Thinning the Herd

California’s Santa Catalina Island — also called simply Catalina — is located in the Pacific Ocean, about an hour’s ferry ride from the greater Los Angeles area. The roughly 75 square mile (194 km^2) island is home to about 4,000 people and is a popular tourist attraction, offering multiple resorts, parasailing, glass-bottomed boats, scuba diving and, perhaps surprisingly, a chance to see an American Bison. About 150 bison live on Catalina, and while they aren’t native to the area, they’ve become accustomed to their adopted habitat, thriving.

In fact, the bison like the area so much, they had to be given birth control.

The Catalina herd dates back to 1924. Fourteen bison were brought to the island during the filming of a silent movie called The Vanishing American, a western, thereby requiring the presence of western animals in a distinctly non-frontier area. (There’s some debate as to whether that’s why the bison are now on the island, as they don’t appear in the film, but the most common explanation is simply that the scenes with the bison didn’t make it into the final cut of the movie.) The producers intended to take the bison off the island after the shoot, but the movie was over-budget and the small herd was left behind, able to roam the island in search of food and, in a buffalo way, romance. Over the course of the next few decades, the Catalina herd grew to the hundreds, peaking at about 600 in the 1980s, according to NPR.

While the bison are generally well-liked and valued by the island’s inhabitants, they’re also unintentionally destructive to the native flora on the island, especially in large numbers. A Smithsonian profile of the bison herd explained: “The island, covering just 75 square miles, is home to more than 400 native plants, several of which are found nowhere else in the world. The free-roaming bison’s voracious appetite, sharp hooves, and penchant for scuffing out wallows—dusty depressions where the animals roll—took a toll on the grasslands. The bison and their shaggy coats also helped spread the seeds of non-native plants.” So members of the island’s nature conservatory took action, first selling off some of the herd (leading many bison to the slaughterhouse) and later relocating many of the bison to South Dakota, where their ancestors hailed from.

Unfortunately, shipping 1,000 pound animals over sea and land is both expensive for the people involved and less-than-ideal for the bison. In 2009, the conservatory took another crack at the problem. They rounded up the herd and injected the bison with a pig egg derivative called porcine zona pellucida, or PZP for short. PZP prevents the fertilization of the female’s eggs in most of cases, as the Los Angeles Times reports by causing irregularities in the reproductive cells. The PZP shots are very effective — it works in approximately 90% of cases — but it does fail, so there are still going to be a few more bison born each year due to the 10% or so of bison who are immune to what the conservatory calls a vaccine. But over the last few years, the number of newly born bison calves has dropped precipitously, as down to five in 2012 (per Smithsonian). The size of the herd has stabilized between 150 and 200 — the optimal size, according to the conservatory.

Bonus Fact: American Bison may look like glorious animals to watch, but don’t taunt them. Wikipedia explains: “Bison are among the most dangerous animals encountered by visitors to the various U.S. and Canadian national parks and will attack humans if provoked. They appear slow because of their lethargic movements but can easily outrun humans — bison have been observed running as fast as 40 miles per hour (64 km/h).”

From the ArchivesThe Longest One-World Sentence?: The word is “buffalo,” which is often used as a synonym for “bison” (but not in the case of the one-word sentence.

Related:  “Catalina A to Z: A Glossary Guide to California’s Island Jewel” by Pat Maxwell, Bob Rhein, and Jerry Roberts. Five stars on three reviews.