Which change is most responsible for the decline of the kit fox population

Loss of : habitat & food cycle (prey)

Explanation:

Endangered species are the species which are facing risk of being extinct.

Kit Foxes have been in the list of federal endangered species in late 1960s, early 1970s.

The factors of their population decline have been:

Habitat Loss : Due to decline in shrub cover, as a result of reckless overgrazing Food Chain Mismanagement : Fall in their prey organisms' population.

Both these factors related to loss of habitat & food cycle (prey) have been most responsible for decline in kit fox population.