Technical note usda natural resources conservation service pacific islands area

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Obstacles to flight. Obstacles during flight are a major source of mortality for some continental species, particularly during mass migrations. Major sources of mortality include windfarms for migratory tree-roosting bats like the North American hoary bat (25) and barbed wire fences for some migratory bats in Australia (26). Hawaiian hoary bats are not known to migrate in large aggregations. Nevertheless, a small number of individuals have been documented colliding with obstacles (e.g., wall, vehicle, windmill, barbed wire fence), presumably while foraging (2).

Dr. Ben Okimoto monitors the health of a Hawaiian hoary bat with an injured wing (Photo Honolulu Zoo).

ntroduced predators.
Young Hawaiian hoary bats may be vulnerable to cats, rats, and other predators during rearing and fledging periods. On Aguiguan, rats and monitor lizards are potential predators of Pacific sheath-tailed bats, and brown tree snakes would be a threat if they reached the island (20).
Pesticides. Insecticides can affect the abundance of insect prey available to Hawaiian hoary bats and Pacific sheath-tailed bats through reduction in insect populations or insect habitat, and may cause bats to fly further in search of food or feed in unfamiliar landscapes. Some insecticides can also affect bats through bioaccumulation of chemicals through the food chain. Herbicides can alter vegetation structure and community composition in foraging habitats, likely influencing the availability of insect prey.

‘Ōpe‘ape‘a skeletal specimen (Photo P.Q. Tomich).

atural phenomena.
Natural phenomena can become a factor in species decline for populations already in danger of local extinction. In Guam, CNMI, and American Samoa, typhoons/hurricanes can cause flooding of seaside caves and potentially damage food resources of Pacific sheath-tailed bats. Although storms typically last only a day, storm surges, flooding, tree defoliation, and insect depletions associated with severe storms have longer term effects (22). In American Samoa, coastal caves are small, shallow, and vulnerable to tidal surges (19).


Habitat component

Habitat characteristics

 Hawaiian hoary bat

 Pacific sheath-tailed bat


  • Moths, beetles, termites, leafhoppers, flies, bugs and other night-flying insects

  • Small night-flying insects

Cover (foraging)

  • Open, wooded, and linear habitats

  • Forest edges and gaps, croplands with structural diversity

  • All elevations

  • Native and nonnative forests

  • Forages in forest understory, also in and above upper canopy

Cover (roosting)

  • Roosts in caves and other cavities

  • Human and ungulate disturbance minimal


  • Foods presumably provide adequate water in diet

  • Forage over wetland, riparian, and coastal-marine habitats

  • Foods presumably provide adequate water in diet


  • Suitable roosting habitat near insect-rich foraging habitats

  • Suitable roosting habitat near insect-rich foraging habitats.

Minimum habitat area

  • Wide ranging species

  • Average home range is 124 ac (50 ha) for males on a macadamia nut farm, varies by habitat type, territories may overlap

  • Home range unknown

Potential threats

  • Roost disturbance

  • Loss of habitat

  • Obstacles to flight

  • Introduced predators

  • Pesticides

  • Natural phenomena (e.g., severe storms)

  • Roost disturbance

  • Loss of habitat

  • Obstacles to flight

  • Introduced predators

  • Pesticides

  • Natural phenomena (e.g., severe storms, tidal surges)

Using the habitat characteristics above, subjectively rate the (a) availability and quality of bat habitat and (b) presence or absence of potential threats within a planning area. Habitat components rated “low” or “absent” or potential threats rated “present” could be limiting habitat quality.

(a) Habitat component

Quality / Availability






Cover (foraging)

Cover (roosting)



Minimum habitat area

(b) Potential threat



Roost disturbance

Loss of habitat

Obstacles to flight

Introduced predators


Natural phenomena

Management treatments should address the habitat components and potential threats that appear to limit habitat potential for bats. Specific management options are lacking for both species. Thus, general advice for insectivorous bats is given below that may increase the quality or availability of each habitat component. NRCS Conservation Practices and various programs that may provide financial or technical assistance to carry out practices are also listed.

Habitat component

General management options for increasing habitat quality or availability

Conservation Practices


  • Minimize adverse effects of pesticides on non-target species (i.e., reduction in prey and prey habitat) by developing an integrated pest management plan; include role of bats and other native species in reducing pest outbreaks

595, 645

Cover (foraging)
If insectivorous bats are known or suspected to be foraging in area:

  • In native forest, protect and enhance habitat especially mature trees and understory; restore new forest patches

  • Restore forest community structure and function to benefit multiple species of native birds and bats

  • Consult with NRCS Biologist, Forest Ecologist, or Plant Materials Center for best plant sources, spacing, care, and maintenance (See Appendix A for native plants used by Hawaiian hoary bat)

  • For Island of Hawai‘i, see NRCS Ecological Site Descriptions for your planning area:

314, 382, 550, 612, 643, 645

  • In orchards, increase horizontal and vertical vegetative structure by enhancing windbreaks; plant multi-species, tree-shrub windbreaks with varied leaf forms; use native species when feasible

380, 612, 645, 650

  • In tree plantations, avoid extensive clearcuts; integrate selective harvest techniques that leave young trees and snags; create gaps, bays, or irregular forest edges

645, 666

  • Leave snags (dead or dying trees) and downed wood; old trees and decomposing woody debris provide good habitat for insects and other organisms eaten by bats

643, 645

  • Exclude feral ungulates through fencing or control feral ungulate populations through trapping or hunting

382, 645

Cover (roosting)
If insectivorous bats are known or suspected to be roosting in area:

  • Protect roost sites and surrounding habitat by excluding areas from or minimizing activities related to resource extraction, grazing, or vehicular traffic

Hawaiian hoary bat:

  • Minimize chances of negatively impacting roosting bats by conducting activities such as vegetation clearing or timber harvesting when bats are not or not likely to be present

  • In windward Hawai‘i, bats are not likely to be present Jan-Apr in lowlands and Jun-Nov in highlands (>5250 ft [1600 m] elevation)

Pacific sheath-tailed bat:

  • Control feral ungulate access to caves through fencing, gating, trapping, or hunting

  • Control human access to caves through gating and signage

382, 472, 528, 595, 645

  • Protect roost sites and surrounding habitat from potential predators

Hawaiian hoary bat:

  • Keep cats and dogs restrained and away from bat roost sites, particularly during breeding

  • Hawaiian hoary bats bear young May-Aug and fledge pups Jul-Sep which is the most critical time (see pg. 3)

Pacific sheath-tailed bat:

  • If rats or monitor lizards are suspected predators, control them through trapping or other wildlife agency approved methods

382, 595, 645

General advice to conserve and enhance insect diversity for bats

  • If river bank management (e.g., dredging) is necessary, restrict management to small areas or one bank at a time; protect habitat by retaining natural meanders, shallow pools and riffles, and bankside trees and shrubs

391, 395

  • Establish riparian buffer zones through fencing, managing roads, runoff, feral ungulates, livestock, and vegetation (for large properties, conduct a watershed analysis to identify and halt or control activities contributing to habitat degradation)

382, 390, 391, 395, 528, 560, 578, 614

  • Protect and enhance wetlands; including small temporary pool complexes with varied depths, aquatic vegetation, and high insect diversity

644, 646, 659

  • Avoid introducing nonnative fish to water bodies; fish can deplete aquatic insect communities and degrade water quality

644, 646

Interspersion and minimum habitat area

  • Consider relationship of planning area to habitat components on property or neighboring lands. Landowners can manage for bats if one of more of the habitat components is present on their property and adjacent lands provide other habitat components.


Fencing considerations

Options to prevent potential bat entanglement in barbed wire fences:

  • Replace top 2 strands with smooth high-tensile wire

  • Omit barbed wire atop hogwire fences

  • Install a 6-ft (1.8-m) high hogwire fence without barbed wire on top

  • Remove fence if old or no longer needed

382, 645

NRCS Conservation Practices: 314 Brush Management, 380 Windbreak/Shelterbelt Establishment, 382 Fence, 390 Riparian Herbaceous Cover, 391 Riparian Forest Buffer, 395 Stream Habitat Improvement and Management, 472 Access Control, 528 Prescribed Grazing, 550 Range Planting, 560 Access Road, 578 Stream Crossing, 595 Pest Management, 612 Tree/Shrub Establishment, 614 Watering Facility, 643 Restoration and Management of Rare or Declining Habitats, 644 Wetland Wildlife Habitat Management, 645 Upland Wildlife Habitat Management, 646 Shallow Water Management for Wildlife, 659 Wetland Enhancement, 650 Windbreak/Shelterbelt Renovation, 666 Forest Stand Improvement (More info:
NRCS Conservation Programs that apply: CREP Conservation Reserve Enhancement Program (Hawai‘i only - administered by Farm Service Agency); CSP Conservation Stewardship Program; EQIP Environmental Quality Incentives Program; WHIP Wildlife Habitat Incentives Program; WRP Wetlands Reserve Program (More info:


Federal – Threatened

Guam – Endangered

CNMI – Threatened/Endangered

Species Profile

Mariana fruit bat, fanihi, pai‘scheei

Photo © Merlin D. Tuttle, Bat Conservation International

Scientific name: Pteropus mariannus

Habit: Colonial, nocturnal

Wingspan: 34 - 43 inches (86 -108.5 cm)

Weight: 0.73 - 1.37 lbs (330 - 620 g)

Range: Micronesia, formerly Ryukyu Islands

Breeding period: Year-round

No. of pups per year: Usually 1

Roosting habitat: Primarily native forests

Foraging habitat: Forests, farmlands, and coastal strand

Food habits: Frugivorous - eats primarily fruit, also nectar, pollen, flowers, and leaves

Population estimate: 5000 (Marianas)

The Mariana fruit bat or fanihi is a medium-sized member of the ecologically important old world fruit bat family (Pteropodidae), which consists of bats that forage primarily on fruit, flowers, nectar, and pollen. It is a striking dark brown to black bat with a golden “cape” around its neck and back. On islands, fruit bats (also known as flying foxes) are often important seed dispersers, playing a critical role in plant reproduction, diversity, and distribution, including post-typhoon plant regeneration (27-29).
The species is known from the Caroline (Palau, Ulithi, Yap, Kosrae), Mariana, and formerly Ryukyu islands (6 subspecies). In the Marianas, it was once a common sight. On Guam, fanihi became less common in the 1930s-1940s, then plunged from about 3000 in the 1950s to <50 bats twenty years later. Today, there are an estimated 5000 bats in the CNMI and <100 on Guam (22). Overall, bat numbers in the southern and some northern islands in the chain are in decline, while numbers on some northern islands appear stable (30). Few fanihi survive on Saipan or Tinian. Colonies are believed to move infrequently between islands, probably in response to severe food limitations or colony disturbance (e.g., typhoons followed by poaching), which may explain sudden increases or decreases in bat numbers on individual islands (31). Historically, fanihi coexisted on Guam with little Mariana fruit bats, which are now extinct.
Fanihi are a traditional food source of the people in the Marianas. However, overhunting is a major cause in the bats’ decline, both in the past and presently. Fanihi are Federally-protected as a Threatened species throughout the Mariana Islands. Hunting is prohibited by law until fanihi populations can be restored to larger levels that may allow for sustainable harvests. Recent studies linking regular consumption of fanihi to a disease of the nervous system (known as lytico-bodig) in people on Guam suggest this practice may have negative health effects (32).
Fanihi breed year-round with no apparent seasonal peak. Females bare one pup at a time. Although unknown for fanihi, other fruit bats have a gestation period (pregnancy) of 4.5-6 months, and pups reach maturity between 6-18 months of age. Historically on Guam, the species roosted in large colonies (60-800 bats) made up of harems, bachelor groups, and solitary males. Harems consisted of 1 male to 2-15 females. On Sarigan (CNMI), there are more solitary bats and smaller colonies than on some of the larger islands in the chain (33).
Periods of breeding activity in fanihi (34)

















Pup births


Pup fledging

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