Two species of warbler are very similar. However one forages in the top of the trees while the other forages near the bottom. Which explains this difference?

I would say this is niche partitioning.

Explanation:

Every organism has a certain range of requirements called a niche. The competitive exclusion principle states that two organisms cannot occupy the exact same niche without one out-competing the other. Niche partitioning is basically changing some aspects of a niche so that there is no need for competition.

where's the

if you are on the computer you can not take a picture but you can upload one but i am not sure about phones but i'm pretty sure it's the but to upload one just click the paper clip looking thing/ link thingy thing and upload a pic