In 1979, Ballou and his adviser, Kathy Ralls, published a paper on the dangers of inbreeding—among them, a higher mortality rate. The paper pushed zoos to adopt a more responsible approach to wildlife reproduction. Ballou’s mean-kinship method gave zoos the tools to focus on conservation.
Think of zoos today as reserve banks, Steve Monfort says. If a species is threatened, animals from the captive population can reproduce and eventually be reintroduced into their natural habitats. In effect, zoos are an insurance policy against extinction.
“This model can only work if the captive population is genetically healthy,” says Budhan Pukazhenthi, a reproductive biologist at the National Zoo. If an inbred animal were to be reintroduced, it could bring genetic mutations into the wild population and hasten a species’s extinction.
The reserve-bank model depends on cooperation across zoos—that’s where the Species Survival Plan program comes in. SSPs are working groups of specialists and scientists from zoos around the country who monitor a species’s captive population. Most of the animals in SSPs have pedigrees—“We know the mom and dad for each,” says Pukazhenthi—and Ballou’s mean-kinship formula is used to identify breeding partners.
“It’s like eHarmony for animals,” says Monfort, who oversees the SSP for the Przewalski’s horse, the last remaining wild horse species. “It tells us, genetically speaking, this is the ideal mate for this animal.”
Only those animals most severely threatened in the wild are enrolled in SSPs. The Red List of Threatened Species—which is coordinated by the International Union for Conservation of Nature—helps zoos determine which species to focus on. The most recent Red List was published in October 2008. Of the 5,487 mammal species evaluated, 1,141 were deemed threatened—a 4-percent increase since 1996.
There are 113 SSPs managed in the United States, accounting for 10 percent of threatened species. Jon Ballou, who has overseen the SSP for golden lion tamarins for nearly two decades, says someone needs to sound the alarm before people will act. “We have examples of species that have gone into decline because nobody was paying attention,” he says. “Every species needs a champion.”
The passenger pigeon was championed too late. Once believed to be the most abundant bird in North America, it became extinct in the early 1900s due to habitat loss and over-hunting. The last known passenger pigeon, Martha, died at the Cincinnati Zoo in 1914.
Martha’s body was donated to the Smithsonian, where it was mounted and put in a display case. Next to it was a plaque with these words:
“Martha, last of her species, died at 1 pm, 1 September 1914, age 29, in the Cincinnati Zoological Garden. Extinct.”
It’s a cold spring morning in Front Royal, and Wynne Collins, a reproductive scientist at the research center, is doing her morning rounds. Her first stop: the Przewalski’s horses.
Three or four herds of mares graze in grassy pastures divided by a chainlink fence. Collins unhooks the latch and lets herself into the paddock. She’s greeted by the horses’ caretakers and a zoo volunteer, who are here for a training session in “the chutes,” a maze of stalls leading to a hydraulic lift that restrains the horses during reproductive exams.
The $30,000 machine is clunky and loud, but it’s the best way for Collins to do her work. Unlike domestic horses, Przewalski’s horses—P-horses for short—aren’t accustomed to human interaction. The stocky, stubborn animals stand about as tall as ponies.
The four mares from New Mexico are the most difficult. Referred to by numbers rather than their Chinese names—Collins never mastered the Chinese pronunciations—horses 11 through 14 have been at the research center for 16 months. Inside the chutes, they buck and charge at the doors. The wooden stalls shake.
Collins waits for number 11 to quiet down before sending her to the hydraulic lift. “Door,” she says softly, as if speaking to a toddler. The barrier slides open, and the horse surges forward. Another door shuts behind the mare, penning her into the machine. It whirs for a minute before 11 is released and sent galloping back to the paddock.
All this for a gynecological exam. During breeding season, Collins conducts regular exams to monitor the horses’ reproductive cycles, and for nearly five years she has collected urine samples to measure their hormones. As in humans, spikes and declines of certain hormones can signal pregnancy. Collins stores hundreds of vials of urine in a freezer in the lab.
Because P-horses’ mating was never studied closely in their natural habitat, scientists know little about reproduction within the species beyond what they’ve observed of the animals in captivity. It’s a limited sample set: All of the P-horses in the US captive population can be genetically traced to just 14 horses. Today there are about 1,500 P-horses in zoos around the world; the National Zoo holds 26.
Steve Monfort is a longtime champion of the species, which was close to extinction 40 years ago. In 1986, he founded the zoo’s endocrine-research lab, a workspace for scientists to study reproductive health and monitor hormones in wildlife species. Monfort’s first research subjects were P-horses.