Boatswain Bird Island covers an area of 5.3 hectares and fortunately has always remained rat- and cat-free. The Ascension frigatebird, along with a species of petrel and several species of terns and boobies, are believed to have bred on the main island until the arrival of humans and the rats and cats that they brought with them. These caused huge declines in seabird populations, limiting most of them to a few small colonies offshore on islets such as Boatswain Bird Island. However, the Ascension Seabird Restoration Project has been successful in eradicating feral cats from the main island and this has resulted in the return of seven out of 11 of the seabird species, including the frigatebird, the first two pairs of which were discovered nesting on the mainland in 2012. The most recent census in 2014/15 has found 44 nesting attempts on the mainland.