Rennell and Ontong Java are relatively isolated from other islands in the Solomons (see [Fig. 17]). Only one kind of bat (Pteropus howensis) is known from Ontong Java and apparently is endemic to that atoll. Pteropus tonganus geddiei, one of the megachiropterans that occurs on Rennell ([Table 5]), also is found in the New Hebrides and on New Caledonia ([Table 4]). This makes P. t. geddiei the only megachiropteran bat in the Solomons that is more closely related to bats on islands to the southeast of the Solomons than to bats on other islands of the Solomons, the Bismarcks, or New Guinea, to the north and west. The other species of megachiropterans (Dobsonia inermis and Pteropus rayneri) on Rennell are found also on other islands in the Solomons. It is to be noted that Mayr (1931) regarded the avifauna of Rennell as most nearly like that of the New Hebrides and New Caledonia. He suggested that the prevailing winds from the southeast have been important for birds that have reached Rennell. The New Hebrides and New Caledonia are four and a half times farther from Rennell than are San Cristobal and Guadalcanal. On first consideration a person might doubt that the winds would be favorable enough to compensate for the great distance between Rennell and the New Hebrides and New Caledonia. Darlington (1938) has used the formula X n/m to obtain a comparison of barriers of different widths. [X = the probability of an individual crossing a barrier of width m; the probability of an individual crossing a similar barrier of width n is the ratio n/m.] If this formula is applied here, one finds that winds from the southeast (that is, from the New Hebrides and New Caledonia) would have to be more than 100 times more favorable than winds from the northeast (from Guadalcanal and San Cristobal) in order to compensate for the distance of Rennell from the New Hebrides and New Caledonia. Even so, tropical storms with unusually strong winds, frequent during some parts of the year, possibly account for the present distributional pattern of bats and birds that live on Rennell.
Whatever the means by which bats of the species P. tonganus reached Rennell, the fact remains that specimens from Rennell cannot be distinguished from specimens of P. tonganus geddiei from the New Hebrides and New Caledonia, more than 500 miles to the southeast.
Note: An important and interesting paper on zoogeography of bats, which was published too late to be included here, is: Krzanowski, A., 1967, The magnitude of islands and the size of bats (Chiroptera), Acta Zool. Cracoviensia, 12:281-348.
LITERATURE CITED
Anonymous.
1944. Gazetteer of Solomon Islands, Bismarck Archipelago, and Islands of the south-eastern end of New Guinea. Hydrographic office of the United States Navy Department, No. 881.
Andersen, K.
1908. Twenty new forms of Pteropus. Ann. Mag. Nat. Hist., ser. 8, 2:361-370, October.
1909a. On the characters and affinities of "Desmalopex" and Pteralopex. Ann. Mag. Nat. Hist., ser. 8, 3:213-222, February.