A Prehistoric, Noncultural Vertebrate Assemblage from Tutuila, American Samoa1

David W Steadman2,3 and Gregory K. Pregill4

Abstract: Ana Pe'ape'a is a small cave on the southern shore ofTutuila, Amer­ ican . Excavations at Ana Pe'ape'a yielded 13,600+ bones of small verte­ brates, dominated (>95%) by the nonnative Pacific Rat, Rattus exulans. Represented in the owl-derived bone deposit are two species that no longer oc­ cur on Tutuila, the Pacific Boa (Candoia bibroni) and the Sooty Crake (Porzana tabuensis). Based on bone counts, C. bibroni was the second most common species at the site. The third most common, the Sheath-tailed Bat (Emballonura semi­ caudata), is extremely rare on Tutuila today. Compared with bone records in nearby , we believe that the deposit at Ana Pe'ape'a, with a radiocarbon date of A.D. 445 to 640, is at least 1,000 yr too young to be dominated by extinct species.

THE WEST POLYNESIAN faunal region com­ and Turner 1985]). Independent (formerly prises Fiji, Tonga, Samoa, and the outlying Western) Samoa comprises the very large is­ islands of Rotuma, 'Uvea, Futuna, 'Alofi, and lands of and Savai'i and their small Niue (Steadman 1993a, Steadman et al. offshore islands. American Samoa comprises 2000). Raised limestone islands in Fiji, Ton­ Tutuila, its offshore island of Aunu'u, the ga, and Niue have yielded rich deposits of Manu'a group (Ta'u, Ofu, Olosega), and the prehistoric bones in caves and rockshelters outlying atolls of Swains and Rose. that represent many extinct species or pop­ The wet volcanic soils of Samoa are well ulations of lizards, birds, and bats (Pregill suited for sustaining forests (Whistler 1980, 1993, Koopman and Steadman 1995, Pregill 1992, Elmqvist et al. 1994) but are not favor­ and Worthy 2003, Steadman in press). By able for bone preservation. Lava tubes have contrast, information on prehistoric verte­ produced extensive prehistoric bone records brates is very sparse in nearby Samoa (Figure in the Hawaiian Islands (James et al. 1987, 1), which lacks limestone and instead consists James and Olson 1991, Olson and James mainly of young basalt-rich volcanic rocks 1991) and the Galapagos Islands (Steadman with radiometric (4OK_ 40Ar) ages no older 1986, Steadman and DeLeon 1999), but Sa­ than ca. 2.8 ± 0.20 million yr (from Upolu moan lava tubes are poorly suited for bone [Simkin et al. 1981, Keating 1985, Natland deposition and preservation because of flow­ ing water, wet soils, and stagnant air saturated with humidity (Thomson 1921, Kear and Wood 1959, Hoch and Asche 1988). Archae­

1 Financial support came from the National Science ological excavations even at the relatively dry Foundation (grant EAR-9714819 to D.W.S.). Manu­ entrances of the Falemauga Caves on Upolu script accepted 26 January 2004. are not known to have yielded bones (Free­ 2 Florida Museum of Natural History, University of man 1944). Florida, Gainesville, Florida 32611. 3 Corresponding author (phone: 352-392-1721 x261; Thus, on 21 April 1999, it was a nice sur­ fax: 352-846-0287; e-mail: [email protected]). prise to discover a small but dry accumulation 4 Department of Biology, University of San Diego, of bone-rich sediment in a cave on Tutuila. 2 San Diego, California 92110. At 141.97 km , Tutuila is the largest island in American Samoa but still about an order of Pacific Science (2004), vol. 58, no. 4:615-624 magnitude smaller than Upolu or Savai'i. © 2004 by University of Hawai'i Press Here we describe the results of this discovery, All rights reserved which represents Tutuila's only evidence of

615 616 PACIFIC SCIENCE· October 2004

25 0 25 50 km INDEPENDENT SAMOA , ',1,',',1 I I 10 0 ~ ~'~POIU AMERICAN SAMOA /" .;.---• Nu'utele Ofu Olosega 170":WW ~ ~~tuila VJ Ta'u J MANU'A ISLANDS TUTUILA

15'5 170"5O"W

FIGURE 1. The location ofAna Pe'ape'a, Tutuila, American Samoa, in a regional and local context. prehistoric vertebrates. Our findings also Unit 4 (100 by 100 by 8-10 em deep) was on generate a limited discussion of the historic a ledge on the cave's northeastern wall. Each biogeography of Samoan and birds. Excavation Unit reached the basaltic bedrock of the cave. All excavation was by trowel. Levels are arbitrary vertical designations, MATERIALS AND METHODS whereas Layers reflect natural stratigraphic Ana Pe'ape'a (140 18' 24/1 S, 1700 41' 00/1 W) changes. During the excavations, on 22-23 is a small (ca. 24 m 2 of horizontal passage), April 1999, all sediment was dry-sieved in the seaward-facing cave of erosional origin at Ana field with screens of 12.5-,6.4-, 3.2-, and 1.6­ Pe'ape'a Point (alternative name Mata'ae mm mesh, thereby assuring recovery of the Point) on the south-central coast of rugged smallest identifiable specimens. Tutuila (Figure 1). It lies 200 m SSW of The bones are mostly dark reddish brown Matu'u Village and is visible from the coastal but vary in color from yellow to orange to highway (Figure 2). Only ca. 25 m inland black. In the field they were stored dry, sealed from and ca. 10 m above the sea, Ana Pe'ape'a in plastic bags (Whirl-pac, Nasco), and then presumably formed through wave action at a shipped to the Florida Museum of Natural time when the basalt escarpment was lower History (UF) to be cleaned, identified, and relative to sea level. curated. Identification of the bones was based The bones in Ana Pe'ape'a are mostly on comparisons with modern skeletons in UF from Excavation Units 1 and 2 (166 em long and the National Museum of Natural His­ by 30-80 cm wide by 18-40 cm deep), in tory, Smithsonian Institution (USNM), sup­ a small deposit of dry sediment on a ledge plemented for reptiles by specimens from along the cave's northern wall. Excavation the San Diego Natural History Museum Unit 3 (100 by 100 by 33-56 cm deep) was on (SDNHM). Although D.W.S. sorted all of the the main, central floor ofthe cave. Excavation non-Rattus bones from Ana Pe'ape'a, he did Prehistoric Vertebrate Assemblage from Tutuila . Steadman and Pregill 617

FIGURE 2. The entrance (upper right) of Ana Pe'ape'a, Tutuila, 22 April 1999. Jeffrey Sailer is walking in the left foreground. not pick out every bone ofRattus exulans from some wood charcoal and a single fragmentary the concentrated sediment matrix. Thus the premolar of a pig (Sus scrofa) in the top of numbers of bones in Table 1 are accurate for Layer II in Unit 3, and a calcaneum of a dog every species except R. exulans, for which at (Canis familiaris) in Unit 4. least several thousand additional bones were Based on the radiocarbon C4C) chro­ recovered but not counted. nology of human arrival in the Fiji-Tonga­ Samoa region (Kirch and Hunt 1993, Ander­ son and Clark 1999, Burley et al. 1999, RESULTS Steadman et al. 2002), the presence of bones of the nonnative Rattus exulans throughout Stratigraphy and Chronology the deposit at Ana Pe'ape'a should indicate The sediment at Ana Pe'ape'a consists of an age of less than 2,900-2,800 cal B.P. An poorly stratified, pebbly, cobbly silt. In Exca­ accelerator-mass spectrometer (AMS) 14C vation Units 1 and 2, it is loose, light reddish date (Beta-134572 [Figure 3]) is 1,505 to brown to dark brown, whereas in Excavation 1,310 cal B.P. (cal A.D. 445 to 640), based Unit 3 it is compacted and grayish brown in on purified collagen (acid-alkali pretreatment, Layer I, becoming less indurated and variably followed by ultrafiltration) from the femur more reddish in Layer II. The sediment in of a juvenile chicken (Gallus gallus). This Excavation Unit 4 is light to dark yellowish age is reasonable in light of the 19 taxa of brown. We found no artifacts or other cul­ vertebrates identified at Ana Pe'ape'a, which tural evidence, with the possible exception of include at least four that are introduced 618 PACIFIC SCIENCE· October 2004

Atmospheric data from Stuiver et al. (1998);OxCal v3.5 Bronk Ramsey (2003); cub r:4 sd:12 prob usp [chron]

1800 BP 1500±40 BP c: 68.2% probability .Q .... 1700 BP 1415 BP (66.2%) 1330 BP III c: 1320 BP (2.0%) 1310 BP 'E... 1600 BP 95.4% probability ~ 1520 BP (95.4%) 1300 BP '"0 c: 1500 BP o ..0... B 1400 BP o ~ a::III 1300 BP

1200 BP

1800CalBP 1600 CalBP 1400CalBP 1200 CalBP

Calibrated date

FIGURE 3. Calibration curve for the radiocarbon date (Beta-134572) from purified collagen of a chicken (Gallus gallus) femur from Ana Pe'ape'a, Tutuila.

(chicken, rat, dog, and pig), none that is ex­ Of the three bones referred to spp., tinct, and only two with populations that are the largest (a maxilla) came from a medium­ extirpated on Tutuila (a snake and bird; see large with an estimated snout-vent next section). length (SVL) of 110 mm. Three species of Emoia in that size range now inhabit Ameri­ Vertebrate Fauna can Samoa: Emoia lawesii, E. nigra, and E. sa­ moensis (Brown 1991). The last two occur All lizard taxa identified from Ana Pe'ape'a today on Tutuila. Our skeletal material of probably occur today on Tutuila. The gekko these three is limited to E. nigra, which Gehyra oceanica is common in American Sa­ corresponds in general morphology with the moa and has been recorded from all islands. fossil maxilla. An incomplete fossil dentary The Nactus pelagicus species group is a widely differs from that of E. nigra in details of den­ distributed complex of bisexual and unisexual tition; it came from an individual ca. 95 mm species of gekkos (Zug and Moon 1995, Zug SVL and probably represents one of the 1998). In most of N pelagicus is re­ other two species. Emoia samoensis is common stricted to parthenogenetic populations like on Tutuila (Schwaner 1980), whereas E. law­ those in American Samoa, where it is re­ seii is a cryptic, terrestrial species confined corded from Tutuila and Ta'u (Schwaner to coastal strands of coral rubble. Because it 1980, Amerson et a1. 1982b). occurs on Olosega, Ta'u, and tiny Aunu'u Prehistoric Vertebrate Assemblage from Tutuila . Steadman and Pregill 619

(Schwaner and Brown 1984), the absence of and tarsometatarsus) are from juveniles, sug­ E. lawesii from Tutuila is peculiar if it is not a gesting that this species nested near the cave. result of local extinction. The single bones of dog and pig at Ana The Pacific Boa, Candoia bibroni, is known Pe'ape'a certainly are not from predation by in American Samoa from about eight speci­ Tyto alba but may represent whose mens, all from Ta'u (Amerson et al. 1980). carcasses, whole or in part, were taken to the This snake also is known from Savai'i and cave by people, dogs, or pigs. Upolu, a disjunction of about 210 km from Ta'u. The fossils from Tutuila represent an DISCUSSION extinct population that helps to explain this Vertebrate Prehistory in Samoa otherwise illogical geographic hiatus. The Pacific Boa probably occurred throughout Roger Green and Janet Davidson conducted Samoa before people arrived. field surveys and excavations on the two The nine species of birds represent one largest and highest , Upolu introduced species (Gallus gallus), one seabird and Savai'i, from 1957 to 1967 (Green and (Proeelsterna eerulea), and seven indigenous Davidson 1969, 1974). Their excavations land birds. These land birds vary in habitat yielded few bones overall (mostly fish, dog, preference from forest edge and successional pig, or human), and they reported no habitats to mature forest, without any clear or bird bones that could be identified to spe­ trend. The only species of bird no longer cies (Green and Davidson 1969:241). In the found on Tutuila is the small, volant rail Por­ Auckland Museum in 1988, D.W.S. identified zana tabuensis. On other Polynesian islands 12 bones from their site on Upolu where it no longer occurs, P. tabuensis often as follows: nine from the chicken, Gallus gal­ survived into late prehistoric or historic times lus, two of the rail Gallirallus philippensis, and rather than being lost in Lapita times (Stead­ one of the tern Anous stolidus. Each species man 1993a, in press). The only native still exists on Upolu. Subsequent excavations mammal we found is the sheath-tailed bat on Upolu in 1974 yielded no bird bones Emballonura semieaudata, which is very rare on (Jennings et al. 1976). Tutuila today (Grant et al. 1994) but proba­ During 15 days exploring of lava tubes on bly roosted prehistorically in Ana Pe'ape'a. Upolu in April 1999, the only bird bones that We believe that the barn-owl Tyto alba was D.W.S. found were a few surface remains of responsible for the primary bone deposit the swiftlet Colloealia spodiopygia, which still (Excavation Units 1 and 2) because: (1) it is nests in the same caves. Thus we know noth­ the most commonly represented bird, in­ ing at all about prehistoric birds (or reptiles) cluding six bones of nestlings (two thoracic on two of the largest, highest, most culturally vertebrae, tibiotarsus, tarsometatarsus, two important, and species-rich islands in Poly­ pedal phalanges); (2) all other bones recov­ nesia. This is one of the most glaring and ered are of reptiles, birds, and mammals small challenging voids in the historic biogeogra­ enough to be eaten by T. alba (each of the phy of Polynesian vertebrates. four bones of the largest bird, the chicken, The situation is slightly better in American Gallus gallus, are from juveniles); (3) 95+% of Samoa, where only one site other than Ana the bones are of Rflttus exulans (Table 1), the Pe'ape'a has produced bones of indigenous preferred prey of T. alba in Oceania when vertebrates. The To'aga archaeological site 2 available (D.W.S., pers. obs.); and (4) no cul­ on Ofu, a small island (6.56 km ) in the tural evidence (artifacts, charcoal, features, Manu'a Group, dates from ca. 2,800 to 1,900 etc.) was found in the bone deposit. The few yr B.P. (see various chapters in Kirch and fish bones found in Units 3 and 4 are very Hunt 1993). No species of lizards or bats small and could represent food of the pisciv­ were recorded among the bones from To'aga orous tern Proeelsterna eerulea, which in turn (Nagaoka 1993); fishes and birds were the was consumed by the barn-owls. Three of the only indigenous vertebrates. The 74 bird 19 bones of P. eerulea (a humerus, tibiotarsus, bones identified from the To'aga site (Stead- 620 PACIFIC SCIENCE· October 2004

TABLE 1 The Bone Assemblage from Ana Pe'ape'a, Tutuila, Expressed in Numbers ofIdentified Specimens (NISP)

Units 1,2 Unit 3 Unit 4

Taxon Levell Level 2 Total % NISP Layer I Layer II Layer I

Fish Osteichthyes sp. 5 4 Reptiles Gehyra oceanica 25 9 34 <0.25 2 Nactus pelagiC11S 1 4 5 <0.04 Emoia spp. 3 3 <0.02 Lizard sp. 9 2 11 <0.08 2 Candoia bibroni 317 157 474 <3.47 Birds Gallus gallus n 2 2 4 <0.03 Procelsterna cernlea 11 8 19 <0.14 Porzana tabuensis 10 5 15 <0.11 GallirallzlS philippensis 1 1 <0.01 Tyto alba 14 10 24 <0.18 Halcyon chloris 2 1 3 <0.02 Foulehaio carunculata 1 1 <0.01 Aplonis tabuensis 1 1 <0.01 Aplonis atrifusca 1 4 5 <0.04 Bird sp. 26 15 41 <0.30 Mammals Emballonura semicaudata 105 35 140 <1.02 1 RflttzlS exulans n 9,481+ 3,413+ 12,894+ >94.29 5 6 7 Canis familiaris n 1 Sus serofa n 1 Total NISP 10,009+ 3,666+ 13,675+ 100 14 12 8 Sediment volume (liters) 81 33 114 74 218 30 Bone influx (per liter) 124+ 111+ 120+ 0.19 0.06 0.27

n Introduced species. man 1990, 1993b) represent 10 species of of Schwaner) mutilata, G. oceanica, Hemi­ seabirds, including five extirpated species of dactylus frenatus, Lepidodactylus lugubris, and shearwaters and petrels (Procellariidae). The Nactus (Cyrtodactylus of Schwaner 1980) pela­ five species of land birds from To'aga include gicus; the skinks Cryptobelpharus poecilopleurus the easternmost record of a megapode (Meg­ (Ablepharus boutonii of Schwaner 1980), Emoia apodius sp.: larger than M. pritchardii, smaller adspersa (Swains Atoll only), E. cyanura (pos­ than M. alimentum [Steadman 1993b, 1999]). sibly including its cryptic sibling E. impar [see Known from a fragmentary ulna and femur, Ineich and Zug 1991]), E. lawesii, E. nigra, E. this megapode is the only extinct species of samoensis (samoense of Schwaner), and Lipinia land bird recovered from the To'aga site. noetua; and one snake, the Pacific Boa, Can­ doia bibroni. Faunistics Each of the five species of gekkos is widely distributed in Oceania. The widespread The herpetofauna of American Samoa was skinks are Cryptobelpharis poecilopleurus, Emoia last reviewed by T. D. Schwaner as a part of cyanura, and Lipinia noctua. The other four vertebrate field surveys in 1975-1976 (Amer­ species of Emoia have circumscribed dis­ son et al. 1980, Schwaner 1980). The terres­ tributions in , with E. samoensis be­ trial herpetofauna includes the introduced ing endemic to American and Independent toad Bufo mm'inus; the gekkos Gehyra (Peropus Samoa. Considering as well the fossil data Prehistoric Vertebrate Assemblage from Tutuila . Steadman and Pregill 621

from nearby Tonga (Pregill 1993), it is likely Allor nearly all of the species that now that these six species of terrestrial reptiles are inhabit Independent Samoa but not American indigenous to American Samoa: Emoia ad­ Samoa probably used to live in both places. spersa, E. cyanura, E. lawesii, E. nigra, E. sa­ From Vpolu, Tutuila is easily visible to the moensis, and Candoia bibroni. Lipinia noctua east, with only 70 km of ocean separating probably is a prehistoric introduction (Austin these large, high islands. That all islands in 1999), whereas Gehyra mutilata probably ar­ American Samoa are smaller than Savai'i and rived through human agency in historic times Vpolu is unlikely to account for the dif­ (Fisher 1999). Hemidactylus frenatus has been ferences in species richness. Instead we be­ on central Pacific islands no more than 50 yr lieve that habitat modification and predation, (Moritz et al. 1993). Some of the remaining perhaps especially the former, may explain species of lizards may have dispersed natu­ American Samoa's much poorer avifauna. rally, such as G. oceanica (Zug 1991, Fisher Evidence for this comes from bird surveys on 1999), but the evidence is inconclusive. For small islands offV polu in April 1999 (Freifeld any Pacific island group with indigenous liz­ et al. 2001). The only one of these islands ards, the history of colonization for each spe­ with extensive mature forest is Nu'utele cies of lizard should be considered island by (Whistler 1983), which also has the richest island. avifauna. Apolima, with the same land area as More species of land birds have been re­ Nu'utele, supports a much less rich land bird corded in historic times (the past two cen­ community because it is inhabited (one vil­ turies) on Savai'i (31-32) and Vpolu (28) than lage of ca. 100 persons) and mostly defor­ on Tutuila, which has 17 species, more than ested. Five of the six species of land birds that any other island in American Samoa (Pratt et we found on Nu'utele but on no other off­ al. 1987, Steadman in press). The distribution shore islands are forest dwellers. These spe­ and relative abundance of modern land birds cies are more common in relatively mature in American Samoa are well documented forest than in more degraded habitats on (Amerson et al. 1982a,b, Banks 1984, Eng­ Vpolu and Savai'i (Bellingham and Davis bring and Ramsey 1989, Freifeld 1999), but 1988, Evans et al. 1992). Just as in the Vava'u the species composition is obviously artificial, Group of Tonga (Steadman and Freifeld whether compared with that of Independent 1998, Franklin et al. 1999), the columbids and Samoa or evaluated only among islands in passerines that are forest obligates can occur 2 American Samoa. Nearly all of the land birds on very small Samoan islands (::;;1 km ) as shared between the two Samoa's fall into long as much of the forest is intact. four broad categories: aquatic/semiaquatic/ Based in part on the age of the bone de­ grassland species (ducks, rails), predators posit at Ana Pe'ape'a (described here) and the (barn-owl, swiftlet), canopy frugivores (pi­ situation in Tonga (Steadman et al. 2002), it geons, doves, starlings), and canopy nectar­ is possible that much of the hypothesized ex­ ivores (lorikeets, honeyeaters). The only tinction of bird populations on Tutuila (and exception is the ground-dove Gallicolumba elsewhere in Samoa) took place within several stairi, although this species is extirpated or centuries of human arrival. Thus, although extremely rare anywhere in Samoa. Missing informative, the bones recovered from Ana from all ofAmerican Samoa are 13 species (in Pe'ape'a would have been even more so had 12 genera) known from Independent Samoa they been deposited at least a thousand years (Steadman in press), consisting of two rails earlier. (Poliolimnas cinereus, Pareudiastes pacificus), two columbids (Columba vitiensis, Didunculus stri­ ACKNOWLEDGMENTS girostris), and nine passerines (mostly under­ story insectivores). Six of these 12 genera For able field assistance during the exca­ (Didunculus and five passerines) occur today vations, we thank Holly Freifeld, Jeff Sailer, or formerly in Tonga (Steadman 1993a, in Epifania Suafo'a, and Sonny Taomia. Per­ press). mission to conduct the fieldwork was kindly 622 PACIFIC SCIENCE· October 2004 arranged by Epifania Suafo'a. For additional Engbring, J., and F. L. Ramsey. 1989. 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