Species Account: Pteropus samoensis

Pteropus samoensis is of the order Chiroptera, suborder Meagchirpotera, family Pteropodidae, subfamily Pteropodinae, and genus Pteropus (Altringham, 1996; Banack, 2001). It has two subspecies P. samoensis and P. nawaiensis (Banack, 2001). P. samoensis is commonly called the Samoan Flying Fox and is one of the old world fruit bats (Walker, 1994). The P. s. samoensis is found in the Samoan archipelago, on the islands of Savaii, Upolu, Tuluila, Ofu, Olosega, and Taπu (Banack, 2001). Where as, the P. s. nawaiensis is found on the Fiji islands of Nauai, Ovalau, Taveuni, Vanua Levu, and Viti Levu (Banack, 2001).

The P. samoensis usually has dark brown body and wings, though it ranges from dark brown to reddish brown and grayish black (Banack, 2001; Brooke, 2001). The necks of the Samoan flying foxes are colored lighter than the body with a yellowish white in the P. s. nawaiensis, and a more reddish brown or gray in the P. s. samoensis (Banack, 2001). The Samoan flying foxes are topped with a head of light fur varying from cream to gray (Banack, 2001). They have and average weight of 220 grams to 440 grams (Banack, 2001). An adult P. samoensis has a wingspan (+/-SD) of 0.86 +/- 0.04m and an average forearm length of 130 to 155mm. It has the ability to carry up to about 33.08 +/- 3.67 N/m² (Banack, 2001).

The reproductive season of the Samoan flying fox spans from August to January, with copulation occurring anywhere from August to December, but mainly September to October (Brooke, 2001; Banack, 2001). A peak in births occurs from May to June. P. samoensis has one offspring per year (Banack, 2001). The young are nourished by the mother for a longer time then most in the Pteropus genus, about 4 to 6 months, some still nourished at three-fourths adult size (Brooke, 2001; Banack, 2001). It is unknown whether of not P. samoensisπs remain with the same mate for more than a year, although it is unlikely according to Anne Brooke.

For half a year or more, the juvenile P. samoensis will roost with the mother (Brooke, 2001). P. samoensis will generally roost in a male female pair, with an offspring, or alone (Brooke, 2001). It is possible for several Samoan flying foxes to share one tree, but they are never found roosting in large groups (Banack, 2001). The Samoan flying foxes roost in forests in trees along ridge tops, cliff faces, and even road sides (Banack, 2001; Brooke, Solek, and Tualauleleia, 2000). This allows for an exit free of obstruction. The forest also provides access to food for the P. samoensis. Their diet is made up of fruit, leaves, and flower parts such as pollen, nectar, and blossoms (Banack, 2001). This diet has made the P. samoensis very important to the local environment (Nelson, Miller, Heske, and Fahey, 2000). They provide both seed dispersion and crosspollination for the local plants on which they feed (Banack, 2001; Fujita, 1988).

What is interesting about this bat is that it is diurnal, meaning it is active during the day, although it is still active during the night (Banack, 2001; Brooke, 2001). The P. samoensis can be seen out foraging in the early morning and late afternoon (Banack, 2001). This presents some interesting obstacles the P. samoensis has had to overcome. The most prominent being the risks of over-heating (Thomson, Brooke, Speakman, 1998; 2002). It is much hotter during the day then at night and this added to the heat created from continually flapping wings (Thomson, Brooke, Speakman, 1998). What the P. samoensis seem to have done to reduce the risk of over-heating is remain inactive during the hottest parts of the day (Thomson, Brooke, Speakman, 2002). In addition, to conserve energy they have developed the ability to soar (Banack, 2001; Thomson, Brooke, Speakman, 2002). However, P. samoenesisπs wings are not altogether adapted for this flying technique. Their wings appear to have developed a compromise between soaring, maneuverability and load carrying (Banack, 2001).

The Samoan flying fox is also territorial (Banack, 2001). A single P. samoensisπs territory can be 2 to 4 km² and during foraging, they will frequently defend entire trees (Banack, 2001; Brooke, 2001). The territory of a P. samoensis is marked by both vocalizations and scent markings from the bat (Banack, 2001, Brooke, 2001). The P. samoensis will rub its neck and chin on the trees in its territory using secretions from its neck gland to mark it (Banack, 2001). This was done on both fruit bearing trees and non-fruit bearing trees (Banack, 2001). Other ways of proclaiming its territory include threat displays (Banack, 2001; Brooke, 2001). A threat display would be a P. samoensis grabbing leaves and shaking them in its mouth and vocalizing with its wings spread open (Banack, 2001). The P. samoensis also uses its wings in the same way to sun itself (Brooke, 2001). This was accomplished by hanging in sunlight with its wings spread open (Brooke, 2001). When another bat threatens ones territory, the P. samoensis will react by initiating a chase (Brooke, 2001; Banack, 2001). The chase involves the chasing the intruder out of its territory, pursing it and striking it with its wings, grabbing it with its feet, and attempting to bite the intruder (Brooke, 2001; Banack, 2001). The intruder will undergo a series of rapid evasion, quickly changing directions and dodging its pursuer (Brooke, 2001), resembling an aerial dogfight of two enemy combatants. Another interesting behavior, although uncommon, happened when one P. samoensis actually attacked another perched on a tree or roosting, knocking it off (Brooke, 2001). This was done when an intruding bat landing on a fruiting tree, as well as during mating with courtship behavior (Brooke, 2001).

P. samoensis is a 2 Candidate Endangered Species (Banack, 2001). It has suffered many population declines due to cyclones and hurricanes, which destroyed much of the P. samoensisπs habitat (Banack, 2001). Unfortunately, this flying foxπs most dangerous threat is man. It has suffered greatly due to over hunting (Brooke, 2001). Flying Foxes, like P. samoensis, have been hunted on Guam and its surrounding islands as a delicacy, especially sought for special occasions (Rainy, 1990). By the 1960s over-hunting on Guam forced many other surrounding islands to be subjected to the flying fox hunters (Rainy, 1990). Some of these islands were very small with flying foxes as the only native mammal, with such small populations these islands quickly suffered from the hunting (Rainy, 2001). The biggest threat of the over-hunting, besides the extinction of the P. samoensis, is the harm extinction will due to the local plant life (Fujita, 1988; Nelson, Miller, Heske, and Fahey, 2000). Because the P. samoensis feeds on so many different fruits and other plants, it is relied on by all of these for seed distribution and cross pollination (Nelson, Miller, Heske, and Fahey, 2000). An extinction of P. samoensis would devastate this environment.

Action has been taken to prevent this from happening. Restrictions have been placed on hunting and exporting the Samoan flying fox in many places, such as Guam, American Samoa and Western Samoa (Banack, 2001). Its dwindling habitats have also been protected (Brooke, 2001). Although many hunters have simply moved to other areas where restrictions are less, the precautions being taken now will hopefully stop the decline of the species.

Bibliography

1.) Nowak, Ronald M. Walkerπs Bats of The World. Baltimore: John Hopkins University Press, 1991.

2.) Altringham, John D. Bats, Biology and Behavior. Hew York: Oxford University Press Inc, 1996.

3.) Brooke, Anne P., Christopher Solek, and Ailao Tualauleleia. ≥Roosting Behavior of Colonial and Solitary Flying Foxes in American Samoa (Chiroptera: Pteropodidae).≤ Biotropica (2000): Vol. 32, No. 2, pp. 338≠350.

4.) Thomson S. C., A. P. Brooke, and J. R. Speakman. ≥Diurnal activity in the Samoan flying fox, Pteropus samoensis.≤ Royal-Society-Philosophical-Transactions-Biological-Sciences. (1998): 353(1375): 1595-1606

5.) Nelson, S.L., M.A. Miller, E.J. Heske, and G.C. Fahey Jr. ≥Nutritional consequences of a change in diet from native to agricultural fruits for the Samoan fruit bat.≤ Ecography (2000): Vol. 23 Issue 4, p393, 9p

6.) Brooke, Anne P. ≥Population status and behaviors of the Samoan flying fox (Pteropus samoensis) on Tutuila Island, American Samoa.≤ Journal of Zoology (2001): Vol. 254, no. 3, pp. 309-319.

7.) Thomson, Susan C., Anne P. Brooke, and John R. Speakman. ≥Soaring behavior in the Samoan flying fox (Pteropus samoensis).≤ Journal of Zoology (2002): Vol. 256, no. 1, pp. 55-62.

8.) Fujita, Marty. ≥Flying Foxes and Economics.≤ Bats Magazine (1988): Vol. 6, no. 1, pp. 4-9.

9.) Rainey, William E. ≥The Flying Fox: Becoming a rare commodity.≤ Bats Magazine (1990): Vol. 8, no. 1, pp. 6-9.

10.) Banack, S. ≥Pteropus samoensis≤. Mammalian Species, (June 5, 2001): no. 661 pp. 1-4.

Joey Tercero

Feb. 23, 2004

Honors 278C Bats