I don' t think ethics has anything to do with the weapon of choice, but rather how the hunter chooses to use that weapon.

If you' re asking the question, " Is killing a game animal with a bow as humane as using a gun?" I think you could find tons of information. Archery equipment can be a very humane way to take animals if the hunter does his part.

A hunter could be just as unethical with a gun as with a bow and arrow.

Good luck on your research.