Chapter 4

Specimens examined(nine males, one female; nine in alcohol, nine crania extracted and cleaned).—Bougainville in December, AM-M. 5786 (paratype); Guadalcanal in May, 23812, 23815, 23827; Kolombangara in January and February, 23369, 23381, 23388, 23406, 23444, 23456.Measurements.—SeeTable 3.

Measurements.—SeeTable 3.

Remarks.—Heretofore,Nyctimene albiventer bougainvillewas not known from Kolombangara and Guadalcanal. The subspecies apparently ranges throughout the western chain of the Solomons.

Troughton (1936:350) consideredNyctimene bougainvillespecifically distinct from its nearest ally,N. papuanus. Pohle (1953:130) did not examine specimens of either kind, but on the basis of Troughton's description decided thatN. bougainvillediffered only subspecifically fromN. papuanus. Laurie and Hill (1954:46) synonymizedbougainvilleandpapuanuswithN. albiventer. However, Troughton (1936:350) pointed out that in addition to sizebougainvillediffered frompapuanusby having narrower and longer pm3 and pm4. Judging from specimens examined by me, such is the case, and the difference is even more pronounced in m1.

Specimens ofN. a. bougainvillefrom Kolombangara and Guadalcanal agree with a paratype of this subspecies from Bougainville. Geographic variation, if present in the population in the western chain of islands (seeFig. 12), is slight and not notable in the series available. Some individual variation was found, especially in the shape of the interorbital region of the skull. An adultmale from Kolombangara is unusually dark, almost black; color of the other specimens (all in alcohol) is consistent according to sex.

Nyctimene albiventerfrom Choiseul and Santa Ysabel is smaller, in all respects, thanN. albiventerfrom Bougainville, Kolombangara, and Guadalcanal (seeTable 3), and therefore may be named and described as follows:

Nyctimene albiventer minor, new subspecies

Type.—Adult male, skin and skull, in good condition (originally stored in alcohol for about one year), no. BSIP 23636, Bernice P. Bishop Museum; from Choiseul Island, British Solomon Islands Protectorate; obtained on 11 March 1964, by Philip Temple, original number 1441.

Distribution.—Known only from Choiseul and Santa Ysabel islands (seeFig. 12).

Diagnosis.—Small forNyctimene; wing membranes brown with scattered yellow spots (dried specimens); uropatagium, feet, and ears brown; dorsum of tibia set with hair, ventral surface naked; dorsum of uropatagium sparsely set with pale brown hairs, ventral surface almost bare; fringe of hairs along two centimeters of dorsal and ventral surfaces of trailing edge of wing membrane; proximal third of dorsal surface of forearm sparsely set with hairs; pelage of back soft and thick, of medium length (about 7); hair on crown and nape short (about 4); well-defined black dorsal stripe, extending from uropatagium to shoulders; skull resembling that of other subspecies ofN. albiventerbut relatively smaller; zygomatic arch delicate, slender anteriorly; P2 small (seeFig. 14). Sexually dichromatic as follows: male—dorsum Hair-Brown, bases of hairs darker; hair on throat sparse, medium length (about 6), Hair-Brown; fur along sides of abdomen Drab; female—dorsum having Buffy-Brown cast, some individual hairs Hair-Brown; shoulders Sayal-Brown; hair on throat sparse, Hair-Brown on throat and midline of abdomen; sides of abdomen Sayal-Brown.

Comparisons.—FromNyctimene major scitulus, the largest member of this genus in the Solomons,N. a. minordiffers in being smaller in all measurements taken; forearm averaging 54.8 as opposed to 73.5; greatest length of skull 28.2 as opposed to 37.0, and females pale brown instead of pale gray.

From nine adults ofNyctimene albiventer bougainvillefrom Bougainville, Kolombangara, and Guadalcanal,minordiffers as follows: averaging slightly smaller in all dimensions; forearm averaging 54.8 as opposed to 57.9; second metacarpal averaging 27.4 as opposed to 28.3; 5th metacarpal averaging 38.5 as opposed to 40.0; condylobasal length 26.7 as opposed to 28.0; length of mandibular tooth-row 10.3 as opposed to 10.9; mandible smaller (seeFig. 14); dorsal stripe fainter.

FromNyctimene albiventer papuanus, known from eastern New Guinea, New Britain, and the Admiralty Islands,minordiffers as follows: slightly smaller in most dimensions; forearm averaging 54.8 as opposed to 57.0; length of maxillary tooth-row 8.9 as opposed to 9.8; length of mandibular tooth-row 10.3 as opposed to 11.0; breadth across upper third premolars notably less (7.5 as opposed to 8.4).

N. a. minordiffers fromN. albiventer albiventerGray, which occurs about 800 miles to the west ofminor, in ways made apparent by the description by Andersen (1912:700-701).N. a. minoroccurs about 1500 miles eastward of the place from whichN. a. draconillaThomas, a subspecies essentially unknown to me, was named (see Laurie and Hill, 1954:46).

FromNyctimene sanctacrucis, known from the Santa Cruz Islands,minordiffers as follows: much smaller in all dimensions; forearm averaging 54.8 as opposed to 75; greatest length of skull 28.2 as opposed to 34.5; length of maxillary tooth-row 8.9 as opposed to 12.9.

Fig. 12.Distribution ofNyctimene albiventer bougainville() andN. albiventer minor(). For names of islands seeFig. 2.

Fig. 13.Scatter diagram comparing two subspecies ofNyctimene albiventer. One individual of specimens thought to be intergrades is as large as specimens ofNyctimene a. bougainville, whereas the other three intergrades are about the same size as specimens ofN. a. minor. Symbols representN. a. bougainville(),N. a. minor(), and intergrades assigned tominor(). For names of islands seeFig. 2.

Table 3.Average and Extreme Measurements ofNyctimene albiventer bougainvilleandN. a. minor.

Measurements.—Measurements of the two subspecies from the Solomons are given inTable 3. Some measurements of the type are as follows: Length of head and body, 108; tail vertebrae, 20.5; hind foot, 14.7; ear, 11.3; length of forearm, 55.1; 2nd metacarpal, 27.4; 3rd metacarpal, 39.0; 4th metacarpal, 37.5; 5th metacarpal, 39.1; greatest length of skull, 28.6; condylobasal length, 27.5; zygomatic breadth, 18.4; length of maxillary tooth-row, 9.0; length of mandibular tooth-row, 10.4.

Remarks.—Nyctimene albiventer minorclosely resemblesN. albiventer bougainville, differing from the latter mostly in size. Although adults ofminoraverage only slightly smaller than adults ofbougainville(seeTable 3), there is only slight overlap (about 0.2 at most) in most minimum dimensions of external and cranial features ofbougainvilleand corresponding maximum dimensions of externals and crania ofminor. The difference in size is clearly shown in Figs.13and14.

Four specimens ofNyctimene albiventerfrom Fauro herein are considered to be intergrades betweenN. a. bougainvilleandN. a. minor. As shown inTable 3, the specimens from Fauro average slightly larger than those ofminorfrom Choiseul and Santa Ysabel and slightly smaller than specimens ofbougainvillefrom Kolombangara and Guadalcanal. I have assigned the specimens from Fauro toN. a. minorbecause they generally are closer tominorin size (seeFig. 13).

Specimens examined(five males and four females; seven in alcohol; seven crania extracted and cleaned).—Choiseul in February and March, 23636 (holotype), 23631, 23540, 23646; Santa Ysabel in February, 23539; Fauro in April, 23742, 23743, 23763, 23764.

One specimen ofNyctimenefrom Malaita Island is smaller thanNyctimene major, which is known from Shortland, Alu, Florida, New Georgia, Guadalcanal, Choiseul, and Malapa (seeFig. 15) and is larger than either of the two subspecies ofNyctimene albiventerknown from Bougainville, Fauro, Kolombangara, Guadalcanal, Choiseul, and Santa Ysabel. This specimen represents a previously unknown species and may be named and described as follows:

Nyctimene malaitensis, new species

Type.—Adult female, skin and skull, in good condition (originally stored in alcohol for about one year), no. BSIP 24103, Bernice P. Bishop Museum; from Malaita Island, British Solomon Islands Protectorate; obtained on 1 July 1964, by Peter Shanahan, original no. unknown.

Distribution.—Known only from Malaita (seeFig. 16).

Diagnosis.—Size average for genus but larger than closest relative,Nyctimene albiventer; wing membranes brown with scattered yellow spots (dried specimen); uropatagium, ears, and feet brown; dorsal surface of tibia set with hair, ventral surface bare; dorsal surface of uropatagium sparsely set with hair, ventral surface having few, scattered hairs; dorsal surface of trailing edge of wing membrane sparsely set with hairs, ventral surface bare; proximal third of upper- and under-surface of forearm set with hair; pelage of back luxuriant and soft (about 10 long); hair on crown and nape shorter than on back (4 to 8); well-defined black dorsal stripe from shoulders to rump (about 2 wide); basal half of most hairs on dorsum Deep Mouse Gray, distal half Light Buff, tips Ochraceous-Tawny; some hairs on back entirely Light Buff; hairs of crown Light Ochraceous Buff tipped with Ochraceous-Tawny; hair on throat and along sides of abdomen Light Ochraceous Buff; hairs of ventral midline Smoke Gray; braincase narrow; zygomatic breadth relatively narrow; well-developed lambdoidal crest in female; rostrum short, wide; upper canines slanted posteriorly; upper incisors large; foramen ovale large (seeFig. 14).

Fig. 14.Dorsal and ventral views of skulls of (A)Nyctimene albiventer minor[specimen 23631 ♂, (B)N. a. bougainville[specimen 23381 ♂], and (C)N. malaitensis[specimen 24103 ♀].

Comparisons.—FromNyctimene major scitulus, the largest kind ofNyctimenein the Solomons,malaitensisdiffers as follows: smaller in all dimensions (forearm 65 as opposed to 73.5); greatest length of skull 32.4 as opposed to 37.0; length of maxillary tooth-row 10.5 as opposed to 13.0; length of mandibular tooth-row 11.8 as opposed to 14.2.From nine adults ofNyctimene albiventer bougainvillefrom Bougainville, Kolombangara, and Guadalcanal,malaitensisdiffers as follows: larger in all dimensions: forearm 65 as opposed to 57.9; greatest length of skull 32.4 as opposed to 29.7; zygomatic breadth 20.4 as opposed to 19.2; and length of maxillary tooth-row 10.5 as opposed to 9.5; length of mandibular tooth-row 11.8 as opposed to 11.1.From five adults ofNyctimene albiventer minor, from Choiseul and Santa Ysabel,malaitensisdiffers in the same ways it differs fromN. a. bougainville, but the contrast is even greater whenmalaitensisandminorare compared.FromNyctimene sanctacrucis, known only from the Santa Cruz Islands,malaitensisdiffers in being smaller in all dimensions: forearm 65 as opposed to 75; greatest length of skull 32.4 as opposed to 34.5; and length of maxillary tooth-row 10.5 as opposed to 12.9.Measurements of the holotype.—Length of head and body, 118; tail vertebrae, 23.0; hind foot, 16.0; ear, 14.0; length of forearm, 65.0; 2nd metacarpal, 33.2; 3rd metacarpal, 46.4; 4th metacarpal, 44.3; 5th metacarpal, 46.0; greatest length of skull, 32.4; condylobasal length, 30.6; palatal length, 13.0; breadth of braincase, 12.5; zygomatic breadth, 20.4; interorbital breadth, 5.5; breadth across first upper molars, 9.5; length of maxillary tooth-row, 10.5; length of mandibular tooth-row, 11.8.

From nine adults ofNyctimene albiventer bougainvillefrom Bougainville, Kolombangara, and Guadalcanal,malaitensisdiffers as follows: larger in all dimensions: forearm 65 as opposed to 57.9; greatest length of skull 32.4 as opposed to 29.7; zygomatic breadth 20.4 as opposed to 19.2; and length of maxillary tooth-row 10.5 as opposed to 9.5; length of mandibular tooth-row 11.8 as opposed to 11.1.

From five adults ofNyctimene albiventer minor, from Choiseul and Santa Ysabel,malaitensisdiffers in the same ways it differs fromN. a. bougainville, but the contrast is even greater whenmalaitensisandminorare compared.

FromNyctimene sanctacrucis, known only from the Santa Cruz Islands,malaitensisdiffers in being smaller in all dimensions: forearm 65 as opposed to 75; greatest length of skull 32.4 as opposed to 34.5; and length of maxillary tooth-row 10.5 as opposed to 12.9.

Measurements of the holotype.—Length of head and body, 118; tail vertebrae, 23.0; hind foot, 16.0; ear, 14.0; length of forearm, 65.0; 2nd metacarpal, 33.2; 3rd metacarpal, 46.4; 4th metacarpal, 44.3; 5th metacarpal, 46.0; greatest length of skull, 32.4; condylobasal length, 30.6; palatal length, 13.0; breadth of braincase, 12.5; zygomatic breadth, 20.4; interorbital breadth, 5.5; breadth across first upper molars, 9.5; length of maxillary tooth-row, 10.5; length of mandibular tooth-row, 11.8.

Fig. 15.Distribution ofNyctimene malaitensis() andN. major scitulus(). For names of islands seeFig. 2.

Remarks.—In size,Nyctimene malaitensisis intermediate betweenN. albiventerandN. major. Because the type ofmalaitensisis brown and not pale gray, as are females ofmajor,N. malaitensismost likely is more closely related toN. albiventer, in which the females are brown. The teeth of the holotype and only known specimen ofmalaitensisare too worn to be useful in determining the relationships between these species.

When more specimens are available,N. malaitensismay prove to be a subspecies ofN. albiventer. At present,malaitensisis accorded specific rank in order not to obscure the apparent relationships ofN. albiventer bougainvilleandN. a. minor. Additionally,N. malaitensisis given specific rank because (1) it is larger (especially in external dimensions) than the largest subspecies ofN. albiventer(compare above measurements with those inTable 3), and (2)malaitensisdoes not form a cline with either of the two subspecies ofN. albiventer.

Specimen examined(one female).—Malaita in July, 24103 (holotype).

Nyctimene major

This large species of tube-nosed bat has at least four subspecies, one of which (N. major scitulus) is endemic to the Solomons. The species occurs throughout eastern New Guinea and on many of the islands adjacent to theeastern coast of New Guinea, including the Trobriand Islands, the Bismarck Archipelago, and the Solomons (see Laurie and Hill, 1954:47). The geographic distribution of the species generally is the same as that ofN. albiventer.

InNyctimene major, as inN. albiventer, most males are grayish-brown, whereas most females are pale gray.

Nyctimene major scitulusAndersen

1910.Nyctimene scitulusAndersen, Ann. Mag. Nat. Hist., ser. 8, 6:623, December 1, type from Shortland; 1912, Andersen, Catalogue of the Chiroptera ... British Museum, 1:711, from Shortland, New Georgia, Florida, Guadalcanal; 1931, Troughton, Proc. Linnean Soc. New South Wales, 56:206, July 15; 1931, Sanborn, Publ. Field Mus. Nat. Hist., 18:22, February 12, from Choiseul and Malapa; 1942, Tate, Bull. Amer. Mus. Nat. Hist., 80:342, December 31.

1954.Nyctimene major scitulus, Laurie and Hill, List of land mammals of New Guinea, Celebes and adjacent islands, p. 47, June 30.

1862.Harpyia pallasi, Gerrard, Catalogue of the bones ... British Museum, p. 58.

1870.Harpyia cephalotes, Gray, Catalogue of monkeys, lemurs and fruit-eating bats in the British Museum, p. 121.

1878.Harpyia major, Dobson, Catalogue of the Chiroptera ... British Museum, p. 90; 1879, Trouessart, Rev. Mag. Zool., 3:207; 1887, Thomas, Proc. Zool. Soc. London, p. 323; 1888, Thomas, Proc. Zool. Soc. London, p. 476; 1897, Trouessart, Catalogus Mammalium ..., 1:87.

1899.Cephalotes major, Trouessart, Catalogus Mammalium ..., 2:1277.

1899.Gelasinus major, Matschie, Die Megachiroptera ... naturkunde, p. 84; 1904, Trouessart, Catalogus Mammalium ..., Suppl., p. 64.

Specimens examined(four males and one female; dried skins with skulls inside).—Florida in October, 24397, 24413, 24418, 24419.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.

Specimens examined(four males and one female; dried skins with skulls inside).—Florida in October, 24397, 24413, 24418, 24419.

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 scitulushas been recorded only from the western chain of islands in the Solomons (seeFig. 15). Specimens examined by me agree well in external dimensions and color with specimens described by Andersen (1912:712) and Troughton (1931:206-207).

ZOOGEOGRAPHY AND SPECIATION

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.

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 (viathe 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 (seeFig. 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 genusPteralopexare 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 inTable 5and inFigure 16. The larger islands (in terms of surface area and elevation) in generalhave 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 atrataandPteropus raynerioccur 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 ofPteropus, at least in some months.

Table 5.A Summary of Distribution of All Species of Megachiropteran Bats Known from the Solomons. Only Islands Well Known Faunistically Are Listed.

Santa Ysabel has six species of megachiropterans and 10 occur on Guadalcanal (Table 5). These two islands, separated by about 100miles of water, share five species (Rousettus amplexicaudatus,Pteralopex atrata,Pteropus rayneri,Dobsonia inermis, andNyctimene albiventer). The Nggela Group, in which Florida is the largest island and the only one from which bats have been collected, is 50 miles southeast of Santa Ysabel and 30 miles north of Guadalcanal (Fig. 16). Four species of megachiropterans are known from Florida (Dobsonia inermis,Macroglossus lagochilus,Melonycteris aurantius, andNyctimene major). Three of these are known from Guadalcanal and one occurs on Santa Ysabel. This situation resembles the one involving Fauro, Bougainville, and Choiseul because none of the large bats (PteropusandPteralopex) is known from Florida, even though two species of large bats that occur on Santa Ysabel to the northwest occur also on Guadalcanal to the south. Possibly Florida and the smaller islands that comprise the Nggela Group are ecologically unsuitable for large bats, or perhaps these small islands can support only limited numbers of individuals during part of a year.

Fig. 16.The number of megachiropteran species known from individual islands (number within a circle) is compared with the number of species common to two different islands (number without a circle). For names of islands seeFig. 2.

Some of the small islands in the Solomons have populations of large fruit bats. For example,Pteropus admiralitatumandP. hypomelanushave been reported from the small islands in the Russell Group (Table 5). Possibly these species do not live concurrently in the Russells; specimens of the two were obtained in different years. Two small megachiropterans,P. woodfordiandMelonycteris woodfordi, also inhabit the Russells. Shortland, a small island about 15 miles south of Bougainville, supports one large bat,P. admiralitatum, as well as smaller megachiropterans.

Kolombangara and Vella Lavella are about the same size and are separated by about 15 miles of water.Rousettus amplexicaudatus,Pteropus rayneri,P. woodfordi,Macroglossus lagochilus, andNyctimene albiventerhave been collected on Kolombangara but onlyP. admiralitatum,P. rayneri, andDobsonia inermishave been found on Vella Lavella. The difference in the known megachiropteran faunas is more striking when one compares each island with adjacent islands. Two species on Vella Lavella occur also on Choiseul, which is about 35 miles northeastward, and two species occur also on Shortland, which is 120 miles northwestward (Fig. 16). Four of the five megachiropterans on Kolombangara also have been found on Choiseul, about 50 miles northward (Table 5).Pteropus rayneriis the only megachiropteran known from both Kolombangara and Vella Lavella, even though the islands are separated by only a few miles of water. Inadequate data possibly account for the differences in the megachiropteran fauna, but I suspect that some other factors are involved. Although Vella Lavella and Kolombangara do have one species (P. rayneri) in common, a different subspecies occurs on each island—rubianuson Kolombangara andlavellanuson Vella Lavella (Fig. 17andTable 6). This indicates that some factor or factors are operating to keep megachiropterans from moving frequently or easily from one island to the other.

Each of several subspecies of species in the genusPteropusare known from one or two small islands separated by only a few miles from other islands on which different subspecies occur (seeFig. 6). Judging from this kind of distribution, these bats do not move frequently from island to island. Possibly this is because they cannot easily cross water barriers, or are not inclined to do so because food is abundantly available throughout the year on their homeisland. Because "flying foxes" frequently are seen in flight over water several hundred yards from shore, the first factor probably is unimportant—at least where short distances are involved. It seems most likely that when abundant food is available these bats have no reason to move even moderate distances.

Fig. 17.The number of subspecies of megachiropterans known from individual islands (number within a circle) is compared with the number of subspecies common to different islands (number without a circle). For names of islands seeFig. 2.

Distributions of subspecies of polytypic species are summarized inTable 6andFigure 17. Generally, more subspecies are known from the larger islands than from the smaller islands (Guadalcanal with 5, Bougainville, Choiseul, and Santa Ysabel with 4, Fauro with 2.) The distributions of some subspecies can be used to judge the differential effectiveness of water gaps between islands. The distribution ofPteropus rayneri lavellanusandP. rayneri rubianusis an example.

Choiseul and Santa Ysabel are separated by about 50 miles of water (seeFig. 17) but have three subspecies in common (Pteropus rayneri grandis,Dobsonia inermis minimus, andNyctimene albiventerminor.) Choiseul is about 50 miles from Kolombangara and about 35 miles from Vella Lavella, but shares no subspecies with these smaller islands although some species are shared (Tables5and6). From these data one can conclude that exchange of genes between populations on Choiseul and populations on Santa Ysabel is frequent but for some reason exchange of genes between populations on Vella Lavella and Choiseul and Kolombangara and Choiseul is infrequent. A series of small islands (Rob Roy, Wagina, and the Arnavon Islands, not named on the maps) connect Choiseul and Santa Ysabel in stepping-stone fashion (seeFig. 17). Possibly these small islands enhance movement of megachiropterans between Choiseul and Santa Ysabel.

Table 6.A Summary of Distribution of Polytypic Species of Megachiropteran Bats in the Solomon Islands. Only Islands Well Known Faunistically Are Listed.

Florida, of the Nggela Group, is approximately halfway between Santa Ysabel and Guadalcanal.Pteralopex atrata ancepsoccurs on Santa Ysabel and on Guadalcanal but is unknown from Florida. Fauro lies between Bougainville and Choiseul.Pteralopex atrata atrataandPteropus rayneri grandisoccur on Choiseul and on Bougainville but are unknown from Fauro. As suggested earlier, small islands like Fauro and Florida possibly cannot support large fruit bats, although they probably would utilize these small islands when in transit between larger islands.

Fauro apparently is important to the distribution of the two subspecies ofDobsonia inermisandNyctimene albiventerin the Solomons (see Figs.9and13). In both species, one subspecies is found in the eastern chain of islands and one subspecies is found in the western chain. Specimens ofDobsonia inermisfrom Fauro and Bougainville can be identified as the subspeciesinermiswhereas those from Choiseul are assignable to the subspeciesminimus.Nyctimene albiventer bougainvilleoccurs on Bougainville but specimens ofN. albiventerfrom Fauro and Choiseul can be identified as the subspeciesminor. Although interchange of genes occurs between populations on Bougainville and Fauro in the case ofD. inermis, the population ofN. albiventeron Fauro is at least partially isolated from the population on Bougainville.

Rennell and Ontong Java are relatively isolated from other islands in the Solomons (seeFig. 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 makesP. t. geddieithe 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 inermisandPteropus 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 morefavorable 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 speciesP. tonganusreached Rennell, the fact remains that specimens from Rennell cannot be distinguished from specimens ofP. tonganus geddieifrom the New Hebrides and New Caledonia, more than 500 miles to the southeast.

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