I watched Grizzly Man last night. Gracchi's review of the film is superb and there's not a lot I'd like to add to it. He gets to the core of the film with admirable clarity and perceptiveness. There's little sense repeating him except to confirm that this film is well worth watching.
All I'd add is that I found the footage of Timothy Treadwell (the Grizzly Man of the title) with the foxes more distinctive than either Gracchi or Werner Herzog (the filmmaker) did. The bears did seem totally uncaring with their only real reactions to Treadwell a hostility if he got too close and, finally, killing him when they were hungry. By contrast, I do think there was a genuine reaction from the foxes. They are animals with a social instinct that, as we do with dogs, humans can, I guess, become a part of. At times he did seem to have formed a connection with them more genuine than the one with the bears that were more central for the film and Treadwell himself.
I would guess that the foxes weren't enough because the relationship was more genuine. As Gracchi says Treadwell wasn't after an authentic, reciprocal relationship but something unreal. He found love that could not be requited safer. While the relationship with the fox was not real in the sense that human relationships are I still get the sense he preferred the complete fantasy of his relationship with the bears.