Disappearing Bison

Do you ever feel like the blind men in the fable that were studying the elephant? You can grab the tail and say, “Oh, the elephant is like a rope,” and then grab the trunk and say, “Oh, the elephant is like a snake.” The trouble is, you can study the tail and trunk closely for years without realizing that they also go together!

I had one of those moments recently when the implications of something I’ve known for years hit home. Bison were disappearing from Yellowstone in the early 1900s.

Here’s the timeline according to my sources: Reports from 1856, 1870, 1873, 1874 and 1875 state there were very few bison in the Yellowstone Park area (Ricketts, 2006). Bison virtually disappeared in 1883, probably due to an outbreak of Texas tick fever in the northern herd (Koucky, 1983). By 1892, visual estimates indicated there were 300 bison in Yellowstone National Park (Ricketts, 2006). This population declined to 23 animals by 1902 (Hedrik, 2009).

So we know that bison were disappearing, at the rate of almost 30 a year, from Yellowstone at the turn of the century. Granted, there was trouble with poaching, but the problem was turned around in 1902. In that year, Congress appropriated money to spend on the disappearing bison problem (Ricketts, 2006). Was the money spent on a lot of armed guards? Maybe, but the sources record a different Congressional action. Congress supplemented the Yellowstone herd with an equal number of animals purchased from independent bison ranchers in 1902. The purchased animals were interbred in a ranch setting. Some purchased animals and/or their descendants began to be introduced into Yellowstone Park beginning in 1915 (Hedrik, 2009). The last remnants of ranch management methods were phased out by 1957 (Ricketts, 2006).

The number of Yellowstone-origin animals seems not to have changed from 1901 to 1907 (Hedrik, 2009). Were they not reproducing? The Yellowstone-origin animals may have come from a very, very small original population. Can extreme inbreeding of a small number of animals cause reproductive problems?

It turns out the answer is yes. The Charles Goodnight herd was established with five calves wild-caught from the southern herd in the mid-1880s (after the northern herd tick fever epidemic). Goodnight wrote one of two seminal articles about crossing cattle and bison in 1914. In 1997, the Goodnight herd consisted of 36 animals “directly and exclusively” descended from Goodnight’s original herd of bison and hybrids. (Testing showed that their genetic make-up was over 99.99 percent bison.) They were donated to Texas State Parks and Wildlife. A healthy herd of park bison would normally double in size in five years if no animals were removed. Despite no removals, the old Goodnight herd was only able to increase by four bison over five years. In 2001, out of 18 cows, three didn’t conceive, 10 aborted, and four of the calves did not survive. Only one calf was produced. Half of the tested bulls had defective sperm. This problem was overcome in 2003 ... three new bison bulls from an unrelated herd were introduced (Hedrik, 2009).

The parallels between this story and events in Yellowstone a century before are striking. In 1902, there were only 23 Yellowstone-origin (northern) bison in the park. These were supplemented by three Texas bulls from the Goodnight (southern) herd and 18 Montana cows from the Pablo-Allard (northern) herd (Hedrik, 2009). By 1903, Yellowstone bison were steadily increasing (Ricketts, 2006). At first only the ranch herd grew, but once members of the ranch herd were released with the original park herd, both herds grew. In 1973, Meagher estimated that the ranch bison accounted for 60-70 percent of the ancestry of the Yellowstone population at that time (Hedrik, 2009).

Were the Yellowstone-origin bison unable to reproduce in 1902? Was the herd collapsing under the weight of inbreeding depression? Was there some disease or genetic flaw that had doomed them to extinction?

Everybody knows that Plains bison were saved from extinction in the late 1800s through the efforts of a handful of ranch families, although some people are now trying hard to re-write that story. It appears that the Yellowstone herd, famous for having never been reduced to captivity, never polluted by the foul touch of man, may have also been saved by some of those families in 1902. Would the Yellowstone bison herd have snuffed out like a candle without the three Goodnight bulls from an entirely different source herd? I guess that now we will never know.

– Hedrik, Philip W. 2009. Journal of Heredity. 100(4)411-420.

– Koucky, Rudolph W. 1983. The Buffalo Disaster of 1882. North Dakota History: Journal of the Northern Plains. 50(1):23-30.

– Kara Ricketts Communication. 2006. Bison Management Analysis prepared for the Montana Farm Bureau Federation. 28 pages.