60 Million Bison!!! Really?

The number of American Bison at the time of the American Revolution is often estimated to be 60,000,000 animals.

Perhaps "estimated" is not the most accurate word. Perhaps "echoed" or "repeated" is more accurate.

Is 60,000,000 American Bison even possible?

 

Background

North America was home to many kinds of mega-fauna before humans who were proficient at chipping stone points and starting fires showed up. In a relatively short period, giant sloth, mammoths/mastodons, giant armadillos, cave lions and so on were extinct.

Bison were mobile and had more rapid reproductive rates than the other mega-fauna and the forage that had been consumed by other species was now available for them to eat. The Native-Americans had limited success hunting them in the wide-open prairies where there was limited cover to conceal their stalk.

Maximum, historic range on left.

Core range, blown up. Note that this is "short-grass prairie" and west of the dry-line.

It is my opinion that although sprinklings of bison were reported in the area of the "historic range" that there were not large numbers of them and they were primarily restricted to islands of tall-grass prairie maintained by frequent burns by Native-Americans or started by lightning.

Bison are most vulnerable to Timber Wolves (their only real non-human predator) when they were calving. Like the Passenger Pigeon, they congregated in large groups when calving/nesting and super-saturated the local area. Wolves might pick off a few of them but most would survive.

It seems probable that early estimates of bison populations were made as white Americans stumbled across these dense herds in May/June and they extrapolated beyond "as far as the eye could see".

The US cow-herd

A first-order estimate of "How many bison?" can be made by looking at the cow-herd in the "Plains States" + Texas.

If the typical rolling-cow herd in the US is 33 million, and if 60% of that herd resides in the states listed, then we are looking at roughly 20 million animals.

Those animals, especially the ones in the eastern-most portions of the Plains States and those in feed-lots get a lot of calories from corn that was raised with the help of nitrogen fertilizer and (often) irrigation. The domestic cattle herd also gets "helped" with stored feed so winter losses are usually very small compared to what a free-range, wild herd would endure. So the standing biomass of that 20 million cattle probably represents an over-estimate of the standing biomass of wild bison the same land area would have supported.

A more reasonable estimate than the 60 million mindlessly repeated as a fact, an estimate of 10-to-15 million bison seems more defensible based on the typical productivity of the short-grass ecosystem.

"But, but, but....ERJ, you are completely ignoring the TALL-GRASS Prairie ecosystem!!!" you might challenge.

I have to admit that history is not my strongest subject, but the reports of massive concentrations of bison were reported when the railroads hit the dry-line, not east of the dry-line. White settlers did not have the technology to kill bison in massive numbers before rifles with metallic cartridges came into common use. Before that, the number of "mountain men" was microscopic and the common settler probably had a smooth-bore musket with a bore between 0.57" and 0.68". Looking at the dates when bison were expatriated in Indiana, Illinois, Iowa, Minnesota and so on and considering the technology of the settlers, it is hard to believe that they existed on the Tall-grass Prairies by the tens-of-millions and were wiped out by the settlers.

Bonus link:

Standing biomass of wild mammals

Spoiler alert: Swimming biomass of marine mammals exceeds standing biomass of wild land mammals.

The species with the largest standing biomass is the North American Whitetail Deer

The species of mammal with the largest standing biomass are are humans followed by domestic cattle (two species).

Top nine wild land mammal species ranked by biomass