are held annually for V-Day and sell out weeks in advance. At $30 each, including champagne and truffles (pounds 20), the idea has now been copied by dozens of other zoos across the country.

The park stumbled on the idea when Jane Tollini, keeper and guide, noticed the tender devotion of the Magellenic penguins. "They're the most romantic animals in the zoo," she says. "He'll spend all day making up a nest to impress her, she comes home and says, 'I hate it' and they start all over again."

Couples are taken around the park on the Zebra Train while being regaled with stories of the sexual proclivities of the animal world. Featured rituals include enduring romances, tender courtships, uncontrollable libidos, and countless tales of polygamy, bondage, pan-sexuality and self- gratification.

While it sounds racy, the tour leaves all to the imagination. "Animals don't have sex on cue," says Tollini, "but I explain everything graphically - that's why the tour is adults only."

Judy and Peter Colasanti of Petaluma, California, will be going along today. "We've been married nine years and things are a little dull," says Judy, who has surprised her husband with tickets to the tour. "I thought this would add a change of pace to the occasion."

So what animal insights can the Colasantis expect? According to Tollini, elephants possess an erratic four-foot appendage that's "like a heat-seeking missile with a mind of its own". But once the female is impregnated, gestation and lactation take the next four years. Not good news for frustrated partners.

At the other end of the spectrum is the lion, possibly the randiest mammal on earth. When females are on-heat, lion males have been known to mate as often as 50 times a day, often going 24-hours straight.

Sexual practices, it turns out, are strongly influenced by an animal's place in the food chain - predator or prey. Giraffes rub their necks together and whack each other with their horns in a battle of stamina to determine the dominant male. For antelopes it's love on the run. And rhinoceroses' courtship rituals - which include head-butting, groin sniffing and body slamming (a technical term, apparently) can last a month.

But the bashful behaviour of the bald eagle is perhaps the most instructive to Valentines. To woo, the male fetches large amounts of food (rats, snakes, fish) to prove his worthiness. He then sheepishly inches towards his mate, staring at his feet and hoping for a sign that she's ready to mate. Being considerably larger, it is the female who is in control - the male can only wait patiently and hope for a positive sign. What he wouldn't do for a box of chocolates and a dozen long-stem roses.