Mariana Fruit Bat

Pteropus mariannus / Fanihi
Mariana fruit bat

Mariana fruit bats, also known as flying foxes or fanihi, are medium-sized bats with dark fur. The males are slightly larger than the females, and 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.

The Mariana fruit bat (Pteropus mariannus) is often confused with the little Mariana fruit bat (Pteropus tokudae), a Guam endemic which is a much smaller species than the Mariana fruit bat - measuring 140 to 151 mm, with a wingspan of 650 to 709 mm. The little Mariana fruit bat, however, has not been observed since 1968 and is now thought to be extinct.

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.

Mariana fruit bats are frugivorous, feeding on fruits and occasionally flowers and leaves. Fanihi 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. Bats gradually depart colonies for several hours around sunset to forage. 

The species is polygynous - meaning that males often form harem groups wherein a male is usually accompanied and mates with multiple females. Reproduction occurs year-round and given the long gestation period of 4.5-6 months, females tend to birth one offspring per year. 

Once found throughout the Mariana Islands, 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 under the Endangered Species Act.

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. During a count CNMI-wide in 2000, findings yielded an estimated total of around 4,500 bats.

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, illegal 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 young bats, and may contribute to the lack of recruitment of young bats into the single remaining colony on Guam.

Facts About Mariana Fruit Bat

Listing Status

Threatened

Average Lifespan

Unknown; Captivity: 30 yrs

Reproductive Age

6-18 months of age

Diet

Fruits including breadfruit, papaya, fadang, figs, kafu, talisai, flowers, and leaves

Size

Length: 195-250 mm (7.7-9.4 in); Weight: 330-577 g (0.7-1.3 lbs); Wingspan: 860-1065 g (33.9-42 in)