Why are owls considered keystone predator

Explanation:

Keystone species are animals that help manage other animal species by controlling population numbers and biodiversity within an ecosystem. The impacts of keystone species are usually greater than their numbers. 

owls can be a great benefit to places where rodent populations are high. Dense urban areas often suffer from an abundance of rats and mice spreading disease, and rural agricultural communities have their crops consumed and soil eroded from burrowing voles and field mice. Without owls, and other top predators, rodent populations could explode and exacerbate the effects they produce.

the owl is a keystone species, as many other birds. and it gives them the nutrients they need when they eat the bird and it mangeges the population of the other species:)