Endangered and threatened species: Mariana fruit bat,

[Federal Register: January 6, 2005 (Volume 70, Number 4)]

[Rules and Regulations]

[Page 1190-1210]

From the Federal Register Online via GPO Access [wais.access.gpo.gov]

[DOCID:fr06ja05-14]

DEPARTMENT OF THE INTERIOR

Fish and Wildlife Service

50 CFR Part 17

RIN 1018-AH55

Endangered and Threatened Wildlife and Plants; Mariana Fruit Bat (Pteropus mariannus mariannus): Reclassification From Endangered to Threatened in the Territory of Guam and Listing as Threatened in the Commonwealth of the Northern Mariana Islands

AGENCY: Fish and Wildlife Service, Interior.

ACTION: Final rule.

SUMMARY: We, the U.S. Fish and Wildlife Service (Service), reclassify from endangered to threatened status the Mariana fruit bat (Pteropus mariannus mariannus) from Guam,

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under the authority of the Endangered Species Act of 1973, as amended (Act), and determine the Mariana fruit bat from the Commonwealth of the Northern Mariana Islands (CNMI) to be a threatened species under the authority of the Act. This rule lists the Mariana fruit bat as threatened throughout its range.

The Mariana fruit bat was listed previously as endangered on Guam. The bat populations on the southern islands of the CNMI (Aguiguan, Tinian, and Saipan) were candidates for listing. The best available scientific information indicates that Mariana fruit bats on Guam and throughout the CNMI comprise one subspecies. The protections of the Act, therefore, apply to this subspecies throughout its known range in the Mariana archipelago.

DATES: This final rule is effective February 7, 2005.

ADDRESSES: Comments and materials received, as well as supporting documentation used in the preparation of this final rule, will be available for public inspection, by appointment, during normal business hours at the Pacific Islands Fish and Wildlife Office, U.S. Fish and Wildlife Service, 300 Ala Moana Boulevard, Room 3-122, Box 50088, Honolulu, HI 96850.

FOR FURTHER INFORMATION CONTACT: Gina Shultz, Assistant Field Supervisor, Pacific Islands Fish and Wildlife Office (see ADDRESSES section) (telephone 808/792-9400; facsimile 808/792-9581).

SUPPLEMENTARY INFORMATION:

Background

The Mariana archipelago consists of the 15-island Commonwealth of the Northern Mariana Islands (CNMI) and the Territory of Guam, both within the jurisdiction of the United States. This archipelago extends 470 miles (mi) (750 kilometers (km)) from 13[deg]14' N, 144[deg]45' W to 20[deg]3' N, 144[deg]54' W and is approximately 900 mi (1,500 km) east of the Philippine Islands (Figure 1). Nine of the 10 northern islands (Anatahan, Sarigan, Guguan, Alamagan, Pagan, Agrihan, Asuncion, Maug, and Uracas) are volcanic in origin, and Farallon de Medinilla and the five southern islands (Guam, Rota, Aguiguan, Tinian, and Saipan) are uplifted limestone plateaus with volcanic outcrops. Mariana fruit bats have historically inhabited all of these islands except Uracas, the northernmost island (Wiles and Glass 1990). Of the largest southern islands (Guam, Rota, Tinian, and Saipan), Guam supports the majority of the human population. The northern islands (north of Saipan) are either unoccupied or support only a few families. The climate is tropical, with daily mean temperatures of 75 to 90[deg] Fahrenheit (24 to 32[deg] Celsius), high humidity, and average annual rainfall of 80 to 100 inches (in) (200 to 260 centimeters (cm)). Typhoons may strike the Mariana Islands during any month of the year, but are most frequent between July and October. BILLING CODE 4310-55-P

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[GRAPHIC] [TIFF OMITTED] TR06JA05.002

BILLING CODE 4310-55-C

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Species Description and Biology

The Mariana fruit bat is a medium-sized fruit bat in the family Pteropididae that weighs 0.66 to 1.15 pounds (330 to 577 grams) and has a forearm length ranging from 5.3 to 6.1 in (13.4 to 15.6 cm); males are slightly larger than females. The underside (abdomen) is colored black to brown, with gray hair interspersed, creating a grizzled appearance. The shoulders (mantle) and sides of the neck are usually bright golden brown, but may be paler in some individuals. The head varies from brown to dark brown. The well-formed and rounded ears and large eyes give the face a canine appearance; members of the family Pteropodidae often are referred to as flying foxes.

The Mariana fruit bat is highly colonial, forming colonies of a few to over 800 animals (Wiles 1987a; Pierson and Rainey 1992; Worthington and Taisacan 1995). Bats group themselves into harems (1 male and 2 to 15 females) or bachelor groups (predominantly males), or reside as single males on the edge of the colony (Wiles 1987a). On Guam, the average estimated sex ratio in a single colony varied from 37.5 to 72.7 males per 100 females (Wiles 1982).

Reproduction is believed to occur throughout the year in Pteropus mariannus yapensis on Yap (Falanruw 1988). Mating and the presence of nursing Pteropus mariannus mariannus young have been observed year- round on Guam (Perez 1972; Wiles 1983) with no apparent peak in births (Wiles 1987a). Glass and Taisacan (1988) suggested a similar pattern on Rota, but also indicated that a peak birthing season may occur during May and June, as has been observed in other fruit bats (Pierson and Rainey 1992). Female bats of the family Pteropodidae have one offspring per year (Pierson and Rainey 1992), pups may be born in any month of the year. Observations on Guam between July 1982 and May 1985 found 262 female bats, each with a single young (Service 1990). This reproductive rate, very low for a mammal of this size, results in a low maximum population growth rate, and thus a slow rate of recovery when a population is diminished (Pierson and Rainey 1992). Length of gestation and age of sexual maturity are unknown for the Mariana fruit bat; other related bats have a gestation period of approximately 4.6 to 6.3 months (Pierson and Rainey 1992). Age of sexual maturity is not known for the Mariana fruit bat, but Pteropus species typically do not breed before 18 months of age (Pierson and Rainey 1992).

Taxonomy and Interisland Movements

The fruit bats of the Mariana Islands consistently have been treated as one or more endemic subspecies or species; that is, they occur nowhere outside the archipelago (Andersen 1912; Kuroda 1938; Corbet and Hill 1980, 1986, 1991; Koopman 1982, 1993; Flannery 1995). Following the taxonomic treatments of Kuroda (1938) and Koopman (1993), which are known to be based on examination of numerous specimens, and the most recent treatment by Flannery (1995), Pteropus mariannus is a widely dispersed species occurring north of the equator in portions of Micronesia north to the Japanese Ryukyu Islands. Various authors have attributed different numbers of subspecies to P. mariannus. Kuroda (1938) and Koopman (1982, 1993) recognize seven subspecies; Flannery recognizes three.

Pteropus fruit bats are well known to be strong fliers and traverse long distances (Eby 1991; Palmer and Woinarski 1999; Nelson 2003). Evidence that Mariana fruit bats fly between islands in the archipelago supports consideration of these bats as a single subspecies made up of numerous island populations in the Marianas (Lemke 1986; Service 1990; Wiles and Glass 1990; Worthington and Taisacan 1996). The geography of the archipelago, as well as the flight capability of fruit bats, facilitates interisland exchange. Distances between islands in the Mariana archipelago range from 3 to 62 mi (5 to 100 km). Each island in the chain is visible from neighboring islands (Wiles and Glass 1990).

The August 27, 1984, Federal listing (49 FR 33881) of fruit bats resident on Guam was based on an assumption that these bats were a distinct subspecies isolated from other bat populations in the CNMI. However, current evidence exists that large numbers of bats from Rota have visited Guam for periods of months. Temporary spikes in the Guam fruit bat population were observed in 1992-1993 (from about 350 to 550 bats) and in 1998 (from about 150 to 760 bats) (Anne Brooke, Service, in litt. 2003). These temporary increases lasted for several months. More modest but equally sudden increases in the Guam population were noted 2 and 4 days following Typhoons Chataan and Pongsona, respectively, in 2002 (Dustin Janecke, University of Guam, in litt. 2003). The most likely explanation is a temporary relocation of bats from Rota, which lies 48 mi (77 km) from Guam, is visible from Guam's north shore, and harbors one of the largest fruit bat populations in the archipelago. For example, the 2002 spike on Guam after Typhoon Pongsona was concurrent with an observed dip in fruit bat numbers on Rota (Jake Esselstyn, University of Kansas (formerly CNMI Department of Fish and Wildlife (DFW)), pers. comm. 2004b). Several other instances of apparent immigrations from Rota to Guam documented in the late 1970s and 1980s are described in detail by Wiles and Glass (1990). Although we cannot be certain that ``visiting'' bats interbreed with resident Guam bats during their months on the island, the fact that Mariana fruit bats breed throughout the year (Wiles 1983, 1987a) leaves this possibility open. The presence of fruit bats on the islands of Tinian and Aguiguan, which are close to one another and to Saipan, is ephemeral (Worthington and Taisacan 1996), indicating that interisland travel likely occurs among these three islands as well.

An example of likely interisland movement in the northern islands of the CNMI comes from Sarigan. Fruit bat surveys on Sarigan documented a roughly stable level of approximately 125-235 bats between 1983 and 2000 (Wiles et al. 1989; Fancy et al. 1999; Wiles and Johnson 2004). In 2001, surveys estimated 300-400 bats (Wiles and Johnson 2004). Recruitment of juvenile bats alone cannot account for this increase, and Wiles and Johnson (2004) posit Anatahan, 23 mi (37 km) to the south, as the likely source for immigrants. Wiles et al. (1989) twice observed individual fruit bats 0.8 mi (2 km) from Guguan, flying south in the direction of Sarigan, which lies 39 mi (63 km) away. Anecdotal observations of likely transits among other northern islands are described in Wiles and Glass (1990) and by other species experts (Worthington and Taisacan 1996; Wiles and Johnson 2004).

Like fruit bats, many other highly mobile vertebrates of Pacific Islands, especially birds, are treated as a single species or subspecies inhabiting multiple islands in an archipelago (Mayr 1945; Pratt et al. 1987; Watling 2001). Immigration rates of perhaps one individual per generation could be necessary for an island population to maintain genetic homogeneity with the populations on other islands (Mills and Allendorf 1996; Wang 2004; Gary McCracken, University of Tennessee, pers. comm. 2004). The chances of witnessing such a low rate of immigration are slight. The evidence described above for interisland movement suggests even greater rates of movement and probable gene flow among the fruit bat populations on various islands in the Mariana

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archipelago than the minimum needed to maintain genetic homogeneity.

Preliminary results of a recent study of genetic variation in a similarly gregarious (Pierson and Rainey 1992) and mobile species of fruit bat elsewhere in the Pacific provide further, if circumstantial, support for the existence of a single subspecies of fruit bats in the Marianas. Genetic material collected from the white-collared fruit bat (Pteropus tonganus) in Samoa and Fiji shows a lack of genetic isolation within island groups (Utzurrum et al. 2000; G. McCracken, pers. comm. 2004). Little anecdotal observation of interisland movements exists for P. tonganus, yet apparently it experiences immigration at sufficient intervals to prevent genetic isolation.

Currently, there are two recognized subspecies restricted to the Mariana Islands: the Mariana fruit bat (Pteropus mariannus mariannus) and the Pagan fruit bat (Pteropus mariannus paganensis). Other subspecies are endemic to other archipelagos and do not occur in the Marianas. The taxonomic status of the Pagan fruit bat is questionable. Yamashina (1932) collected three male fruit bats and one female from the islands of Pagan and Alamagan in 1931, and stated: ``[t]his species, as compared to the Pteropus mariannus mariannus that inhabit Guam, is distinctly darker in coloration, having brownish wings.'' He made no further comparisons, and thus the distinction of this taxon is based on a single, equivocal interpretation of the coloration of four specimens. Although future studies may confirm the existence of a distinct taxon of fruit bats in the northern islands, at this time, based on the best available science including peer reviewer comments, we do not consider Pteropus mariannus paganensis as distinct from Pteropus mariannus mariannus to represent a single taxon.

Habitat

Mariana fruit bats forage and roost primarily in native forest and forage occasionally in coconut (Cocos nucifera) groves and strand vegetation (Wiles 1987b; Worthington and Taisacan 1996). Wiles (1987b) described six bat roost sites on Guam, all within native limestone forest. Major roost trees included Ficus spp. and Neisosperma oppositifolia. On Rota, fruit bats used primary and secondary limestone forest for roosting and foraging (Glass and Taisacan 1988). At least nine tree species were used for roosting, including Elaeocarpus sphaericus, Macaranga thompsonii, Guamia mariannae, Hernandia spp., Artocarpus mariannensis, Ficus prolixia, Barringtonia asiatica, Randia cochinchinensis, and the introduced Theobroma cacao (Glass and Taisacan 1988). A small bat colony also was observed roosting in Casuarina equisetifolia on Aguiguan (Worthington and Taisacan 1996). At least 22 plant species are used as food sources by the Mariana fruit bat. Food items include the fruits of 17 species of plants, especially the native Artocarpus mariannensis, Cycas circinalis, Ficus spp., Pandanus tectorius, Terminalia catappa, and the introduced Artocarpus altilis and Carica papaya; the flowers of seven plants, including the native Ceiba pentandra and Erythrina variegata, and the introduced Cocos nucifera; and leaf stems and twig tips of Artocarpus spp. (Wiles 1987a; Service 1990). Although Mariana fruit bats have been observed to feed on and roost in cultivated, introduced food plants, nonnative species make up only a small fraction of the plants they use (Wiles 1987b; Worthington and Taisacan 1996). Fruit bats are important components of tropical forest ecosystems because they disperse plant seeds and thereby help maintain forest diversity and contribute to plant regeneration following typhoons and other catastrophic events (Cox et al. 1992).

CNMI Southern Islands

The relatively large size and moderate topography of the southern islands led to their being, along with Guam, the most heavily populated and intensively cultivated islands in the archipelago. All of the southern Marianas are hypothesized to have been densely forested when first settled by humans some 3,500 years ago (Mueller-Dombois and Fosberg 1998). The loss and alteration of native habitats on these islands began with prehistoric cultivation, accelerated with the 17th century introduction of livestock and mechanized agriculture by Europeans, and likely peaked during the mid-20th century with landscape-scale habitat conversion by commercial agriculture, military infrastructure, and bombardment (Bowers 1950; Fosberg 1960; Stone 1970). This long continuous and intense human disturbance is reflected by the near absence of Mariana fruit bats from Saipan, Tinian, and Guam.

On Saipan and Tinian, agriculture and free-roaming livestock had converted much of the islands' forest to fields and pastures as early as the 18th century (Barrat 1988 in Stinson et al. 1992). Human populations on these islands increased steadily, and virtually all arable land was used to grow cash crops or food (Bowers 1950). Sugar plantations dominated the landscapes of Saipan, Tinian, and Aguiguan prior to World War II (Fosberg 1960). Saipan and Tinian were invaded during World War II, and during and after the war, bombing and extensive military development resulted in the loss of additional fruit bat habitat (Bowers 1950; Fosberg 1960). After the war, Saipan and Tinian were estimated to retain 5 and 2 percent native forest cover, respectively (Bowers 1950), and these proportions apparently were not significantly different in 1982 (Engbring et al. 1986). The introduction of nonnative species such as tangantangan for erosion control has left these islands dominated by alien vegetation that inhibits the growth of native forest (Fosberg 1960; Craig 1993). Feral ungulates are present on both islands, resulting in further degradation and fragmentation. Finally, Saipan is the most heavily populated and industrialized island in the CNMI (CNMI Statistical Yearbook 2001). Aguiguan was not invaded during the war, and has retained a greater proportion of its native forest (20 percent; Bowers 1950).

Similar to Saipan and Tinian, large areas of Rota were converted to sugar plantations in the early part of the 20th century (Fosberg 1960). Rota has more rugged topography, however, and was not invaded during World War II. These two factors are thought to explain the greater amount of native forest cover (25 percent) remaining on Rota following the war (Baker 1946; Bowers 1950). Engbring et al. (1986) estimated that roughly 60 percent of Rota's land area supported native vegetation in 1982. It is not clear whether Engbring's estimate represents some level of native forest recovery since Bowers' (1950) post-war estimate, or is a different interpretation and measurement of forest cover.

Most of Guam's native vegetation has been replaced by land development and invasive species. Guam is the population and commercial center of the archipelago, and commercial and residential development are ongoing. Like the other southern islands, parts of Guam were seeded with tangantangan following World War II to control erosion (Fosberg 1960). Large areas of southern Guam are dominated by savannas; these landscapes are thought to have originated as a result of aboriginal burning (Fosberg 1960). In 1981, northern Guam, which supports the last extensive native forest remaining on the island, was thought to retain no more than 37 percent native forest cover (Engbring and Ramsey 1984). Feral ungulates are abundant and

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widespread throughout the island and cause significant damage to all remaining native forest (Fosberg 1960; Stone 1970; A. Brooke, pers. comm. 2004). Lands owned by the U.S. Air Force (Air Force) at Andersen Air Force Base in northern Guam include the largest contiguous forested areas left in northern Guam; the Air Force permits hunting of feral ungulates on parts of the base (U.S. Air Force 2001).

CNMI Northern Islands

Compared with the history of habitat loss in the southern islands, degradation or loss of native forest in the northern islands of the CNMI is a recent phenomenon; therefore, these islands have retained more habitat to support Mariana fruit bats. Some of the northern islands have supported small human settlements, and most of these have been occupied only sporadically. Feral ungulates have been present in the northern islands only since the mid-20th century. For example, Anatahan has had feral goats and pigs for roughly 40 years (Kessler 1997), and forest degradation and erosion were observed to escalate sharply during the 1990s (Marshall et al. 1995; Kessler 2000a; Worthington et al. 2001), possibly because feral ungulate damage was exacerbated by El Nino-related drought in the late 1990s (Kessler 2000a).

Although changes in forest cover were not quantified, evidence from point photo monitoring and other land-based photography conducted on Anatahan in 1983, 1996, and 2000 documented widespread loss of forest, reduced canopy cover in remaining forest, and increased erosion resulting from feral ungulate damage (Marshall et al. 1995; Kessler 1997, 2000a; Worthington et al. 2001). An ungulate eradication project was begun in 2002, but was not completed when Anatahan volcano erupted in 2003. This eruption further compromised the island's forest habitat, and continuing volcanic activity has hindered completion of the ungulate eradication project. A large population of feral pigs still occurs on the island and some goats remain; aerial hunting for goats is ongoing (Curt Kessler, Service, pers. comm. 2004b). Some vegetation recovery has been observed as a result of goat control, but an invasive alien vine, Mikania micrantha, has spread rapidly and may inhibit the growth of native vegetation (C. Kessler, pers. comm. 2004b). This plant is known to smother and displace native vegetation on other Pacific islands (U.S. Department of Agriculture (USDA) 2004).

On Pagan, livestock was maintained in captivity by island residents until the volcanic eruption in 1981, when the human population was evacuated. In the subsequent 23 years, large populations of feral goats, pigs, and cattle have become established on the island and have caused significant damage (Rice and Stinson 1992; Kessler 1997). The degradation and loss of native forest on Pagan is thought to be occurring more rapidly on there than on Anatahan because of the added impact of cattle, which are absent from Anatahan (Kessler 1997). The reductions in fruit bat numbers on Pagan are attributed to feral ungulates causing major damage to the native forest and preventing its regeneration following the 1981 eruption, large areas especially in the northern part of the island being converted to grassland or devegetated and eroded (Kessler 1997), and the spread of the invasive tree Casuarina equisetifolia in monotypic stands (Rice and Stinson 1992; Cruz et al. 2000e). In 1992, Casuarina coverage in the upland areas of the island was estimated at roughly 60 percent (Rice and Stinson 1992). Although this tree is used for roosting by Mariana fruit bats (C. Kessler, pers. comm. 2004b), it does not provide food resources, and it likely displaces native forest, as it has done elsewhere in the Pacific (Cruz et al. 2000e; USDA 2004).

Vegetation surveys in 2000 on Agrihan, the third-largest of the northern islands, documented damage from feral ungulates in the 30 to 40 percent of the island that supports forest habitat (Cruz et al. 2000f). The extremely steep and dissected topography of Agrihan is thought to restrict the distribution of feral ungulates as well as access by humans, and keep goats and pigs geographically separated (Rice et al. 1990; Rice and Stinson 1992), thereby protecting roost sites and sufficient forest habitat to support foraging fruit bats.

Feral goats, pigs, and cattle are present on Alamagan and the extent of native forest remaining on the island is limited to ravines on the south and west slopes and a small plateau in the center of the island (Wiles et al. 1989). Rice (1992) described Alamagan as having ``one of the worst feral ungulate problems in the CNMI,'' and during vegetation surveys in 2000, Cruz et al. (2000b) found the remaining forests to be in decline.

Maug, Asuncion, Guguan, and (since 1998) Sarigan are free of feral ungulates, but the small size of these islands and the limited extent of their forest habitat ultimately limits the number of fruit bats they can support. Maug is only 10 to 14 percent forested (Wiles et al. 1989), and thus supports little habitat for fruit bats. Forest on Asuncion and Guguan is limited to the lower western and southern areas; the northern and steep upper parts of these islands are bare volcanic ash or grassland (Wiles et al. 1989). Roughly 32 percent or 400 acres (ac) (162 hectares (ha)) of Sarigan is forested, but most of this is monotypic coconut forest that provides only minimal forage for fruit bats; only about 72 ac (29 ha) supports relatively diverse native forest that provides both roosting and foraging resources for fruit bats (Wiles and Johnson 2004). Although the eradication of ungulates from Sarigan and initial vegetation recovery may play a role in increased numbers of fruit bats on the island, invasive, alien plants such as tangantangan (Leucaena leucocephala) and Operculina ventricosa also are present on the island and may impede the recovery of native forest over the long term (Kessler 2000b). These plants are known to degrade native vegetation in the Mariana Islands and elsewhere in the Pacific (USDA 2004).

Landownership of Fruit Bat Habitat in the Mariana Islands

Most of the known fruit bat roost sites in the Mariana Islands are located on public lands. On Guam, the single remaining roost and most fruit bat foraging habitat is found on U.S. military lands; some foraging habitat occurs on private lands and lands belonging to the Government of Guam (Wiles 1998). The Air Force controls access to Andersen Air Force Base in northern Guam, and the high security and frequent patrols practiced on base effectively create a refugium for fruit bats (Morton 1996). The remote and relatively pristine area where the roost is located was set aside by the military in 1973 as a research natural area; access to and activities in this area are tightly restricted, but no brown treesnake control currently takes place specifically at the roost site (Air Force 2001). Service and Government of Guam wildlife biologists and authorized researchers are permitted access to the area and to the colony to monitor and conduct research on fruit bats. Similarly, the U.S. Navy (Navy) and the Service restrict access to their lands, which include native forest that provides foraging habitat for the fruit bat.

The remaining roost site is managed as part of the Guam National Wildlife Refuge (Refuge) overlay under a cooperative agreement with the Air Force. The Refuge was created on October 1, 1993, with additional lands (overlay portion) incorporated in 1994 by cooperative agreements between the

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Service, the Air Force and the Navy. The establishment and management of the overlay portion of the Refuge on Navy and Air Force lands provides a commitment by the three agencies to develop coordinated programs centered on the protection of endangered and threatened species and other native flora and fauna. Active implementation of such programs by these agencies contributes to the continued survival of the Mariana fruit bat on Guam, as important foraging and roosting habitat is located within the Refuge boundaries. However, the lack of brown treesnake control in the immediate area where the fruit bats roost is a serious deficiency in existing programs to protect endangered species on the overlay refuge.

There is no U.S. Government-owned land in the CNMI, but the Navy leases Farallon de Medinilla and part of Tinian. All other public lands are administered by the CNMI government. Saipan has little public land that is not leased and developed, but a few areas still support native forest that is occasionally used by fruit bats. Tinian has large tracts of public land that contain small stands of native forest suitable for bats, and a large portion of public land on the northern end of the island is under lease to the Navy for military activities (Lusk et al. 1997). All of Aguiguan is owned by the CNMI government. Approximately 60 percent of the land on Rota is publicly owned, although much of this has been leased to private individuals. The primary roosting areas on Rota are on Commonwealth lands, but some private lands still retain native limestone forest that may support fruit bats. The northern islands are mostly public lands, with some land developed as small homestead lots.

Population Surveys and Status

Obtaining accurate estimates of fruit bat populations in Pacific archipelagos depends on regular monitoring, standardized survey methods, and consideration of the unique ecology and physiographic environment of bat populations in various island groups (Utzurrum et al. 2004). The difficult terrain of the Mariana Islands, remote location of the northern islands of the CNMI, and the high costs associated with transits of the island group by sea and aerial surveys of individual islands have hindered the establishment of a standard monitoring program for the archipelago.

No known historical records exist to document the status of the Mariana fruit bat prior to the 20th century. The history of fruit bat surveys and changes in numbers summarized below represent a variety of methods and analyses. Archipelago-wide surveys were conducted in 1983 (Wiles et al. 1989) and 2001 (Johnson 2001).

The relatively isolated northern islands support the majority of the fruit bats in the archipelago, but because of their remote location, these islands have not been surveyed as frequently as the southern islands. Individual surveys have been conducted on several of the southern islands at relatively frequent intervals, and comprehensive surveys of the northern islands were conducted in 1983, 2000, and 2001 (Wiles et al. 1989; Cruz et al. 2000a-f; Johnson 2001). Opportunistic surveys have also occurred sporadically throughout the archipelago. The methods used in the northern islands in 2001 were significantly different from those used in 1983 and 2000; we therefore consider only Wiles et al. (1989) and Cruz et al. (2000a-f) for purposes of comparison (Table 1). A conservative interpretation of this comparison indicates a decline between 1983 and 2000, especially on the two islands that supported the largest numbers of fruit bats in the archipelago 20 years ago (Table 1).

Two of the northern islands are not included in this table: Uracas, the most northerly, where fruit bats are not known to occur; and Farallon de Medinilla, where fruit bats have been observed on only one occasion. See text and Table 2 for information about additional and more recent surveys and observations of fruit bats on the southern islands of the CNMI and Guam, and on Farallon de Medinilla, Anatahan, Sarigan, and Pagan.

Table 1.--Summary of Mariana Fruit Bat Survey Results: Minimum Estimates

Island

Area Sq. mi (Sq. km)

1983 \1\

2000 \2\

Maug.................................. 0.8 (2.0)