It is home to the Calayan Rail, a flightless bird identified as a separate species in 2004.

---

The Calayan Rail is one of the 20 known extant flightless rails. It is small and dark brown, with a distinctive orange-red bill and legs, and utters loud, harsh calls. Its habitat seems to be restricted to forests on coralline limestone areas on Calayan and extends to a total of less than 100 km². Biologists estimate that there may be 200 pairs on the island.