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Ranging Patterns and Habitat Use of a Solitary Flying Fox (Pteropusdasymallus) on Okinawa-jima Island, JapanAuthor(s): Atsushi Nakamoto , Kazumitsu Kinjo and Masako IzawaSource: Acta Chiropterologica, 14(2):387-399. 2012.Published By: Museum and Institute of Zoology, Polish Academy of SciencesDOI: http://dx.doi.org/10.3161/150811012X661701URL: http://www.bioone.org/doi/full/10.3161/150811012X661701

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INTRODUCTION

Roosting habits are one of the most important de-

termining factors for home range and movement

patterns in many chiropteran species (Kunz, 1982).

Most species exhibit coloniality and use caves as

fixed roosting sites, although a variety of roosting

types are known (e.g., tree hollow and tent making).

Several advantages are derived from living in large

colonies or using of caves, such as stability in tem-

perature and humidity levels or predator avoidance.

Flying foxes (genus Pteropus) also exhibit strong

coloniality and form large colonies that consist of

hundreds to over a million individuals in a tradition-

al roosting site, which is known as a camp (Pierson

and Rainey, 1992). The movement patterns of many

frugivores, such as flying foxes, commonly depend

on seasonal changes in food distribution and

availability due to fruiting phenology (Whitney and

Smith, 1998; Palmer et al., 2000; Hodgkison et al., 2004; Nakamoto et al., 2007b). Marshall (1983)

suggested that colonial roosting results in flock

foraging in the same feeding area or long-distance

commuting from a day roost to feeding sites because

local competition for food is higher around the

colony. Indeed, many Pteropus species commonly

commute long distances (20–50 km) from a day

roost to foraging sites (Marshall, 1983) and have

huge home ranges. The extents of the daily ranges of

individual bats may be strictly limited by their roost-

ing locations in colonial flying foxes such as camp-

making bats. On the other hand, only two species

(P. samoensis and probably P. pumilus) had been

known to be solitary flying foxes (Mickleburgh etal., 1992), until the recent addition of the Ryukyu

flying fox (P. dasymallus) to the list of solitary

species (Nakamoto, 2008). The foraging patterns of

these flying foxes are generally unknown because of

their rare social system among chiropterans.

The Ryukyu flying fox [body mass 350–600 g,

forearm length (FAL) 130–145 mm] inhabits the

Ryukyu Archipelago of Japan, Turtle Island and

Green Island of Taiwan, and small northern islands

of the Philippines. It is divided into five subspecies

Acta Chiropterologica, 14(2): 387–399, 2012PL ISSN 1508-1109 © Museum and Institute of Zoology PAS

doi: 10.3161/150811012X661701

Ranging patterns and habitat use of a solitary flying fox (Pteropus dasymallus) on

Okinawa-jima Island, Japan

ATSUSHI NAKAMOTO1, 3, KAZUMITSU KINJO2, and MASAKO IZAWA1

1Faculty of Science, University of the Ryukyus, 1 Senbaru, Nishihara, Okinawa, 903-0213, Japan2Faculty of Law, Okinawa International University, 2-6-1 Ginowan, Ginowan, Okinawa, 901-2701, Japan

3Corresponding author: E-mail: dasymallus@gmail.com

Most flying fox species (genus Pteropus) exhibit strong coloniality. They are highly mobile animals and commonly forage over vast

areas. Only a small number of species are solitary, and their foraging and roosting patterns are not well understood. Here, we

examined ranging patterns and habitat use of Orii’s flying fox, Pteropus dasymallus inopinatus, a solitary fruit bat, using radio-

tracking from April 2002 to January 2006 on Okinawa-jima Island, Ryukyu Archipelago, Japan. The daily home range size for this

species was very small (mean 52.5 ha) compared to other Pteropus species, although home range size was highly variable among

individuals and seasons. The distance between a day roost and feeding trees was 621 m on average, with a maximum of 6,875 m.

Day roost site shifted frequently (every 1.6 ± 0.8 days) to a nearby site in the current foraging area. The distance between consecutive

day roost sites was 792 m on average, with a maximum of 6,000 m. These bats favored forest habitats for roosting sites, whereas

they often used residential areas as feeding sites. Our results suggest that they regularly shifted the location of their personal activity

range, a small home range with roost switching, probably to track changes in food availability and to avoid local competition for

food. The solitary roosting system of this species links to its flexible foraging system, which likely provides an advantage for using

limited food resources on a small island, even when food is patchily distributed in urbanized habitats.

Key words: home range size, movements, Pteropus dasymallus inopinatus, radio-tracking, Ryukyu flying fox, roost switching, social

system, urbanization

according to island groups (Yoshiyuki, 1989; Hea -

ney et al., 1998; Kinjo and Nakamoto, 2009). This

species is listed as a Near Threatened animal in the

IUCN red list (Heaney et al., 2008). Recently, it was

found that the Ryukyu flying fox is solitary both

when roosting during the day and when foraging at

night (Naka moto, 2008), although it occasional-

ly roosts in small groups, usually in the foliage of

canopy layers of tall trees. It consumes a wide

variety of food items, feeding on over 120 plant spe -

cies, including fruits and nectar, along with occa-

sional leaves and insects (Funakoshi et al., 1993;

Nakamoto et al., 2007a; Lee et al., 2009). Its mating

season occurs mainly from September to December

and females give birth to a single baby between

April and June (Kinjo and Nakamoto, 2009).

A subspecies of P. dasymallus, Orii’s flying fox,

P. d. ino pinatus, is endemic to the Okinawa Islands

and is found in several types of habitats, including

forests, residential areas, and plantations. This taxon

obtains stable food resources by having a broad diet

and through the intensive use of planted trees de-

spite the limited food resources that are generally

available on small subtropical islands that experi-

ence unexpected food shortages because of typhoons

(Na kamoto et al., 2007b). There are no crucial pred-

ators for flying foxes on the Okinawa islands.

We anticipated that the solitary flying fox

P. d. inopinatus would have a unique foraging sys-

tem that differed from that of colonial Pteropusspecies. On the basis of the aforementioned spatial

constraints in relationships between roosting sites

and foraging ranges, we hypothesized that (1) a soli-

tary Orii’s flying fox would use a number of roost-

ing sites, and (2) individuals would regularly change

their home ranges to avoid local competition for

food.

MATERIALS AND METHODS

Study Area

Okinawa-jima Island (approximately 1,200 km2) is located

in the central part of the Ryukyu Archipelago, Japan (26°12’N,

127°41’E) and is on the northern limit of the range of the fami-

ly Pteropodidae. Its climate is subtropical, with an average an-

nual temperature of about 23.0°C and average annual precipita-

tion of more than 2,000 mm. The vegetation and topography dif-

fer between the northern and south-central regions of the island.

Most of the northern area is mountainous (elevation ≥ 400 m

a.s.l.) and continuously covered by non-limestone evergreen

forests that are dominated by Castanopsis sieboldii and Schi-ma wallichii liukiuensis, which are commonly called ‘Yanbaru

forests’. The south-central region is hilly (elevation ≤ 200 m

a.s.l.) and is largely covered by residential areas and sugarcane

plantations (Fig. 1); it contains remnant patches of limestone

evergreen forests that are typically composed of Lauraceae and

Ficus spp. (Miyawaki. 1989). On Okinawa-jima Island, Ficusspp. are the main food resources of P. d. ino pinatus (Naka moto

et al., 2007b), and these plants are abundant in limestone

forests, but not in non-limestone forests. Approximately 1.13

million people (about 80% of the total population of the island)

live in the south-central region, and the human density is very

high (2,354 persons/km2). In the south-central region, many

food trees have been planted in school gardens or urban parks

(e.g., Ficus microcarpa, Terminalia catappa, and Erythrina ori-entalis). On average, 7.4 typhoons strike Okinawa Prefecture

per year (1981–2010 data base from the Japan Meteorological

Agency), and these storms often affect the availability of food

resources for bats.

Capturing and Radio-tracking

Radio-tracking surveys were conducted in two different

habitat types: urban habitats in the south-central region and con-

tinuous forest habitats (Yanbaru forests) in the northern region

of Okinawa-jima Island. The surveys were conducted from

April 2002 to January 2006 to determine the home range size

and habitat use of flying foxes. In total, 20 foraging flying

foxes [11 individuals on the campus of the University of the

Ryukyus (UR) and nine individuals in the Yanbaru forest area

(YF)] were captured using hand nets or mist-nets. For each bat,

we recorded forearm length, body mass, sex, age class, and

reproductive status. Age classes were categorized into two

classes (i.e., adult and subadult) based on body size and repro-

ductive maturity. The subadult period was defined as the time

from independence up to three years old and adults were more

than three years old, by which time they had developed and

reached full size. The following reproductive characteristics

were also used as a standard indicator of age class. Adult males

had orange or yellowish collars of fur and large testis (≥ 15

mm), and subadult males had brown collars and small testis

(< 15 mm). Adult females (parous) had large (5–10 mm) and

blackened nipples, and subadult females (nulliparous) had small

(ca. 2 mm) and non-blackened nipples. Within the subadult cat-

egory, both sexes were pooled for analysis. Each flying fox had

an identifiable microchip inserted under the skin (Surge

Miyawaki Co., Ltd. [Trovan, Ltd.], Tokyo, Japan), and radio

transmitters (Model A2830 or A2850; ATS Inc., Isanti, Minne -

sota, U.S.A., and Architech Inc., Tokyo, Japan) fixed on leather

collars with reflective tape or handmade transmitters (10–15 g

including the collar, less than 3% of body weight) were at-

tached. After an animal was processed, it was released at the

capture site. During one tracking session, each radio-collared

individual was tracked for four or five consecutive nights using

the receivers (FT-690 mkII, Yaesu Musen Co. Ltd, Sapporo,

Japan) and a two-element Yagi antenna (Architech Inc., Tokyo,

Japan) with the observer traveling by car or on foot. Two track-

ing methods, the homing method (Mech, 1983) and the triangu-

lation method (White and Garroto, 1990), were used. In the

homing method, tracking was conducted continuously from the

day roost to the next day roost. In most cases, the locations and

behaviours of radio-collared bats were visually observed using

a hand light, binoculars, and a spotting scope, and the food

items used and the amount of time spent in each tree were re -

corded. Day roost sites were located at the start and end of night

tracking, and they were also checked at noon. When using the

triangulation method, the location of an animal was determined

388 A. Nakamoto, K. Kinjo, and M. Izawa

every 1–2 hours. The locations of all trees used were recorded

on a map (1:10,000) or marked with GPS and entered into

ArcGIS 8.2 (ESRI Inc.). When a radio-collared animal was lost

over three hour period in total during one night tracking, the

data for that night were omitted from the analysis (22/124 track-

ing days). Consequently, data from a total of 30 tracking ses-

sions (102 tracking days) were used in the following analysis

(Table 1).

Analysis of Home Ranges

Because of their nomadic behaviour, as described later, the

home range size of P. dasymallus may never reach a pla teau.

Therefore, we calculated the home range size as a daily unit.

Daily home range size (DHR) was defined as the minimum con-

vex polygon (100% MCP) that contained all of the trees used,

including day roost trees, during one day. Daily foraging area

(DFA) was defined as the 100% MCP that contained all of the

feeding trees used in one night. Daily movement distance

(DMD) was defined as the sum of the straight line distances be-

tween consecutive trees in the order that the bat used them dur-

ing one night. Roost fidelity (RF) was defined as the number of

tracking days/the number of roost sites used.

Analysis of Habitat Use

For the analysis of habitat use for roosting and feeding sites,

we only used data for the flying foxes that were captured at UR

and that were tracked using the homing method (nine bats, 42

tracking days) because all location points for flying foxes

caught in YF occurred in the forest habitat type. GIS vegeta-

tion data from the Japan Integrated Biodiversity Information

Ranging patterns and habitat use of Pteropus dasymallus 389

FIG. 1. Map of habitat types in the south-central region of Okinawa-jima Island. UR: the campus of the University of the Ryukyus

(see text for details of habitat types)

5 km

PacificOcean

East China

Sea

NN

UR

residential area

grassland

plantation

forest

others

5 km

UR

YF

Capture FAL BW Tracking DHR (ha)Bat ID site

Age Sex(mm) (g) period days method 0 ± SD min.–max.

115 UR Ad M 136.9 420 Apr-02 3 H 103.0 ± 21.2 90.3–127.4

115 UR Ad M May-02 3 H 112.5 ± 103.2 3.9–209.2

117 UR Ad M 137.8 478 Jul-02 4 H 5.1 ± 0.9 4.1–6.1

117 UR Ad M Aug-02 3 H 8.2 ± 1.7 6.2–9.2

121 UR Ad M 136.1 418 Sep-02 4 H 34.0 ± 19.8 7.6–50.3

123 UR Ad Fa 134.4 568 Nov-02 4 H 8.2 ± 13.3 0.3–28.1

116 UR Ad Fa 140.4 518 Apr-03 3 H 217.0 ± 83.8 120.5–271.6

116 UR Ad Fb May-03 3 H 11.4 ± 8.3 2.2–18.4

133 UR Ad M 138.7 498 Aug-03 4 H 140.3 ± 159.6 29.9–376.7

135 YF SA F 133.5 360 Aug-03 1 T 85.7 85.7–85.7

129 UR SA F 137.3 378 Sep-03 4 T 9.3 ± 6.7 2.2–15.8

130 UR Ad M 137.9 423 Sep-03 4 T 58.6 ± 51.4 8.7–116.9

133 UR Ad M Sep-03 4 T 22.8 ± 14.4 4.3–37.0

135 YF SA F Sep-03 4 T 196.0 ± 96.3 63.6–294.5

129 UR SA F Nov-03 4 T 2.9 ± 0.5 2.3–3.4

56 UR Ad M 137.5 393 Nov-03 4 T 0.5 ± 0.5 <0.1–1.2

56 UR Ad M Nov-03 1 H 5.4 5.4–5.4

56 UR Ad M Dec-03 4 H 12.1 ± 4.3 7.3–16.3

141 YF Ad M 140.0 458 Dec-03 3 T 46.4 ± 53.4 1.1–105.2

142 UR SA F 129.7 353 Feb-04 2 H 4.9 ± 2.7 3.0–6.9

143 YF SA F 120.8 298 Mar-04 – T – –

144 YF SA M 127.7 343 Jun-04 3 T 15.5 ± 21.9 0.7–40.6

145 YF Ad F 135.8 363 Jul-04 4 T 10.4 ± 6.5 5.4–19.9

146 YF Ad M 134.6 488 Jul-04 4 T 4.9 ± 4.1 1.2–10.6

148 YF Ad M 134.2 470 Oct-04 4 H 1.6 ± 1.5 0.5–3.8

149 YF Ad F 133.9 560 Oct-04 3 T 1.2 ± 1.0 0.2–2.2

148 YF Ad M Dec-04 4 H 2.6 ± 1.3 1.2–4.0

149 YF Ad F Dec-04 4 T 0.7 ± 0.2 0.5–1.0

151 YF SA F 126.6 295 Jan-05 2 H 56.8 ± 13.7 47.0–66.5

151 YF SA F Mar-05 4 T 2.2 ± 1.2 0.8–3.7

179 UR SA M 133.1 435 Jan-06 4 H 395.7 ± 167.5 181.3–590.6

a — pregnant female, b — female with a baby

System, Biodiversity Center, were used to assess habitat type.

We rearranged these vegetation types to fit the vegetation types

used by flying foxes as follows: Forest — Psychotria manillen-sis-Acer oblongum community and exotic broad-leaf foresta-

tion; Grassland — Imperata cylindrical-Miscanthus sinensiscom munity; Residential area — residential area, artificial grass-

land, reclaimed land, and industrial area; and Plantation —

plantation (Fig. 1). UR was mostly covered by a Bischofia ja -vanica community, and this vegetation type was treated as

a park-like habitat. For foraging site selection, the percentage of

use for each habitat type was assessed based on the durations of

a bat’s visits to feeding trees. These values directly represent bat

habitat selection because all of the radio-collared bats had high

mobility and were capable of using all of the habitat types with-

in a 10 minute period. For roost site selection, the percentage of

use for each habitat type was assessed based on the number of

days the habitat was used by bats.

Statistical Analysis

We classified the study sites into two groups (UR and YF),

bat status into three groups (adult male, adult female, and

sub adult), and season into four groups (spring [March–May],

summer [June–August], autumn [September–November], and

winter [December–February]). To explore the effects of these

three variables on DHR, we used a generalized linear model

(GLM) with forward stepwise variable selection based on Akai -

ke’s information criterion (AIC). In the analyses of the three char-

acteristics of home range (i.e., DHR, RF, and DDR), we used

a Wilcoxon rank sum test to examine differences between study

sites, and a Kruskal-Wallis test to examine differences among

bat status and among seasons. All statistical analyses were con-

ducted using R 2.11.0 (R Core Development Team, 2011).

RESULTS

Home Range Size and Movements

The DHR (0 ± SD) of Orii’s flying fox was very

small (52.5 ± 87.3 ha, n = 30 tracking sessions) for

a Pteropus species, but it was highly variable among

individuals and tracking sessions (n = 102 tracking

390 A. Nakamoto, K. Kinjo, and M. Izawa

TABLE 1. Characteristics and variations in the home range sizes of radio-collared flying foxes (P. d. inopinatus) on Okinawa-jima

Island. Capture site: UR — University of the Ryukyus, YF — Yanbaru forest area; age: Ad — adult, SA — subadult; sex: M — male,

F — female; FAL — forearm length, BW — body mass; tracking method: H — homing, T — trianguration, DHR — daily home

range size

days, range: < 0.1–590.6 ha — Table 1). The GLM

analysis indicated that the DHR of Orii’s flying fox

could not be predicted using any or all of the vari-

ables (Table 2). Significant difference in DHR were

not found between the study sites (Wilcoxon rank

sum test, W = 137.5, n = 30, P = 0.22), although

DHR tended to be larger in UR than in YF (Table 3).

Similarly, significant differences in DHR were not

found among bat status categories (Kruskal-Wallis

[K-W] test, χ2 = 0.93, d.f. = 2, P = 0.62) or among

seasons (K-W test, χ2 = 2.43, d.f. = 3, P = 0.49), al-

though DHR tended to be larger in subadults than in

adults (Table 3). DMD was 3.5 ± 2.9 km (n = 30,

range: 0.1–13.9 km), and DFA was 28.6 ± 53.6 ha

(n = 30, range: 0.0–381.8 ha). The distance between

the day roost and feeding trees was 621 ± 849 m

(n = 481, range 0–6,875 m, median 277 m). Feeding

trees within 500 and 3,000 m of the day roost ac-

counted for 65.9% and 98.5% of all feeding trees,

respectively (Fig. 2a). The longest axis for the daily

home range was 1.2 ± 1.2 km (n = 30). Day roost

sites changed every 1.6 ± 0.8 days (n = 31), but RF

did not differ between the study sites (Wilcoxon

rank sum test, W = 112.0, n = 30, P = 0.88), among

bat status categories (K-W test, χ2 = 1.47, d.f. = 2,

P = 0.48), or among seasons (K-W test, χ2 = 2.97,

d.f. = 3, P = 0.40). The distance between consecu-

tive day roost sites (DDR) was 792 ± 1,181 m

(n = 74, range 10–6,000 m; median 336 m), and

63.5% and 95.9% of the day roosts were located

Ranging patterns and habitat use of Pteropus dasymallus 391

within 500 and 3,000 m of the previous day roost,

respectively (Fig. 2b). For DDR, significant differ-

ences were not found between the study sites

(Wilcoxon rank sum test, W = 103.0, n = 30,

P = 0.85) or among bat status categories (K-W test,

χ2 = 2.08, d.f. = 2, P = 0.35), although DDR tended

to be larger in subadults than in adults (Table 4).

Significant differences in DDR were not found

among seasons (K-W test, χ2 = 4.60 d.f. = 3,

P = 0.20), although DDR values in spring and win-

ter tended to be larger than in the other seasons

(Table 4).

Habitat Use

The campus of the University of the Ryukyus

and plantation environments were consistently used

as feeding sites throughout the year (Fig. 3a). Grass -

lands were scarcely used in every season. The per-

centage of use for residential areas was higher in

spring and summer. We often observed bats feed-

ing on fruits of Myrica rubra, Garcinia subellipticaor Psidium guajava in house gardens. In autumn,

the percentage of forest use was highest and residen-

tial areas were not used. We often observed bats

feeding on fruits of Morus australis in forest rem-

nants. In winter, all habitat types except for grass-

lands were used equally. Obvious seasonality in

the selection of roost sites was not found. The cam-

pus and forests each accounted for one-third of

the percentage of habitat use for roosting, where-

as residential areas were never used as roost sites

(Fig. 3b).

Ranging Patterns

The home range of Orii’s flying fox was divided

into the following three patterns based on its struc-

ture and stability over tracking sessions. These three

ranging patterns were observed in both study sites

and among all bat status categories. The first is the

‘Resident pattern.’ This is characterized as being ofFIG. 2. Distances between (a) day roosts and feeding trees

(n = 481) and between (b) consecutive day roosts (n = 74)

b

0 1 2 3 4 5 6 70

10

20

30

0 1 2 3 4 5 6 70

50

100

150

200 a

TABLE 2. Results of generalized linear model (GLM) with

forward stepwise variable selection based on Akaike’s

information criterion (AIC). Study site: UR and YF; bats’ status:

adult male, adult female, and subadult; season: spring, summer,

autumn, and winter

Step Variables Deviation AIC

1 (intercept) 221058 356.3

2 study site 215143 357.5

3 study site + bats’ status 207050 358.6

4 study site + bats’ status + season 204567 362.1

Distance (km)

Fre

quency

small size with daily ranges that overlap. For in-

stance, a subadult female (Bat ID 142) consistently

used the same foraging area within the campus in

a tracking session (Fig. 4a). The second is the

‘Split pattern.’ This is characterized as being of

medium-sized and includes two main foraging areas

that are near two different day roosts. For instance,

a sub adult female (Bat ID 151) used a foraging area

in the western end of its home range in the early

hours of 29 January 2005, later used another forag-

ing area in the eastern end of its home range that was

1.5 km from the previous foraging area, and then

switched to a roost site near the second foraging area

(Fig. 4b-1). The next night, this individual used the

foraging area in the eastern end of its home range in

the early hours of 30 January 2005; it later used the

foraging area in the western end of its home range

and then changed to a roosting site near the western

foraging area again (Fig. 4b-2). This pattern proba-

bly represents the process of shifting home ranges.

The third is the ‘Transient pattern.’ This is character-

ized as long-distance and continuous movements

over sev eral days that can occur without stable use

of a certain feeding area. For example, in the day-

time of 12 March 2004, a subadult female (Bat ID

143; the daily home range size of this bat was not

calculated due to partial tracking, see Table 1) was

found 4 km northeast from its capturing site on 22

Febru ary 2004 (Fig. 4c). She sequentially foraged

and moved northward on the same day, eventually

reaching the northern end of the island, which was 8

km away from the previous area. We were not able

to track her during the night of the 13 March, but we

392 A. Nakamoto, K. Kinjo, and M. Izawa

TABLE 3. Daily home range size (DHR, in ha) for Orii’s flying-foxes at two study sites on Okinawa-jima Island

DHR

Study area Adult male Adult female Subadult All

n 0 ± SD n 0 ± SD n 0 ± SD n 0 ± SD

UR 11 45.7 ± 50.4 3 78.8 ± 119.6 4 103.2 ± 195.0 18 64.0 ± 102.5

YF 4 13.9 ± 21.7 3 4.1 ± 5.5 5 71.2 ± 77.2 12 35.3 ± 57.6

All 15 37.2 ± 46.1 6 41.5 ± 86.1 9 85.4 ± 132.4 30 52.5 ± 87.3

TABLE 4. Distance between consecutive day roosts (DDR, in m) used by Orii's flying foxes on Okinawa-jima Island

DDR

Season Adult male Adult female Subadult All

n 0 ± SD n 0 ± SD n 0 ± SD n 0 ± SD

Spring 2 1335 ± 612 2 606 ± 472 1 167 5 810 ± 641

Summer 4 182 ± 154 1 61 2 1216 ± 1145 7 460 ± 706

Autumn 6 336 ± 458 2 32 ± 45 3 214 ± 255 11 247 ± 364

Winter 3 447 ± 645 1 109 3 1350 ± 1233 7 786 ± 969

All 15 450 ± 552 6 241 ± 354 9 810 ± 946 30 516 ± 678

found her the next day at a day roost site that was 4

km south of the northern end of the island. On 26

March, she was again found feeding near the cap-

ture site.

Range Shifts

The foraging pattern of a given individual

changed over time with changes in the three home

range patterns. In this section, we present changes in

the home ranges of two individuals as examples.

The above mentioned subadult female (Bat ID 151)

had the Split home range pattern in January 2005

(for details, see Fig. 4b), but her home range

changed to the Resident pattern, located at a point

6 km west of the previous area, during the next

tracking session in March (Fig. 5a). As another

example, on 3 June 2004, a feeding subadult female

(Bat ID 144) was found at a point approximately

20 km south of the site where she was captured on

25 May 2004 (Fig. 5b). The next day, she moved to

and roosted at a point approximately 6 km east. She

demonstrated the Resident home range pattern in

that area for five days, until the end of the tracking

session. We did not observe the details of her move-

ments from the day she was captured until 3 June.

However, we presumed that Bat ID 144 moved

continuously for 10 days because most of the roost-

ing sites of Orii’s flying foxes were located within

3 km of their previous day roosts (Fig. 2b). This

shows that Bat ID 144 had the Transient home

range pattern during a period of 10 days after being

captured. Thus, her home range changed from the

Transient pattern during the first 10 days to the Split

pattern on 3 June and to the Resident pattern from

4 to 8 June.

DISCUSSION

Compact Home Range of Solitary Fruit Bats

The home range size and total movement dis-

tance for Orii’s flying fox were markedly smaller

and shorter (52.5 ha and 3.5 km, respectively) than

those of other Pteropus species. For example, the

total movement distance of Pteropus alecto was

within 15.5–19.9 km (Palmer and Woinarski, 1999),

and P. vampyrus was found to have a huge home

range across multinational areas (Epstein et al.,2009). The extent of the range size for Orii’s flying

fox is similar to values for small-sized solitary roost-

ing pteropodids in the Old World (e.g., Winkelmann

et al., 2000, 2003; Bonaccorso et al., 2002, 2005)

and New World phyllostomids (e.g., Bonaccorso etal., 2007; Chaverri et al., 2007; Henry and Kalko,

2007). Orii’s flying fox is capable of flying at least

30 km across the sea (Nakamoto et al., 2011);

however, the present results indicate that they usual-

ly avoid long-distant flights. Their compact range

and foraging behaviour may be closely related to the

small amount of food that is available on the

small island, as was previously reported by Funa -

koshi et al. (2003). It seems likely that they would

avoid wasting energy during long-distance move-

ments. This foraging strategy may also allow each

bat to become familiar with concealed local food

resources (at the individual tree scale) within their

individual ranges.

Daily home range size varied considerably

among individuals and nights. Moreover, in the

analysis of three home range characteristics (i.e.,

DHR, RF, and DDR), there were no differences with

respect to bat status or season. These results may re-

flect differences in food conditions within the small

ranges of individuals. It is likely that other individ-

ual characteristics also influence home range size.

Subadults tended to have larger home ranges and to

Ranging patterns and habitat use of Pteropus dasymallus 393

0

20

40

60

80

100

Hab

itat

ty

pes

(%

) grassland

plantation

forest

UR

residential area

0

20

40

60

80

100

Spring Summer Autumn Winter All

Hab

itat

ty

pes

(%

)

a)

b)

FIG. 3. Percentages for habitat types used as (a) feeding sites and (b) roost sites by flying foxes captured on the campus in the south-

central region of Okinawa-jima Island. The percentages were based on the amount of time spent in each tree, and on the number of

days that a roost was used within each environment, respectively. UR: the campus of the University of the Ryukyus

travel longer distances between consecutive roost-

ing sites compared to adults. There are two possible

explanations for this pattern. First, subadults lack

experience and knowledge with food distributions.

An alternative explanation is that they are subordi-

nate to adults at feeding sites. Subadult Erabu flying

foxes P. d. dasymallus (Funakoshi et al., 2003) and

Tongan flying foxes P. tonganus (Banack and Grant,

2002) undertake long-distance movements while

searching for food.

Advantage of Spatial Flexibility

Bat activity ranges are restricted to the vicinity of

their roost site. If they can freely select the location

of their roost site, they can also forage freely. Soli -

tary social systems with non-colonial lifestyles, may

allow individuals to more flexibly in response to

changes in food conditions among their habitats. Orii’s

flying fox is a nomadic forager that uses the richest

foraging area according to its most recent local

394 A. Nakamoto, K. Kinjo, and M. Izawa

a N b-1 Na

29 Jan 2005

b-1

29 Jan 2005

c 12 Mar.

100 m 500 m

29 Jan 2005

b-2N

29 Jan 2005

N

13 Mar.

14 Mar.

3 Mar.

12 Mar.12 Mar.

30 Jan 200530 Jan 2005

26 Mar.

22 Feb.

12 Mar.

m3 k

Mar.

500 m

FIG. 4. Home range patterns for Orii’s flying fox. Daily home ranges are shown by minimum convex polygons (a, b). Stars indicate

day roost sites. whereas closed circles indicate feeding trees. a) Resident pattern. Home ranges of one subadult female (Bat ID 142)

during four days in February 2004. b-1, b-2) Split pattern. Home ranges of one subadult female (Bat ID 151) during two consecutive

days in January 2005. Dashed lines indicate ranges of 500 m from the day roost. c) Transient pattern. Home ranges of one subadult

female (Bat ID 143) observed from 22 February to 26 March 2004

experiences with food availability. They use suitable

foraging patterns that correspond to individual situ-

ations. For example, during food-rich periods, the

daily home range size might decrease and there may

be overlap among sequential days because of the re-

peated use of feeding trees (Resident pattern). On

the other hand, after the food resources in an area

become exhausted, bats undertake sudden long-dis-

tance movements to new locations to explore new

Ranging patterns and habitat use of Pteropus dasymallus 395

FIG. 5. Changes in home range patterns in Orii’s flying fox. a —

Day roost sites and feeding sites of one subadult female (Bat ID

151) from 1 January to 19 March 2005. The home range of this

individual changed from the Split pattern (details shown in Fig.

4b) to the Resident pattern; b — Day roost sites and feeding

sites of one subadult male (Bat ID 144) from 25 May to 8 June

2004. The home range of this individual changed from the

Transient pattern to the Split pattern and then to the Resident

pattern. Stars and circles indicate day roost trees and feeding

trees, respectively

3 km

Jan.2005Mar. 2005

Na

10 km

Capturing site

25 May

3 Jun.

4-8 Jun.

Transient pattern

Split pattern

Resident pattern

b

N

food resources (Split pattern). When an individual

cannot easily find new food resources during an ex-

tended period (e.g., food-scarce season), they move

continuously among locations to find new food re-

sources (Transient pattern). Each individual always

uses the foraging area with the most abundant food

resource, and the best area changes day to day with

the changes in food conditions. Similar nightly

movement paths (i.e., Consistency pattern, Shuttle

pattern, and Exploration pattern) have been reported

in Carollia perspicillata (Phyllostomidae), although

they use caves as roost sites (Heithaus and Fleming,

1978; Fleming and Heithaus, 1986; Fleming, 1988).

Many studies have shown that seasonal changes in

food abundance cause the seasonal migrations or

nomadism in pteropodids (Ratcliffe, 1932; Nelson,

1965; Thomas, 1983; Eby, 1991; Richter and Cum -

ming, 2006). Seasonal migrations may be advanta-

geous when there are predictable fluctuations in

food resources because of regular climate changes,

such as wet or dry seasons in the tropics. On the

other hand, a nomadic strategy may be effective

when unpredictable and frequent changes in

food resources occur, as has been observed in

the subtropics. Winkelmann et al. (2000) suggest-

ed there was a relationship between the solitary

roosting system and small home ranges on a radio-

tracking study of a solitary nectarivorous bat (Sy co -nycte ris australis), and Law (1993) suggested that

the flexible foraging system of this species may be

advantageous in subtropical and temperate areas.

This bat species also shows large variability in home

range size (12–1,796 ha) (Law and Lean, 1999). It is

important to note that this small-sized bat is nec-

tarivorous and requires high-energy food. The

Ryukyu flying fox is frugivorous, but it also needs

large amounts of food to maintain its large body

size. Chiropterans can probably freely adjust their

home range size using cost-effective flight move-

ments if they are not constrained by colonial habits

or roost site specialty. Con sequently, the roosting

sites of solitary species are not considered an impor-

tant factor determining the location of their home

range. Further studies of the relationships among

foraging behavior, food availability, and body size

are necessary to understand how roosting systems

affect foraging strategies.

Roost Switching and Food Exploration Model

Because Orii’s flying foxes individually roost in

tree canopies, they can frequently change their

roosting sites to reduce the distance between their

roost site and foraging areas. Obvious reductions in

commuting distance because of roosting site switch-

ing, excluding seasonal migration, have only been

reported in two solitary roosting pteropodids, Nycti -mene robinsoni (Spencer and Fleming, 1989) and

Pte nochirus jagori (Reiter and Curio, 2001), but

several authors have reported negative results from

roost switching (Morrison, 1980; Kunz, 1982; Win -

kel mann et al., 2000; Kunz and Lumsden, 2003).

Although our data were insufficient to discuss the

effectiveness of roost switching, after Orii’s flying

foxes changed roost sites, their commuting distance

was reduced in many cases.

Considering the distance between a day roost and

feeding trees, the pattern of roost switching and the

overlapping of home ranges can provide a model of

how Orii’s flying fox explores new feeding sites. It

appears that Orii’s flying fox used the following

two-stage foraging strategy to explore new food

resources. Individuals conducted most of their for-

aging activities within a 500 m radius of their day

roost and obtained additional food within a 3 km

radius of the roost (see Fig. 2a). When food condi-

tions decreased, they shifted the center of their for-

aging activity, including the roost site, to a new

food-rich area within the previous 3 km radius for-

aging area. This shift in home range can occur at

two different spatial scales (i.e., 500 m and 3 km ra-

dius from the day roost) (Fig. 6). This process of

shifting the activity range was termed the Split

home range pattern in this study. The shift in activi-

ty range may be caused by changes in the distri-

bution of food in the current home range. These

ideas were supported by the match between roost-

feeding site distance and roost-roost distance (Fig.

2a and 2b).

396 A. Nakamoto, K. Kinjo, and M. Izawa

FIG. 6. Shifts in the home range of one subadult male (Bat ID 179) from 17 January to 6 April 2006) in the south-central region of

Okinawa-jima Island. Stars indicate day roost sites. Solid circles and dashed-line circles indicate ranges less than 500 m and less than

3 km from a day roost, respectively

5 km

Pacific Ocean

East China Sea

N

26 Jan.

28 Jan.

29 Jan.

30 Jan.

22, 23, 27 Feb.

11 Mar.

6 Apr.

17-25, 27 Jan.

Habitat Selection and Conservation Implications

Radio-collared flying foxes intensively used

small areas on the university campus throughout the

year. This tendency corresponded with an increase

in the number of flying foxes which was determined

by a transect census on the campus (Nakamoto etal., 2007b). In urban areas, school gardens or urban

parks that contain many planted trees may play an

important role as feeding sites. Other habitats can be

used as a consequence of seasonal changes in the

main food resources (e.g., Myrica rubra and Gar -ci nia subelliptica in spring and summer in residen-

tial areas, Morus australis in autumn in forest areas,

and Terminalia catappa and Calophyllum inophyl-lum in winter on the campus). These results suggest

that habitat selection by Orii’s flying fox depends

directly on the availability of plant species, which

changes among seasons. It is also worth to noting

that this spe cies require a vast range throughout

their long life, which needs to be considered for their

conservation.

Fragmentation of natural habitats is one of the

most important factors causing species extinction

(Wilcox and Murphy, 1985). However, the degree of

adverse effects by fragmentations is different among

species (Cosson et al., 1999; Bianconi et al., 2006;

Willig et al., 2007). Orii’s flying fox uses a wide va-

riety of dietary items and exhibits spatial flexibility,

which allows it to survive in urbanized habitats.

Urbanization sometimes creates new food resources

for flying foxes, such as planted trees in urban parks

and along streets (McDonald-Madden et al., 2005;

Williams et al., 2006). However, for Orii’s flying

fox, remnant for ests in urban areas may be more

important as roosting sites, which serve as a base

point for their home range (i.e., the available forag-

ing range is restricted to the vicinity of the day

roost). Therefore, remnant forests are an important

habitat component for their conservation. For exam-

ple, the home ranges of Orii’s flying foxes in the

south-central urbanized area were twice as large as

those in the northern forest area, but the difference

was not statistically significant. Orii’s flying foxes

can use frag mented forests in urbanized areas be-

cause of their highly mobility, but additional defor-

estation may lead to reductions or disruptions of

urban populations.

ACKNOWLEDGEMENTS

We thank Professors M. Tsuchiya and A. Hagihara, Univer -

sity of the Ryukyus, for their valuable comments throughout our

study. We wish to thank to the Ministry of the Environment for

the permission to conduct the survey. Suggestions from anony-

mous referees were also very helpful in improving an earlier

version of this manuscript. This study was partially supported

by a Grant-in-Aid from Nippon Life Insurance Found ation,

Sasakawa Scientific Research Grand from the Japan Science

Society and the 21st Century COE program of the University of

the Ryukyus.

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