The sentence you provided is mostly correct but can be improved slightly for clarity and flow. Here's a corrected version:
"Instead of building their own nests, eagle-owls use tree hollows, gaps between rocks, and dips in the ground to keep their eggs and chicks safe."
Explanation:
- A comma is added after "gaps between rocks" because when listing three or more items, it's clearer to separate them with commas.
- Otherwise, the sentence is great and easy to understand!