English to French Science Environment & Ecology Animals in environment

I'm having problems translating the word "niche" in a text about birds and the evolution of flight. The word appears in 3 different sentences:

- "They can go very, very high, and they’ve taken advantage of this to fill all the different niches in the world."

- "These groups that have evolved the ability to fly and diversified into hundreds or thousands of species have gone on to fill in many different niches in the environment."

- "Flight allows birds to exploit niches that non-flying animals cannot exploit."

I think the word niche is a synonym for "aspect of the environment", that I could translate by aspect, caractéristique or particularité de l'environnement. Are these correct, and is there another, more specific, word that I could use?

Thanks.