Pteropus samoensisSamoan flying fox

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Geographic Range

Pteropus samoensis is endemic to the Samoan and Fijian archipelagos of the South Pacific. Two distinct subspecies have been recognized. The first, P. s. nawaiensis, is found in Fiji on Nauai, Ovalau, Taveuni, Vanua Levu, and Viti Luvu islands. The other subspecies, P. s. sameonsis is found living on the major Samoan islands; Savaii and Upolu in Western Samoa and Tutuila, Ofu, Olosega, and Ta'u in American Samoa. (Brooke, 2001)

Habitat

This species roosts and forages in primary forests. Roosts are often found along ridge tops. The bats tend to evenly space their roosts across these ridges and locate them in trees that are clear of understory. This allows for a clear drop-off exit. The ideal drop-off exit can also be found in trees that grow along roadsides, on the edges of plantations, and open pastureland. (Banack, 2001)

Physical Description

Pteropus samoensis is a medium sized flying fox. Adults typically weigh between 400-500 grams and have a forearm length of 130-150 mm (Brooke, 2001). The body and wings of this bat tend to be dark brown in color with variations in fur color ranging from blonde to grey on the head, neck, and shoulders (Brooke, 2001). Banack (2001) described the hairs of the fur as, "seal brown at base with lighter tips" with "pale-colored (yellowish to grayish white) hairs sprinkled throughout."

Skull characteristics: The mandible length of this species is 44.0-49.2 mm and the coronoid process height is 25.2-28.7 mm. The basal ledges of the cheek teeth are strongly developed compared to other species of the genus Pteropus. The dental formula is i2/2, c1/1, p3/3, m2/3, with a total of 34 teeth. (Banack, 2001).

Wing specifications: P. samoensis has a wingspan (±SD) of 0.86 ± 0.04 m and a wing area of 0.11 ± 0.01 m2. The aspect ratio for the wings is 6.59 ± 0.12 and the wing loading is 33.08 ± 3.67 N/ m2 (Banack, 2001). Banack (2001) reported that, "P. samoensis soars despite wing morphology that is not specifically adapted for this behavior." Brooke (2001) observed frequent soaring above the tree tops that was comparable to that of a large hawk. (Banack, 2001; Brooke, 2001)

  • Range mass
    400 to 500 g
    14.10 to 17.62 oz
  • Average wingspan
    860 mm
    33.86 in

Reproduction

Pteropus samoensis females give birth to one young per year. This species has a long seasonal reproductive period that lasts from March through October, with the peak birthing times falling in May and June. Copulation can occur from August to December, with some occurring while females are still caring for large young. When juveniles become half the size of the adults, they begin to fly. Often times, the mother will still feed the young when they are three-fourths her size. (Banack, 2001)

  • Key Reproductive Features
  • gonochoric/gonochoristic/dioecious (sexes separate)
  • sexual
  • viviparous
  • Breeding season
    March through October
  • Range number of offspring
    1 to 1

Behavior

The Samoan flying fox has been observed roosting alone and in male-female pairs with the offspring of the current year. Roosts are dispersed throughout the forest. This species is considered to have a monogamous social organization, because repeated use of roost sites by pairs have been observed (Brooke, 2001). Sometimes larger groups, up to nine individuals, have been seen roosting at one place, but there are never the large aggregations that can occur with some bat species. (Banack, 1998).

This species is considered diurnal as members carry out most of their activities in the early morning and late afternoon. This characteristic may be a recent occurrence in the evolution of this species, as few or no other bat species are known to be diurnal. It may provide a mechanism to avoid predation in the roost by human hunters. Pteropus samoensis is also territorial. Individual male bats defend and advertise their territories, typically 2-4 km2, through aerial pursuits, vocalizations, scent marking, and wing displays. Banack (2001) described aerial pursuits as involving "chases between two animals and attacks in which the pursuing animal hits the fleeing animal with a wing or grabs the dorsum of the leading animal with its feet causing one or both animals to topple through the air and occasionally strike the vegetation below." This pursuit continues until the bat being chased leaves the territory. Males also scent mark their territories. They do this by rubbing neck gland secretions on the branches and trunks of trees. (Banack, 1998). (Banack, 1998; Banack, 2001; Brooke, 2001)

Communication and Perception

Individual male bats defend and advertise their territories, typically 2-4 km2, through aerial pursuits, vocalizations, scent marking, and wing displays (Banack, 2001). Males also scent mark their territories. They do this by rubbing neck gland secretions on the branches and trunks of trees (Banack, 1998). (Banack, 1998; Banack, 2001)

Food Habits

This species is considered a generalist. It feeds on 32 different plant species of which 91% grow in primary forest. Fruit is the main component of this bat's diet, but leaves and flower parts are also eaten. (Banack, 2001)

Predation

The most dangerous predators of Pteropus samoensis are humans. Humans hunt these bats when they are roosting. Owls and peregrine falcons may also prey on them in certain portions of their range. (Banack, 2001).

Ecosystem Roles

All flying foxes of the genus Pteropus play an important role as pollinators and seed dispersers. Brooke (2001) describes this well: "Particularly on small isolated islands with low biodiversity, flying foxes play an important role in maintaining forests by enabling seed and pollen dispersal. Loss of valuable flying fox populations may have a cascading effect on native forest ecosystems." Without flying fox species such as P. samoensis the dominant trees of these native forests would have a hard time regenerating and the genetic flow between different populations of each individual tree species would be greatly reduced (Banack, 1998). (Banack, 1998; Brooke, 2001)

  • Ecosystem Impact
  • disperses seeds
  • pollinates

Economic Importance for Humans: Positive

The genus Pteropus, as a whole, is responsible for the pollination and seed dispersal of 300 plants species in Southeast Asia, tropical Africa, and the Pacific Islands. Fujita (1988) established that humans use more than 450 products that are derived from 134 of these plants. Most of these plants are not grown in plantations; therefore, they absolutely rely on these bats for regeneration. Most of these products are used locally, but some are exported. Bananas provide a good example of the importance of these bats. Although the cultivated varieties do not require pollination for fruit development, most of the 20 known wild species do. These wild bananas are primarily pollinated by bats and these plants in turn, according to Fujita (1988), "provide important genetic reservoirs for cultivar improvement and for combating disease, such as fungal root rot." Some of the other plants pollinated by flying foxes may also have medicinal properties that have not yet been studied. (Fujita, 1998)

  • Positive Impacts
  • pollinates crops

Conservation Status

Pteropus samoensis experienced a dramatic population decline, 50-80%, in the late 1980s and the early 1990s (Banack, 1998). Since this species relies upon primary forest, it is very vulnerable to habitat destruction due to deforestation and hurricanes. Yet, commercial hunting has been the major contributor to the decline of this animal. In many Pacific Islands bat meat is considered a delicacy. Pteropus samoensis is one of the species that is preferred because of its superior taste and low number of ectoparasites. Rainey (1990) described the situation: "For the Chamorro people of Guam and the adjacent Commonwealth of Northern Marianas (CNMI), flying foxes are a traditional delicacy, served at birthdays and other personal and community social gatherings." The flying fox trade had been growing strong since the 1960s and 1981-1984 saw large exports of P. samoensis to Guam (Banack, 1998). Since then, this species has been listed as a Category 2 Candidate Endangered Species under the U.S. Endangered Species Act (Banack, 1998) and classified as endangered by the International Union for Conservation of Nature and Natural Resources (Brooke, 2001). Also, American Samoa and Western Samoa have both passed legislation to protect these bats from hunting and exportation. (Banack, 1998; Brooke, 2001; Rainey, 1990)

Contributors

Stacie Holmes (author), University of Michigan-Ann Arbor, Bret Weinstein (editor), University of Michigan-Ann Arbor.

Glossary

acoustic

uses sound to communicate

arboreal

Referring to an animal that lives in trees; tree-climbing.

bilateral symmetry

having body symmetry such that the animal can be divided in one plane into two mirror-image halves. Animals with bilateral symmetry have dorsal and ventral sides, as well as anterior and posterior ends. Synapomorphy of the Bilateria.

chemical

uses smells or other chemicals to communicate

diurnal
  1. active during the day, 2. lasting for one day.
endothermic

animals that use metabolically generated heat to regulate body temperature independently of ambient temperature. Endothermy is a synapomorphy of the Mammalia, although it may have arisen in a (now extinct) synapsid ancestor; the fossil record does not distinguish these possibilities. Convergent in birds.

folivore

an animal that mainly eats leaves.

frugivore

an animal that mainly eats fruit

herbivore

An animal that eats mainly plants or parts of plants.

island endemic

animals that live only on an island or set of islands.

monogamous

Having one mate at a time.

motile

having the capacity to move from one place to another.

native range

the area in which the animal is naturally found, the region in which it is endemic.

nectarivore

an animal that mainly eats nectar from flowers

oceanic islands

islands that are not part of continental shelf areas, they are not, and have never been, connected to a continental land mass, most typically these are volcanic islands.

pheromones

chemicals released into air or water that are detected by and responded to by other animals of the same species

rainforest

rainforests, both temperate and tropical, are dominated by trees often forming a closed canopy with little light reaching the ground. Epiphytes and climbing plants are also abundant. Precipitation is typically not limiting, but may be somewhat seasonal.

scent marks

communicates by producing scents from special gland(s) and placing them on a surface whether others can smell or taste them

sexual

reproduction that includes combining the genetic contribution of two individuals, a male and a female

tactile

uses touch to communicate

territorial

defends an area within the home range, occupied by a single animals or group of animals of the same species and held through overt defense, display, or advertisement

tropical

the region of the earth that surrounds the equator, from 23.5 degrees north to 23.5 degrees south.

visual

uses sight to communicate

viviparous

reproduction in which fertilization and development take place within the female body and the developing embryo derives nourishment from the female.

References

Banack, S. 2001. *Pteropus samoensis*. Mammalian Species, 661: 1-4.

Banack, S. 1998. Diet selection and resource use by Flying Foxes (Genus *Pteropus*). Ecology, 79: 1949-1967.

Brooke, A. 2001. Population status and behaviors of the Samoan flying fox (*Pteropus samoensis*) on Tutuila Island, American Somoa. Zoology, 244: 309-319.

Fujita, M. 1998. "Flying Foxes and Economics. BATS. Vol 6, No 1:4-9." (On-line). Accessed 01/08/04 at http://www.batcon.org/batsmag/v6n1-2.html.

Rainey, W. 1990. "The Flying Fox: Becoming a Rare Commodity. BATS. Vol 8, NO 1:6-9" (On-line). Accessed 01/07/04 at http://www.batcon.org/batsmag/v8n1-2.html.