Endangered Species in the Pacific Islands

Mariana Fruit Bats / Fanihi

The Mariana fruit bat (Pteropus mariannus mariannus)  is a medium-sized bat measuring 195 to 250 mm from head to rump, with a wingspan of 860 to 1065 mm. The males are slightly larger than the females. The abdomen and wings are dark brown to black with individual gray hairs intermixed throughout the fur. The mantle and sides of the neck are bright gold on most animals but in some individuals, this region may be pale gold or pale brown. The color of the head varies from brown to dark brown.

Mariana fruit bat - Photo credit Dave Worthingtonl/USFWS

The little Mariana fruit bat (Pteropus tokudae) is much smaller than the Mariana fruit bat, measuring 140 to 151 mm, with a wingspan of 650 to 709 mm. The abdomen and wings are brown to dark brown but with few whitish hairs. The mantle and sides of the neck vary from brown to pale gold. The top of the head is grayish to yellowish brown while the throat and chin are dark brown. The bat is called "fanihi" in Chamorro, a language spoken in Guam and the Commonwealth of Northern Mariana Islands (CNMI).

Habitat & Behavior:
Mariana fruit bats are found in Guam and the CNMI. In northern Guam, bats primarily forage and roost in native limestone forest. Coconut groves and strand vegetation are other plant communities used occasionally for feeding and roosting. In southern Guam, a few fruit bats may still inhabit ravine forests. Farms, savannas, and mangroves are habitats that receive little or no use at present but may have been used commonly in the past when bats were more abundant and widespread on the island.

Fruit bats sleep during much of the day, but also perform other activities such as grooming, breeding, scent rubbing, marking, flying, climbing to other roost spots, and defending roosting territories (harem males only). Bats gradually depart colonies for several hours around sunset to forage.

The fruit bat feeds on a wide variety of plant material but primarily on fruits. It appears that the favored foods include the fruits of breadfruit, papaya, fadang, figs, kafu, and talisai and the flowers of kapok, coconut, and gaogao.

Past & Present:
Once found throughout the Mariana Islands, Mariana fruit bat populations have declined over the years, especially in the southern islands. They were first listed as endangered on Guam only, in the belief that bats on Guam formed a separate population segment from those on CNMI. Recent studies have indicated that the bats move from one island to another, linking these colonies as a single population. In 2005, the Mariana fruit bat was listed as threatened throughout its range.

The Mariana fruit bat once occurred throughout Guam in forested areas that formerly occupied most of the island. In 1958, a maximum of 3,000 bats were believed to be on Guam. Monthly counts on military lands in the 1960s indicated that the island's bat population was dropping.

Fewer than 1,000 bats were believed to exist in 1972 and less that 100 bats from 1974 to 1977. During an intensive islandwide survey in 1978 it was concluded that fewer than 50 fruit bats survived. A count done in 1984 produced an estimate of 425 to 500 animals. The most recent counts indicate that fewer than 50 bats remain in Guam. In the CNMI, counts on all islands in 1983 yielded an estimated total of approximately 8,000 bats. The most recent counts CNMI-wide (in 2000) yielded an estimated total of around 4,500 bats.

The Little Mariana fruit bat has always been considered rare and the last confirmed sighting of this bat was made in 1968. Thus, it appears that the little Mariana fruit bat may now be extinct. The introduction of firearms, the degradation and loss of primary and other forest habitats resulting from ungulate damage, invasion by alien plant species, predation by the brown tree snake on Guam, and economic development may lead to a reduction in the availability of resources critical for the survival and reproduction of fanihi and thus to a potential reduction in the number of bats that the remaining habitat is able to support.

Fanihi have been used as food since humans first arrived on the islands, and consumption of bats represents a significant cultural tradition. Overhunting, however, is cited as a causal factor in the initial fanihi declines on Guam, Saipan, and Tinian. Although hunting of bats has been illegal under local law in both Guam and the CNM1 since the 1970s, hunting remains a chronic threat.

The brown treesnake (Boiga irregularis), which has caused the extinction or extirpation of most native landbird species on Guam, is considered capable of preying on non-volant young bats, and may contribute to the lack of recruitment of young bats into the single remaining colony on Guam.

The small number of fanihi remaining on some islands (e.g., Guam and Saipan) may face significant risk of extirpation from natural disturbances, environmental changes, and other chance events to which small populations typically are vulnerable. Although this subspecies has evolved in the presence of natural disturbance, today a declining population and anthropogenic threats such as hunting erode the resilience of the population and reduce the likelihood of complete recovery in the wake of typhoons and volcanic eruptions. Typhoons, in particular, could eliminate bats that persist in small numbers on one or more of these islands. Military training activities such as live fire and aircraft overflight exercises in areas used by fanihi could disrupt the behavior of these bats. An increase in air traffic at Andersen Air Force Base, which harbors the single remaining fruit bat colony on Guam, is likely in conjunction with a base expansion that has been proposed and is currently under National Environmental Policy Act (NEPA) review.

Conservation Efforts:
Fruit bats received limited protection in 1966 when the Government of Guam ended year-round hunting of bats and established a 10-week hunting season for them. The Government of Guam has four conservation reserves that occupy about 4,200 acres of land for the protection of wildlife and native habitats. Additional protection was given to fruit bats in 1981 and 1984 when both species were placed on the Guam and United States Endangered Species Lists. The species were reclassified by the U.S. Fish and Wildlife Service from endangered to threatened status on Guam and newly listed as threatened in the CNMI on January 6, 2005.

The Guam National Wildlife Refuge provides protected habitat for the last remaining populations of the endangered Mariana fruit bats on Guam. The endangered Mariana crow and the endangered plant Serianthes nelsonii can also be found at the refuge.

The first Mariana fruit bat recovery plan was published in 1990, and a draft revised recovery plan was published in 2010.