I would say a natural disaster like a forest fire that could kill trees that are their homes. A forest fire could kill the trees and also the cones they eat for food and thus destroy their habitat and also a source of food and the branches they use to travel from one tree to another in the upper stories of the forest.
After looking at the map/picture you have given above. There are several reasons why location D has a cooler climate than location E. Some of the reasons are a higher altitude, father north of the equator, location E is closer to the equator.
I know French is spoken in both Montreal and Quebec!
