I love the idea of animals as an early food source.
It creates a sort of minigame for the opening turns, when little else is happening.
For the sake of clarity, and to familiarize new players with the mechanic, I would mention it in the unit description.
i.e., Warrior: +25% City Defense, +50% vs. Animals, defeated animals provide food
Furthermore, I would add a message, similar to pillaging, to the combat log.
Instead of "Your Warrior has pillaged a Farm for 3

," it would read "Your Warrior has defeated a Panther for 3

."
(If you can somehow mention which city the food went to, even better.)
Now, my only worry is that giving Warriors such an ability, along with +50% vs. Animals, greatly reduces the value of Scouts.
Scouts have an extra movement point, true, but that makes no difference when traveling through Forests, Hills, Jungles - in other words, almost anywhere interesting.
Knowing that Warriors can hunt animals (at 3

, with the combat bonus), I would never build another Scout.
At a bare minimum, I think Scouts should also be able to hunt animals. (On defense, of course.)
Even then, I think Scouts would need a second ability to make them a worthwhile build, as compared to Warriors.
I recommend one or more of the following:
- free Mobility promotion (Scouts would always move faster than Warriors, in any terrain.)
- free Medic I promotion (Scouts would heal faster than Warriors in the wilderness.)
- increased combat bonus, to +200% vs. Animals (Scouts would be just as strong as Warriors when facing animals.)