It took all of 15 minutes early in June for Sikhote and Sheba, Lincoln Park Zoo’s young, matrimonially inexperienced Siberian tiger couple, to get the hang of their conjugal rights and duties.
Since then, a roaring good romance has developed. Zoo officials this week said they will keep close tabs on the two tigers now that keepers are cautiously hopeful that Sheba may be in a family way.
Getting Sikhote and Sheba, representatives of one of the world’s most magnificent and endangered cat species, to mate was not exactly an exercise of doing what comes naturally. The tribulations of their meeting, courtship and love affair in fact demonstrate how little is known about an animal that has fascinated humans at least since caveman days.
Only 200 Siberian tigers are left in the wild northern forests of Russia and China. The 490 that live in 155 zoos around the world are closely monitored and very selectively paired off to avoid inbreeding and weakening the species.
Sikhote, Lincoln Park’s 7-year-old male, for instance, was never allowed to mate until experts found the ideal genetic mate for him.
She turned out to be Sheba, a 5-year-old who had never lived with any tiger except her mother, Adrienne, in Brookfield Zoo.
A stunning specimen with a lustrous, coppery coat, Sheba was easily the most desirable female Siberian in North America, at least by genetic standards.
That is because she was fathered by Zhivago, a tiger sent to Brookfield by the zoo in Leipzig, Germany, several years ago. Coming from Germany, he and his offspring represent a new pool of genes that eventually will broaden the genetic base of the captive Siberian tiger population in North America.
Last March the North American Siberian Tiger Species Survival Plan, a committee of zoologists who are sort of scientific matchmakers, decided Sheba should be moved to Lincoln Park to mate with Sikhote.
After Sheba was transferred to Lincoln Park, keepers there very gradually introduced the two animals.
Without seeing each other, they were first shuffled back and forth through enclosures so that they would become aware of and familiar with each other’s scent.
Later, they were allowed to view each other from afar for several weeks.
Eventually they were placed in adjoining enclosures with just a mesh barrier between them until they were comfortable in each other’s presence.
The arrangement was not entirely unnatural. In the wild, adult male and female Siberians live solitary lives, never socializing except in mating season.
“We were pretty sure Sheba would be in estrus (in heat) sometime in June,” said Alan Varsik, Lincoln Park’s mammal collection manager. “But before we allowed her to be with Sikhote, we wanted to be absolutely sure they were compatible.”
On June 4, Sheba was showing every sign of being a willing partner to romance. Keepers decided to let her and Sikhote finally meet without restraints in the indoor tiger enclosure at the zoo’s Kovler Lion House.
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Within 15 minutes Sheba was demonstrating to Sikhote her amorous intentions, Varsik said.
“She nuzzled his face under her chin, rubbed against his side, then crouched in front of him,” he said.
“Sikhote seemed confused as to what he was supposed to do. He tried at first to get on top of her head. But within a couple of minutes he settled down and figured out where he was supposed to be, and everything went fine after that.
“That first time,” Varsik said, “Sheba roared and turned and swatted at Sikhote’s face with her paw. But it couldn’t have been too unpleasant for her, because she went back to him repeatedly after that to solicit him.
“During that first day, she roared 18 times. The next day, I don’t know if they were tired or what, but they copulated five times.”
The third day, Sheba firmly let Sikhote know she was no longer in estrus, slapping him solidly across the face. After a few encounters like that, he got the idea, Varsik said.
Scientists are uncertain how often Siberian females go into estrus. In the wild, Varsik said, it may only be once a year. In zoo settings in warmer climates, they go into the mating cycle more often.
After Sheba and Sikhote’s June honeymoon, keepers began to carefully count the days, wondering if Sheba were pregnant.
It is difficult to determine visually whether a thickly coated tiger female is carrying a litter. There is no proven urine test for them. Keepers could try blood tests, but obtaining a blood sample from the animal requires first anesthetizing them, a procedure zoos try to avoid.
Knowing if a zoo tigress is about to give birth is crucial. In the wild, males have no part in rearing their young.
In fact, tiger mothers fiercely guard their young from any intrusion by adult males, who might kill the cubs.
“We let Sheba and Sikhote remain together through June and July, even though we weren’t sure if she was pregnant or not,” Varsik said.
“On July 29, she went into estrus again, and they mated through the first of August. We didn’t know if that meant she wasn’t pregnant, or if she was but that even pregnant tigresses can go into estrus.”
Varsik fired off faxes to tiger scholars at the species survival plan. It turns out nobody knows for certain. The experts told Varsik they believe Sheba was not impregnated in June but probably during her last bout of romance.
That would mean between 100 and 105 days from Aug. 1 (the normal gestation period), the zoo could have the most valued Siberian tiger cub litter in the country. Or, if the experts are wrong, and Sheba became pregnant in June, they could be here as soon as September.
“We’ll probably let them stay together for a few more weeks,” Varsik said.
“If they begin mating again, we’ll have to wonder if Sheba is pregnant yet. To be safe, though, sometime early in September we’ll probably separate them.”
Until then, if roars continue coming from the tiger habitat, there’s a good chance it means the honeymoon isn’t over.