SANTA CATALINA ISLAND, Calif. -- The hourlong ferry ride from Long Beach, Calif., to Santa Catalina Island is notoriously choppy. In 1924, a Hollywood film crew made the journey along with 14 special "extras" -- American bison.
The bison never actually appeared in the 1925 silent Western "The Vanishing American," and no one knows exactly why the burly Great Plains mammals became permanent residents. Some Catalina islanders believe the film's director, George B. Seitz, let the bison roam free thinking they would stick around the set. But instead they wandered off into the mountains where roughly 150 descendants remain nearly a century later.
While the rugged, semi-arid island is far from the bison's native prairie, the animals have thrived in the Southern California sunshine. The free-roaming herd grew to more than 500 animals by the 1980s, becoming a cultural icon and a celebrated part of the island's tourism-based economy.
Shops in the port town of Avalon sell bison stuffed animals, bison magnets and postcards with bison standing in the surf. Restaurants feature buffalo burgers and tacos (the meat is imported), and the local cocktail is called buffalo milk (bison are not technically buffalo, but the misnomer remains popular).
Along with enjoying the historic casino, kayaking and zip-lining, Catalina's estimated 1 million annual visitors can tour the "interior" of the island to catch a glimpse of the wild animals that were once on the brink of extinction.
"It's such a dichotomy -- buffalo standing in the surf," said Donna Harris, marketing director of the Catalina Island Chamber of Commerce. "It's one of the surprises that makes Catalina a little bit more mysterious, a little bit more quirky."
But the quirky 700- to 1,800-pound residents present the Catalina Island Conservancy, which manages most of the 48,000-acre island as a nature preserve, with a curious dilemma: How does the organization fulfill its charge to protect the delicate island ecosystem, including more than 50 plants and animals found no where else in the world, while managing what is arguably one of the world's largest invasive land mammals?
The answer to that question has changed over time.
At first, hundreds of bison were shipped to market, a strategy that upset conservancy supporters and some residents. Then, the conservancy relocated bison to a American Indian reservation in South Dakota, a more palatable solution to the public but not cost-effective: It costs about $1,000 to ship a bison. Biologists were also concerned about the potential to dilute pure restoration herds -- while Catalina bison are brucellosis free, they contain cattle genes.
From a purely ecological perspective, scientists say removing the bison would be the logical course of action. But there is no question, at least for now, that the beloved megafauna are here to stay.
"We look at our conservation mandate as a very complex balance of societal needs and ecological needs," said Carlos de la Rosa, the conservancy's chief of conservation and science.
To strike that balance, the conservancy has been working in recent years to stabilize the island's bison population at around 150, a number that can be naturally sustained by the island's nonnative grasses and coastal sage scrub. Managers appear to have found a humane, affordable method to maintain the herd size -- bison birth control.
Instead of 29 calves running around the island like last year, three bison babies have made an appearance this spring thanks to a vaccine known as porcine zona pellucida (PZP) that prevents egg fertilization. The initial dose was administered to female bison in November 2009 when the animals were already pregnant, so this is the first year managers have been able to evaluate the vaccine's effectiveness.
"It's working very well," said Julie King, the conservancy's senior wildlife biologist. "It's exciting to try something new as a scientist and see if it's an acceptable way to control the population."
PZP has been successfully used to control zoo bison and wild horse populations, but the Catalina Island program is believed to be the first application involving wild bison. King selected the vaccine over other hormone-based therapies because it does not change the bison's social behavior within the herd.
"Because the females are going into estrous, the males are still battling, jousting for those key females and going through those social things that they do," King said.
However, when the females do not get pregnant, they appear to go through multiple estrous cycles, so males also continue to rut. King is not sure how many cycles the females go through, but with no harsh winter on Catalina, the rut appears to last much longer than it does in the bison's native prairies.
This is one reason why PZP would not be a good solution to control bison herds at places like Yellowstone National Park, which has been seeking solutions to its own overpopulation problem. Males can lose up to 20 percent of their body weight during the rut, and if they don't switch their focus to fattening up to survive cold, snowy winters, they could die, experts say.
However, Rick Wallen, the bison biologist for Yellowstone National Park, said there are lessons to be learned from the Catalina Island program. "What are those changes in behavior that the population exhibits under contraception treatment?" Wallen said. "How much effort does it take to deliver a vaccine to the females?"
Given the difficulty of herding bison, which can run up to 30 miles per hour, King said the animals were lured into pens by a trail of hay bales and funneled into a "squeeze" normally used to brand cattle. There, they received identification ear tags, had blood drawn and the females were injected with the vaccine.
Every year, follow-up doses must be administered two to six weeks before the bison's estrous cycle for the vaccine to work. A much simpler and cheaper process, these doses are delivered in the field by dart gun for $26 each.
King said females were skittish right after giving birth and would run at the sight of a vehicle. "But as the calves got several weeks to a month old, you could literally drive into the middle of the herd, roll down the window ... and pop 10 or 12 out of each window," she said.
If the annual follow-up doses are not given, females can still get pregnant. This allows wildlife managers to select which bison should remain fertile to ensure adequate genetic mixing to sustain a healthy herd.
King said experts are still learning about the side effects of the birth control program. For example, she observed 2-year-old calves continuing to nurse because there are no newborns to compete with them, though she noted it is unlikely the mothers are still producing milk.
Occupying an island 22 miles southwest of Los Angeles has resulted in other physical and behavioral changes in the bison. They are smaller than their prairie counterparts by several hundred pounds. Mainland adult bison weigh between 1,000 and 2,000 pounds, making them the largest land mammals in North America. Catalina females, in contrast, weigh between 700 and 900 pounds, while males grow up to 1,800 pounds.
King said the animals' reduced size is partly related to the island's less ideal food source and all the extra exercise the bison get walking up and down island's steep hillsides. Adding credence to her theory is that offspring of the bison shipped to South Dakota grow to typical mainland size.
Catalina bison also live "a ridiculously long time" compared to bison on the mainland, King said. "We don't have predators [for bison]," she noted. "Our largest native mammal is a 5-pound fox. And there are no harsh winters, so we've had animals in their late 30s."
The absence of predators and a mild climate also change how female bison prepare to give birth. On the mainland, bisons' primary defense against wolf and grizzly bear predation is to stick together, so most calves are born amid the herd. Facing no such risks on Catalina, pregnant females find secluded spots to give birth and are not seen again until newborns are several days old.
"You could drive around the island and swear we have no bison," King said.
While island living appears good for the bison, it is not necessarily positive for the island's natural environment.
Bison obliterate native shrubs and cause erosion with their trails and wallows -- Jacuzzi-sized holes in the ground where bison roll around. Unlike on the prairie, the holes do not fill with water because there is so little rain and the dry bowls erode. And, while they help keep nonnative grasses under control through grazing, they also spread seeds of invasive plants on their fur.
Catalina, which is one of eight Channel Islands, is also home to more than 50 endemic species unique to the island, including a Catalina Island fox, mice, several birds, insects and plants, including an endangered mahogany.
"These are for us the crown jewels," said de la Rosa, the conservation director. "We are responsible for them not disappearing on our watch. If they are gone, they are gone from the planet."
However, the landscape is far from pristine. Nonnative grasses are widespread, and numerous imported plants have escaped residential gardens and now outcompete native plants in the favorable climate.
Managers must also deal with impacts from past land-uses that damaged the island's resources. For example, the land was once used for mining and grazing cattle and sheep. A sizable mule deer population, which was introduced when the island was envisioned as a game reserve, continues to cause significant vegetation damage.
While using science to guide ecosystem conservation and restoration, de la Rosa takes a decidedly practical and social approach. Instead of trying to restore the ecosystem to what it was before permanent human occupation, he said he plans to protect the species that are irreplaceable, while maintaining a functioning ecosystem that includes some nonnative species.
"It's not all or nothing," he said.
Conservancy scientists identified all the nonnative species and are working to remove the most damaging ones, such as tamarisk. They also have completely removed feral pigs and goats.
Bison also cause their fair share of damage, but social and economic values come into play, which are just as valid when it comes to conservation, de la Rosa said.
"Conservation is done for people, by people because of people," he said.
With the herd size under control, de la Rosa said the conservancy's next step is figuring out how to minimize the animals' impacts to the ecosystem while maximizing their visibility for visitors -- without corrals or too many fences.
"We're not going to put them in pens," de la Rosa said. "The whole attraction of bison here is that they are free-roaming."
Correction: A previous version of the story incorrectly stated the length of time the vaccine porcine zona pellucida lasts.