She's all come hither, but he's leery.

Could it have something to do with her swatting him after each encounter?

The much-anticipated mating of Kira and Dmitri, two Amur tigers at the Philadelphia Zoo, has yet to gell, and it may be the swat that is getting in the way.

When Kira first came into heat a month ago, the tigers mated time after time, for several days.

Keeper Tara Brody noted a slight weight gain in Kira, which raised everyone's hopes, but when Kira came into heat again just days ago, they knew she wasn't pregnant.

Now the endangered tigers have been at it again.

Yesterday, they mated 10 times or more.

As a frigid wind touseled the tops of bamboo trees in their exhibit, Kira flopped to her back in the snow, writhing and pawing the air.

Then she rose and trotted past Dmitri, glancing back.

He followed.

They rubbed faces.

Finally, she crouched on her stomach and Dmitri moved behind, grabbing the scruff of her neck with his teeth.

Hopefully, the keepers noted, this time it would work.

They want some cubs.

This time, at least the zoo staff didn't have to worry that the encounter would be fatal.

Unlike social lions, tigers are solitary, keeping company only long enough to mate. While Kira, the female, has already had three litters and is experienced in such matters, Dmitri was a novice.

Keepers were worried he would fail, become frustrated and, instead of ravishing her, attack. At 380 pounds to her 250, Dmitri could kill Kira in less than two minutes.

To the keepers' relief, it never happened. In heavily chaperoned sessions, with the veterinary staff on alert nearby in case of the worst, Kira and Dmitri mated seven or more times a day for several days.

Yesterday, as zoo staffers watched Dmitri and Kira try again, they wondered if Dmitri isn't quite finishing the job each time. Could it be the swat?

It turns out that it's central to tiger mating - indeed, to the mating of all cats, big and small - and it's something he'll just have to get over.

Part of the reason has to do with testosterone, which a female tiger is pumped full of when it's time for her to mate. That's so she can pick the fittest male and ward off the others, says Ron Tilson, who is director of conservation at the Minnesota Zoo and also coordinates tiger mating in North American zoos.

It also has to do with anatomy. The penis has tiny barbs - not sharp, but lots of them. The purpose is to stimulate the female to ovulate. Unlike humans, tigers ovulate only after copulation.

Tilson said the sensation of the barbs, for Kira, could be something like a hot poker.

Tilson figures it doesn't hurt her, or at least not too bad. But it's an electrifying experience that deserves a response.

"You can call it a love tap if you want," he said.

Older males learn to avoid the swat.

"I've seen male tigers do a standing high jump where their front and back paws are four feet off the ground," he said. "They go up like a pogo stick."

Tilson said Kira would go through more heat cycles, each of them intensifying, her estrogen building, until she becomes pregnant.

"There is a lot of growling and yelling going on during this," Tilson said. "They really get wound up. . . . You haven't seen anything yet."

See tiger videos, a blog, and more from the Phila. Zoo via http://go.philly.com/tigers EndText

Contact staff writer Sandy Bauers
at 215-854-5147 or sbauers@phillynews.com.