271 bird species have been observed in vicinity of Biebrza river. 181 from among them are hatching there.

There are 56 bird species in Poland considered as endangered or about to become extinct, 17 of them are nesting in National Park of Biebrza, among them: ruff, aquatic warbler, black tern, greater spotted eagle.

For some birds the marshes of Biebrza are one of the last places in Central Europe where they can find conditions to breed.