Masculine. If you don't know the gender of a noun, you can tell (in nominative, at least) by the gender of the article that's placed in front of it. We use ο for masculine, η for feminine and το for neuter.
Question: How can I be more general? How can I say "Eagles drink water."? Not the eagle or an eagle. Things like, Horses eat grass, cats eat mice, cannibals eat people.