Choice D is the best answer. In (lines 70-74"surprising...for"), the author explains that glid-ing animals do not use a "flapping flight stroke," or WAIR, wing-assisted incline running. Since Chukars, a ground bird, use WAIR to help scale steep inclines, it can be reasonably inferred that gliding animals do not use WAIR to aid in climbing slopes.
Choices A, B, and C are incorrect because the passage does not include information on gliding animals' offspring, their method of locomotion, or their feeding habits.