Pulau Mantanani consists of three islands namely Pulau Mantanani Besar, Pulau Mantanani Kecil and Pulau Lungisan, a small island just off the western shore of Pulau Mantanani Besar. Pulau Mantanani Besar is about 3 km across and 1.5 km at its widest point. The island is surrounded by sandy, calcareous beaches, except on its northern side. Pulau Mantanani Kecil is a thin island 2.5 km by 0.7 km. The island is composed mostly of limestone bluffs and rocky shores, with little strand or kerangas vegetation (Sheldon, 1983). Pulau Lungisan is a 40 m high limestone stack covered with low trees and steep slopes close to Pulau Mantanani Besar (Møller, 2002).
The islands are important to pelagic species, wintering migrants and residents although the diversity is not great (28 species). Pelagic species such as the Frigatebirds (Christmas Island, Great and Lesser) have been recorded roosting in great numbers on Pulau Mantanani Kecil and Pulau Lungisan, one of the very few localities in Sabah where these migratory species can be found. These islands are estimated to hold 2,000-3,000 Frigatebirds Fregata spp. during peak season, with mostly juveniles and sub-adults (Møller, 2002).Other Near Threatened species that has been recorded are the endemic Mantanani Scops-owl Otus mantananensis, Malaysian Plover Charadrius peronii, Nicobar Pigeon Caloenas nicobarica and Blue-naped Parrot Tanygnathus lucionensis (Boden Kloss, 1930; Møller, 2002; Sheldon, 1983; Smythies, 1981). The Megapode Megapodius freycinet was found breeding on Pulau Mantanani Besar in March 1982, where eight birds and six active nest mounds were examined (Sheldon, 1983).
Non-bird biodiversity: (I) Globally threatened mammals (IUCN, 2002): VULNERABLE: Dugong Dugong dugon (Elliott, 2003).(II) Globally threatened reptiles (IUCN, 2002): CRITICAL: Hawksbill Turtle Eretmochelys imbricata; ENDANGERED: Green Turtle Chelonia mydas(III) Globally threatened plants (IUCN, 2002): No information.
BirdLife International (2019) Important Bird Areas factsheet: Mantanani islands. Downloaded from http://www.birdlife.org on 20/07/2019.