There's a long history of ambiguity about what is appropriate in a nature image. Audubon shot (with a gun) hundreds of birds to find good specimens. This seems to be a case where a trained animal was used to stage the photograph.
The ideal these days is that nature photos should show non-captive animals in the wild, doing things they do naturally.
Images of captive animals should be labeled as such.
There is some ambiguity about the ethics of baiting animals to get a good photograph, what constitutes baiting, and whether baiting in some cases (even when the bait is not in itself an unnatural part of the animal's diet) may be harmful to the animal by discouraging natural foraging patterns. I do some bird photography, and personally, I would never use bait to get a one-off shot, but I might take advantage of a well-maintained and monitored feeder at someplace like a National Wildlife Reserve.
There is an aesthetic preference among many nature photographers not to show the "hand of man" in a nature image, but this is something I question, since part of the story of nature to be documented in our time is the interface between the natural environment and human encroachment on that environment.