Reading the Hormones

Behavior can tell the giant panda team quite a bit about the pandas, but the behaviors they exhibit are only half the story. When it comes to predicting when Mei Xiang will give birth, or when she is in the final stages of a pseudopregnancy, scientists rely on a few different factors. They monitor her behavior—is she nest-building, has her appetite decreased, is she cradling her toys, has she undergone physical changes—and, perhaps most important, they measure the levels of estrogen and progesterone in her urine.

Keepers have been collecting daily samples of Mei Xiang’s urine and, once a week, send those samples to the Endocrinology Lab at the Smithsonian Conservation Biology Institute in Front Royal, Virginia. As Mei Xiang’s hormone levels start to fluctuate, suggesting that she is preparing to give birth or is at the end of a pseudopregnancy (giant pandas’ behavior and hormones mimic a pregnancy even if they are not pregnant), endocrinologists help keepers determine when they should begin 24-hour behavior watches, or determine that she is not pregnant.

Smithsonian Conservation Biology Institute scientist Janine Brown began monitoring Mei Xiang’s hormones before she went into estrus to predict when Mei Xiang was ovulating. That initial change in hormones is called the primary rise. Brown’s job doesn’t end there, however. “We continue to monitor the hormones to make absolutely certain that the trend continues the way we predicted,” she says. And although scientists can’t tell the difference between an actual pregnancy and a pseudopregnancy—in both, hormone levels rise and fall in the same way—they continue to look for patterns, particularly in progesterone levels.

Now, a few months after the artificial insemination, veterinarians are conducting ultrasounds on Mei Xiang to monitor possible changes in the panda’s reproductive tract, and to get her accustomed to the procedure.

The next critical juncture is the secondary hormone rise that occurs just before the embryo, which can float in the uterus anywhere between 50 and 150 days, begins to implant. During this phase, there’s a very significant rise in progesterone. “That phase is actually much more predictable and lasts between 40 and 50 days,” Brown says. In Mei Xiang, it generally averages 45 days. (The secondary hormone rise has not started for Mei Xiang this year yet.) At that point, scientists will step up their daily monitoring of progesterone to track when the hormone levels return to baseline—a change that signifies the breeding season is over. “If it comes down to baseline and you don’t see a cub, it means she wasn’t pregnant or she lost the pregnancy,” says Brown.

Panda hormone analyses first began at the San Diego Zoo in 1986, where scientists used hormone assays developed at the University of California, Davis. Today, the Smithsonian Conservation Biology Institute has the world’s largest lab that carries out hormone monitoring of wildlife species. It currently has data on hundreds of species and conducts analyses of urine, feces, blood, saliva and hair. “We work with zoos across the country and field biologists all around the world that collect samples for us to analyze,” says Brown.