Which is part of the niche of the american pikas?
a. they climb mountains.
b. they feed on dead organisms.
c. they build nests far out on tree limbs.
d. they find shelter between rock fragments.

American pikas find their shelter between rock fragments.

Option D

The "American Pika is a small" member belonging to the taxonomic order Lagomorpha, which includes rabbits and hares. These mammals are well-adapted to cold alpine climates which make them survive the toughest weather of the Colorado. The American Pikas can be found in isolated rocky areas at up to 3,000 meters in elevation.

They also have the ability to live in piles of broken rock. It is also believed they live in the "man-made substrate like mine tailings" and piles of scrap lumber.  Their den and nest are of 0.2–1 m in diameter which is find below rocks. Pikas habitats "near or above tree line".