The Polillo Island group lies about 25 km off the eastern coast of Luzon, and is composed of 24 scattered islands and islets, most of which are inhabited. The largest island is Polillo (76,100 ha), followed by Patnanugan (4,100 ha) and Jomalig. In the 1960s, large scale logging operations stripped the islands of forest. As a result, old growth lowland rainforest is reduced to less than 200 ha on Polillo Island, where primary or disturbed lowland forest is protected in two watershed reserves recognized by DENR (in Polillo and Panukulan), and in a watershed forest in Burdeos. There are areas of degraded forests at Anibawan and Burdeos adjacent to the Panukulan watershed reserve, which is one of the few remaining intact secondary forests in northern Polillo. The watershed reserves are interconnected by patches of second growth along the ridges that form the central mountains of Polillo, which results is a network of forest patches and corridors of secondary forest and second growth vegetation, mixed with plantations. Mt Malulod, the highest point at 350 m, is largely deforested, but a few forest patches survive and many areas are now covered by mixed coconut plantation and secondary forest. On Patnanungan Island, most of the original forest has been converted to coconut plantations, although some isolated patches of lowland rainforest survive, and many of the plantations are now abandoned and being overrun by second growth. Minasawa Island Game Refuge and Bird Sanctuary contains relatively good beach forest. The best quality closed canopy forests in the islands are well protected in the Polillo watershed in the center of the main island, as they provide valuable potable water for the municipality of Polillo.
Several of the threatened and restricted-range birds of the Luzon Endemic Bird Area have been recorded in the Polillo island group. The large numbers of Philippine Duck that were recently seen on Jomalig represent an important population of this declining species, and the wetlands and marshes there and on Polillo Island are feeding areas for migrant shorebirds of more than 25 species. The islands also support one of the few remaining populations of Philippine Cockatoo in Luzon and its satellite islands, but their numbers have clearly declined substantially there. Seven subspecies of bird are endemic to Polillo, all of which were recorded there during a survey in 1996: Crested Goshawk Accipiter trivirgatus castroi, Blue-naped Parrot Tanygnathus lucionensis hybridus, Blue-backed Parrot Tanygnathus sumatranus freeri, Philippine Trogon Harpactes ardens minor, Luzon Hornbill Penelopides manillae subnigra (see above), Greater Flameback Chrysocolaptes lucidus grandis and White-browed Shama Copsychus luzoniensis parvimaculatus. Many of the small islands in the Polillo group are breeding areas for terns, pigeons and herons. Burdeos Bay may be an important feeding area for seabirds, as two species of shearwaters and hundreds of Great Crested-tern Sterna bergii were sighted there in January-June 1996. Great Crested-terns probably nest on Manlanat Island and they were previously known to nest in Kanaway Island ("Tern Island").
Non-bird biodiversity: Mammals recorded in the area include endemic species such as Philippine Brown Deer Cervus mariannus, Philippine Warty Pig Sus philippensis and Large Rufous Horseshoe Bat Rhinolophus rufus. Some of the smaller islands of this IBA are reported to have roosting colonies of flying foxes which may include the threatened endemic Golden-crowned Flying Fox Acerodon jubatus. The coastal areas around this IBA are said to support several species of marine mammals, including the endangered Dugong Dugong dugon. The globally threatened endemic Gray’s Monitor Lizard Varanus olivaceus and Sailfin Lizard Hydrosaurus pustulatus are known to occur in the area. The Green Smooth-scaled Gecko Pseudogekko smaragdinus, Polillo Calotes Calotes marmoratus sanchezi and Polillo Forest Frog Platymantis polilloensis are known only from this IBA.
BirdLife International (2020) Important Bird Areas factsheet: Polillo Islands. Downloaded from http://www.birdlife.org on 26/10/2020.