I don't think they were endangered at the time. I think Roosevelt was acutely aware of man's impact on nature. Furthermore, I think Roosevelt was aware of the need to protect and preserve "the wild"

for example: "It is also vandalism wantonly to destroy or to permit the destruction of what is beautiful in nature, whether it be a cliff, a forest, or a species of mammal or bird. Here in the United States we turn our rivers and streams into sewers and dumping-grounds, we pollute the air, we destroy forests, and exterminate fishes, birds and mammals -- not to speak of vulgarizing charming landscapes with hideous advertisements. But at last it looks as if our people were awakening." [1]

I'd accept he liked killing, and the 10,000 animals is a fantastic indicator of that. I do think there's a bit more texture an nuance, given the time and technology. I'm not a fan of the "great man" model of history. I think a lot of his reforms would have come around anyway. But he really was an interesting character.

1. https://www.nps.gov/thro/learn/historyculture/theodore-roose...