Generally Germans make a difference between when people eat (essen) and when animals eat (fressen). By the way it also avoids the confusion of "unser Vogel ist" and "unser Vogel isst) :-)
I answered "Unser Vogel ist" and it was correct, but then I realize that my answer doesn't make reference to the action of the subject (eat). Thanks for the advice, is there any "rule" for something similar?
Yes. I notice that at the moment animals essen. maybe fressen comes later