Fruit Bats

 

Fruit bats are one of the more unusual animals in American Samoa, especially for visitors from areas where bats are small and rarely seen. Three species inhabit our islands –two large fruit bats (Pteropus samoensis, P. tonganus) and a small insect-eating bat (Emballonura semicaudata).

 

Fruit bat with its young.

NPS

The two fruit bats are especially distinctive: they are renowned for being large (with a wing span up to 3 feet wide) and active both day and night. Pteropus samoensis (pe'a vao) is commonly called the Samoan fruit bat. It is presently found only in the Samoan Archipelago and Fiji. It once occurred inTonga but is now extinct there. The other fruit bat, Pteropus tonganus (pe'a fanua), has several common names such as the Insular, White-naped, White-necked or Tongan fruit bat. It has a wider distribution in the Pacific, ranging from islands near Papua New Guinea to the Cook Islands.

In American Samoa, fruit bats can be seen flying, soaring, feeding, or just hanging in trees. Although individuals of the two species overlap in size (adults weigh 300-600 grams), there are ways to differentiate them from a distance. When silhouetted against the sky, the pe'a vao has a more triangular shape, with wings that are slightly scalloped and relatively dark and opaque. Their flight appears more relaxed, usually with slower wing beats and deeper wing strokes. It is not unusual to observe them soaring in the air in the day, taking advantage of rising currents of warm air (thermals) to seemingly float up and about without flapping their wings.

 

Fruit bats taking care of their young.

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In contrast, pe'a fanua has a more cross-like appearance: the neck and head appear more pronounced, the wings are narrower and more scalloped, and the hind legs stretch out like a tail. In flight, pe'a fanua tend to have faster wing beats and shallower wing strokes. They are less likely to soar in thermals and generally take a directional route to and from roosting sites at dawn or dusk.

Despite these differences, it takes a keen eye to distinguish the two species from a distance. Close up, the pe'a vao may sport a white to yellowish triangular patch that starts from the forehead and extends to the back of its head, or it may simply exhibit a generally grayish head with or without flecks of white hair (much like a graying man). Its neck and shoulder areas are a beautiful russet brown, while the rest of the body has a dusty black appearance. The pe'a fanua, on the other hand, has a basically black head and body. These black areas serve to set off a distinctive band of creamy yellow on the back of the neck and which extends slightly below its shoulders as if in a cape. This explains why they are called white-naped fruit bats although the color is not really white.

 

Fruit bats roosting during daytime.

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The two species have quite different social behaviors.During the daytime, pe'a fanua form large roosting groups or colonies of hundreds to thousands of bats. These colonies are generally organized according to their reproductive status and may be composed of bachelor males, clusters of females defended by an adult male (suggesting a harem mating system), or groups of females and their young. In any case,individuals appear to be relatively "faithful" to their roosts, usually returning to their respective colonies following foraging flights.

But the pe'a vao does not do this. Instead, these bats usually roost singly on branches, or as pairs of males and females (suggesting a monogamous mating system), or as a female with its young. When roosting, pe'a vao males tend to hang from exposed or dead branches of trees on ridge tops while females roost in more covered positions on forest slopes.

The care and energy that both bat species put into their young is remarkable. Pregnancy lasts approximately 5months in both species, and once the young are born, it takes at least another 3 months before they are weaned.Even after they are capable of flight, the young continue to receive parental care, perhaps until they reach adult size or become reproductively active themselves. We know this from observations of pairs of individuals seen to alight independently on the same tree and subsequently come together with one individual (presumably the juvenile) being wrapped up in the other's wings as they settle down to roost. Sightings of pregnant females and individuals carrying young in flight indicate that pe'a vao give birth mostly between April and June. Pe'a fanua births appear to occur year-round but are more common in January and June to August.