Measurements.—External measurements of four males and one female are, respectively, as follows: Length of head and body, 134, 128, 134, 134, 136; tail vertebrae, 28, 23, 27, 26, 21; hind foot, 20, 16, 19, 16, 21; ear, 17, 17, 17, 17, 18; length of forearm, 73.8, 68.0, 74.0, 73.6, 78.0.
Remarks.—Nyctimene major scitulus has been recorded only from the western chain of islands in the Solomons (see [Fig. 15]). Specimens examined by me agree well in external dimensions and color with specimens described by Andersen (1912:712) and Troughton (1931:206-207).
De Beaufort (1951:113) considered bats of "less zoogeographical importance" than other mammals because the ocean is not an "absolute barrier to their dispersal." Volant animals are ecologically terrestrial and therefore are more nearly earthbound than De Beaufort's remarks would suggest (see Miller, 1966:10). Indeed, many kinds of volant animals are endemic to the Solomons. Birds, for example, are well adapted for flight but pose some of the most complex zoogeographic problems in the area of New Guinea and the Solomon Islands (Mayr, 1940:198; 1942:81-83; Koopman, 1957). Rapid speciation can take place in any situation where there is a high degree of isolation (Wright, 1931; Lack, 1947). In fact, isolation is a most important factor in speciation of insular populations (Baker, 1951:55). The one genus, nine species, and 19 subspecies of megachiropterans that are endemic to the Solomons ([Table 4]) obviously indicate that bats, although volant, can be restricted to one or more islands long enough for new taxa to evolve.
Table 4. A Summary of the Kinds of Megachiropteran Bats in the Solomon Islands and Their Affinities with Faunas of Adjacent Islands.
| Totals | Endemic to Solomons | Common only to Solomons and Bismarcks | Common to Solomons, Bismarcks, and New Guinea | Common to Solomons, New Hebrides, and New Caledonia | |
| Genera | 7 | 1 | 0 | 6 | 0 |
| Species | 16 | 9 | 1 | 6 | 1 |
| Subspecies | 20 | 19 | 0 | 0 | 1 |
The megachiropteran bats of the Solomons have their affinities with the fauna of New Guinea ([Table 4]); the Solomons and New Guinea have six genera and six species in common. Because the two areas never have been connected (via the Bismarck Archipelago) by dry land, bats probably have reached the Solomons by flying from island to island (see Durham, 1963:357, 359, 361, 363). Deignan (1963:266) has dismissed voluntary or involuntary flight as possible explanations for distributions of bats and birds on islands of the Pacific.
The taxonomic level of endemism can be used as an indicator of antiquity (Dobzhansky, 1941; Koopman, 1958:429-430). The one megachiropteran genus (Pteralopex) endemic to the Solomons apparently is an ancient relic. Bats of this monotypic genus occur on Bougainville, Choiseul, Santa Ysabel, and Guadalcanal (see [Fig. 4]). These four islands probably were contiguous during the maximum lowering of sea level in the Pleistocene (see Durham, 1963:362-363). Bats of the genus Pteralopex are the only kind in the Solomons having a distribution that can be correlated with former land connections between islands.
The distributions of 16 species of megachiropterans known from the Solomons are summarized in [Table 5] and in [Figure 16]. The larger islands (in terms of surface area and elevation) in general have the highest number of species (Guadalcanal 10, Choiseul 9, and Bougainville 8). But Fauro, one of the smallest islands for which data are available, has six species of megachiropterans whereas San Cristobal and Malaita, two of the larger islands, have only three and four species, respectively. Possibly this difference signals the need for additional collecting.
Bougainville and Choiseul, about 60 miles apart, have seven species of megachiropterans in common ([Table 5]). Fauro, 25 miles southeast of Bougainville and 35 miles west of Choiseul, shares five species with each of these islands ([Fig. 16]). Pteralopex atrata and Pteropus rayneri occur on Choiseul and on Bougainville, but not on Fauro. Individuals of these species are the largest fruit bats in the Solomons, and their absence on Fauro suggests, therefore, that this small island is ecologically unsuitable, at least in some months, for the support of populations of bats that require relatively large amounts of food. The small size of the island is consistent with this hypothesis, but several other islands as small as Fauro do support populations of the large kinds of Pteropus, at least in some months.