[Sacajaweau]

There were 10 million ???????? Don’t believe it for a minute.

[Rockingham]

That many and more, with a range that in prehistory extended into the eastern US.

[Vaquero]

1 herd would cover what is now 2 or 3 states. General Sherman said if we kill the Indians food we get rid of the Indians.

[muir_redwoods]

I’ve read estimates of as many as 60 million on the North American continent at one time.

[Jeff Chandler]

Major Richard Irving Dodge:

“(The whole country) appeared one mass of buffaloes, moving slowly northward. Only when among them could it be ascertained that the apparently solid mass was an agglomeration of innumerable small herds of fifty to two hundred animals…(this herd) was about five days in passing a given point, or not less than fifty miles deep. From the top of Pawnee Rock I could see from six to ten miles in almost every direction. The whole space was covered with buffaloes, looking at a distance like one compact mass, the visual angle not permitting the ground to be seen.”

[piasa]

I believe it.
The continent looks much different today.

Then there were also flocks of passenger pigeons so large that they darkened the sky and when landing often broke the branches of roost trees. When their nestlings began fledging there was a big nutritional feast for predatory wildlife, and for people...
and when the breeding season was over, the area beneath the trees was covered in fertilizer, and subsequently grew excellent forage for deer, elk, and bison. There were enormous stands of beech nut trees and further east, chestnut trees.

There were also the plague of swarms of locusts in the West on the plains.

Much of the Eastern US was covered in vast stands of river cane rather than trees and it was excellent forage for grazers. One of these great stands was in Kentucky with a salt lick in it which drew herds of bison to it. In this salt lick were found loads of ancient bones showing the site had for thousands of years before had drawn giant ground sloths too, and mastodon.

And there were raucous flocks of colorful Carolina conures/ parakeets, a parrot that looked similar to Jenday Conures.