Answer:
i am not sure of this answer because there are a lot of answers for this question but what i came up to is that there might be a large population of different predators that hunts down this bird species
Explanation that means that the more the predator feeds on this bird species ( and other species too , unless this species is the predator's main source of food) the more the population of predators increase and that means that the predators will keep feeding on this bird species until it completely wipes out this bird species or the bird species migrates to an area where there are less predators.
(hope this help + i answered according to how i understood the question)
