For millions of years, female elephants have managed to give birth successfully without being poked, prodded and worried over by humans.
But at the Maryland Zoo in Baltimore, keepers and veterinarians are posting a close and anxious watch over Felix, who is poised to deliver the first elephant ever born at the 132- year-old zoo.
Their 7,490-pound patient, whom they describe as "kinda petite," is due any day now. So her vets and handlers have stepped up their maternity preparations.
The pregnant pachyderm is submitting good-naturedly to blood tests - drawn daily from her ear as vets watch for the hormonal changes that signal an impending delivery. Ultrasound tests are repeated every other day to keep watch over Felix's already frisky calf and the dilation of the mother's cervix.
In the 10,000-square-foot elephant barn - spruced up with wood chips, a $1 million renovation and "calf-proofing" - keepers are on a sleepless, 24-hour watch over their princess. They're looking for any change in behavior that might signal that her time is nigh.
On average, five African elephants such as Felix, as well as three Asian elephants, are born in the United States each year, according to Mike Keele, deputy director of the Oregon Zoo in Portland and chairman of the Elephant Taxon Advisory Group at the Association of Zoos and Aquariums.
About a third of the Asian infants die in their first year of life - about the same as in the wild. Keele said he thinks infant mortality among African elephants in captivity is less than that.
But with experienced moms such as Felix, Keele said, "the risk goes way down. She should take care of the calf without any problems."
Such births, and the excitement they generate, increase the public's interest in efforts to help preserve elephants in the wild, he said. The fact that 10,000 people went to Baltimore's zoo for last weekend's opening day - many to see Felix, according to zoo officials - suggest that the impending birth is already having an impact.
On a smaller scale, elephant births are good for a zoo's revenues, and they're "really important to the mom and that herd," Keele said. The infant's presence helps strengthen the group's cohesion.
Felix seems unaffected by it all. She has been posing for photographers and zoo visitors, and ambling around the elephant pen in the late winter sunshine as if she had everything under control.
But no one at the Maryland Zoo wants to take chances.
Mike McClure, the zoo's general curator and elephant manager, traveled last year to Riddle's Elephant Sanctuary and Wildlife Center in Arkansas for training in the management of elephant births.
Riddle's is where Felix, 24, retired after a career in show business. She and Tuffy - a 23-year-old male - lived there until they were brought to Baltimore to expand and diversify the Maryland Zoo's herd.
McClure and Felix both were present at Riddle's to witness a delivery. "She was very interested in the other elephant's calf - smelling it, touching it and investigating," McClure reported.
Felix's first calf was born five years ago at Riddle. "She was a very doting mother," McClure said. That calf was a male. Zoo officials know the new calf's gender, but they aren't saying.
Tuffy isn't the father. He has never been mated, although zoo officials said they hope he and Felix might hook up once her next calf is four or five years old.
Felix was already 19 months pregnant when she arrived with Tuffy. Her belly bulges a bit in front of her left hind leg, and her mammary glands - just two, between her front legs - are visibly swollen.
Her prenatal care has intensified here since her arrival.
Since early February, said senior zoo veterinarian Dr. Ellen Bronson, Felix's keepers have drawn blood from a vein behind her huge ear. Two tubes are taken daily and tested for signs of infection, kidney and liver function and, most of all, hormone levels.
"For the last month, we've been looking at progesterone," Bronson said. The hormone, produced by the ovaries and placenta, is vital to maintain a pregnancy, and to promote mammary development.
"Two to seven days before delivery, it drops to baseline, as if she were not pregnant," Bronson said. That's the signal to the body to begin the delivery process. So far, there has been little change. "We're sitting on pins and needles watching those numbers," Bronson said.
Samples are being sent daily for confirmation at Johns Hopkins Hospital, and twice weekly to the National Zoo's Conservation Research Center in Front Royal, Va.
Felix is also trained to accept ultrasound exams, every other day. One is performed rectally to check her cervix, which will start to dilate 12 to 24 hours before delivery. "Right now she's all tightly closed," at about 2 centimeters, Bronson said. In time, it will open wide enough ... well, for an elephant to pass through.