The Bermuda petrel (Pterodroma cahow) is a gadfly petrel. Commonly known in Bermuda as the cahow, a name derived from its eerie cries, this nocturnal ground-nesting seabird is the national bird of Bermuda, and a symbol of hope for nature conservation. For 330 years, it was thought to be extinct.The dramatic rediscovery in 1951 of eighteen nesting pairs made this a ""Lazarus species"", that is, a species found to be alive after having been considered extinct. This has inspired a book and two documentary films. A national programme to preserve the bird and restore the species has helped increase its numbers, but scientists are still working to enlarge its nesting habitat on the restored Nonsuch Island.