The story of the North American plains bison, commonly known as buffalo, is thought of as one of the greatest early successes of the conservation movement. At the close of the Civil War, tens of millions of bison roamed the plains of North America from the Arctic Circle to Northern Mexico. Some estimates have put the population at 60 million. By 1880, just 15 years later, the species was nearly extinct. The bison populations that exist in North America today can all trace their ancestry back to 100 individual wild-caught bison bred on five private ranches and at the New York Zoological Park. All of these bison were interbred with domestic cattle at some point in time. The only bison population that remained wild was the Yellowstone herd that numbered 25 individuals according to official counts in 1902.
This is a sad story, but it has a hopeful ending. In 2002, bison populations in North America had recovered to an estimated size of 500,000. This is a small fraction of the tens of millions that roamed the West a century and a half ago, but is much more stable than 125 individual animals. The threat of this iconic species disappearing from the Earth is now behind us.
In the past 30 years however, our understanding of genetics has advanced dramatically and with it, our understanding of what a species is has changed as well. Scientists once classified a species by its physical characteristics and the ability of individuals to breed and produce fertile offspring. Today, our improved understanding of DNA and genetics allows us to compare the genomes of species side-by-side and classify organisms much more precisely. This better understanding of genetics has made clear to us (among many other things) how the bottleneck in the bison population around the beginning of the 20th century has had lasting impacts on the species as its population worldwide has grown from a handful of animals to half a million.
Process of Restoring Bison Herds
Of the 500,000 bison in the world in 2002, only 4 percent were in herds managed for conservation. The rest were primarily in herds managed as livestock for their production of meat. These animals were routinely interbred with cattle for traits beneficial to meat production. Traits beneficial to meat production, including rapid growth of marbled muscle tissue and docility, would not be beneficial to wild bison. Even the 20,000 or so bison which are in herds managed for conservation have almost all been interbred with cattle at some point in time. For much of the 20th century, a large portion of the bison population was bred primarily for meat production. This meant that wild traits were bred out and desirable traits for domesticated animals were preferred.
Efforts to restore bison herds have been further complicated by the risk of spreading disease. The wild population that exists in Yellowstone National Park is fiercely protected both for its own benefit and because of ranchers concerns about wild bison spreading brucellosis to cattle. However, 30 of the 4,000 Yellowstone bison were released to a U.S. Department of Agriculture facility in Fort Collins in 2011 to begin a project to breed genetically pure Yellowstone bison for zoos and conservation groups. This facility uses state of the art technology to extract fertilized embryos from pure-bred bison, chemically wash them to prevent disease transmission and implant them in a surrogate mother bison who is not pure-bred. The first successful transplant occurred in October of 2011 and a pure-bred male calf was born in April 2012 at the Bronx Zoo in New York. This process will make it much easier for pure-bred bison calves to be raised in places distant from pure-bred bison herds.
While there are currently no wild herds of bison in Colorado, breeding programs like the one going on in Fort Collins and the ever-growing interest in restoring wild lands in the West to their natural state may bring them back to Colorado one day soon.
Pete Wadden is the field research educator at Walking Mountains Science Center. He is looking forward to a wild and slightly wet summer of collecting stream data with the Natural Resource Interns this summer.