Your sentence is almost perfect! Here's a slightly corrected and clearer version:
Seabirds eat fish, so most of the time they fly over the sea following schools of fish. They also spend time on land, where they come together in groups to find food and keep their little ones safe.
Explanation:
- Added a comma after "on land" to separate the clauses clearly.
- Everything else is correct and easy to understand!
Great job writing about seabirds!