"I'm not weighing human life against bison life; simply life to life."
You are contradicting yourself. You are comparing humans and bison as if they are equal in some way. Killing even one human is worse than killing any number of bison. But lets consider it on your terms, bison would still not top the list.
In that case it would be easy to argue that the extermination of the passenger pigeon was a far greater crime for two reasons: first we hunted them all the way to extinction and if the number of lives matters for some reason then secondly we killed somewhere around 5 billion of them, 100 times as many as bison.
Do you have any verifiable proof of that, or is it only because you are a member of the dominant species and that is the viewpoint of your species?
I agree that the Passenger pigeon should be first on the list, just above the bison.
your article noted that the bison didn't care when their families were shot down. People do.
This might help you make your list:
https://www.thoughtco.com/recently-extinct-animals-1092157
and there is this:
"According to the research, published today (Jan. 29) in the journal Nature Communications, cats kill between 1.4 billion and 3.7 billion birds and between 6.9 billion and 20.7 billion small mammals, such as meadow voles and chipmunks."
https://www.livescience.com/26670-cats-kill-billions-animals.html