Pacific Science (1994), vol. 48, no. 2: 193-200© 1994 by University of Hawaii Press. All rights reserved

Distribution and Abundance of the Endangered Hawaiian Hoary Bat, Lasiuruscinereus semotus, on the Island of Hawai'i1

DAVID S. JACOBS2

ABSTRACT: The endangered Hawaiian hoary bat, Lasiurus cinereus semotus(H. Allen), has an island-wide distribution on the island of Hawai'i. However,abundance estimates suggest that its endangered status is appropriate. Althoughdistributed across wide ranges in elevation, temperature, and rainfall, this bat ismost often associated with native vegetation. Its diurnal and seasonal activitypatterns argue against migration within the island of Hawai'i. These patternssuggest that the Hawaiian bat uses more than one foraging site and that its useof foraging sites is influenced by changes in insect biomass.

THE HAWAIIAN HOARY BAT, Lasiurus cinereussemotus (H. Allen), is the only extant speciesof bat in the Hawaiian Archipelago. Althoughit has been on the endangered species list since1970 (Tomich 1986), no recovery plan exists.This is partly because very little is knownabout the natural history or the distributionand abundance of this bat. Information on itsdistribution is limited to reports of incidentalsightings on the island of Hawai'i (Baldwin1950, Bryan 1955, Tomich 1986) and Maui(Duvall and Gassman-Duvall 1991) or comesfrom surveys peripheral to surveys conductedfor forest birds (Kepler and Scott 1990). Theonly focused survey on the distribution andabundance of the Hawaiian hoary bat was anecholocation census conducted by J. H. Fullard(unpublished) on Kaua'i. The little that isknown about the distribution and abundanceof the Hawaiian hoary bat is confusing. Forexample, it is reported as both common(R. C. L. Perkins 1913, as cited in Baldwin1950) and rare (Baldwin 1950, Kepler andScott 1990) at higher elevations on the islandof Hawai'i.

The purpose of this study was to locateareas on the island of Hawai'i where bats

1 Manuscript accepted 8 April 1993.2 Department of Zoology, University of Hawaii at

Manoa, Honolulu, Hawai'i 96822. Current address:Department of Zoology, University of Cape Town,Rondebosch 7700, Cape Town, South Africa.

occurred regularly and to estimate the abun­dance of this bat in such areas. Both visualobservation and echolocation censuses wereused.

MATERIALS AND METHODS

The survey was undertaken on the islandof Hawai'i over a 3-yr period (1990 to 1992)for a total of 360 hr spread over 101 days. Batecholocation calls were monitored by drivingat speeds of 25-40 km hr-1 along roadsaccessible to two-wheel-drive vehicles (Figure1). The echolocation calls were monitoredusing a QMC Mini Bat Detector (QMC In­struments Ltd., 229 Mile End Road, LondonE1 4AA, England) tuned to a frequency of30 khz, which is the peak frequency of theHawaiian bat's echolocation calls (Belwoodand Fullard 1984). Each section of road wastraversed at least twice (once in each direc­tion) between 1830 and 2030 hr each night ofsurvey. Sections of road were surveyed on atleast two successive nights during Septemberand October of 1990. The direction that sur­veys were begun on successive nights wasreversed to reduce the effects of time of night.

Visual observations were also carried outat localities selected on the basis of the type ofhabitats in which bats were previously seenforaging (Tomich 1986; Hawaiian HeritageProgram, 1992, database of rare and endan­gered plants, animals, and natural communi-

193

194

ties of the Hawaiian islands, The NatureConservancy, Honolulu, Hawai'i.). Surveysat these sites commenced at dusk and lasteduntil dark, a period ofabout I hr. The numberof bats at each site was conservatively esti­mated by counting the maximum number ofbats that could be seen at anyone time.Counts were made every 10 min, and thelargest count in the hour of the survey wasrecorded. Because these bats dart in and outof foliage and one's field of view, they are notall visible at the same time.

Three of the sites (Kipahoehoe, Red Cin­der Road, and Ocean Vie~) Were also sur­veyed after dark using a bat detector. Duringthat time surveys were conducted every halfhour from 1900 to 2400 hr, and every hourfrom 2400 to 0600 hr, for two nights at thefirst two sites and six nights at Ocean View.When using the bat detector each detectionwas counted as a single bat. A fourth site(Wai'ono Ranch) was also surveyed from justbefore dawn to about 1 hr after sunrise, ontwo consecutive days.

Sites where bats were seen on the first nightwere surveyed again at least once. With theexception of Ocean View, which was surveyedfrom May 1991 to October 1992; Pohakuloa,which was surveyed from May to October1992; and Hawai'i Volcanoes National Park,which was surveyed in October 1992, all siteswere surveyed between September and Octo­ber 1990, and from February to August thefollowing year. The insect fauna at OceanView was sampled by means of a 22-wattultraviolet insect light trap (BioQuip Prod­ucts), from February to October 1992.

RESULTS

Visual Observation

Bats were seen at 16 of the 26 sites visited(Figure I). Two of the 16 sites were visitedonly once. These were located at Pu'uhonuao Honaunau Historical Park on the leewardcoast (maximum count of two bats in I hr ofvisual observation) and at the entrance tothe Kulani Correctional Facility (maximumcount of three bats in I hr of visual observa­tion) at the end of Stainback Highway. At the

PACIFIC SCIENCE, Volume 48, April 1994

remaining 14 sites, bats were observed on twoor more consecutive nights, during Septemberand October (Table I). They can therefore beregarded as sites used regularly by the bats (atleast at some times of the year [see TemporalPatterns]).

The largest number of bats seen in the hourfrom dusk to dark at each of the 14 sites is aconservative estimate (Table I). For example,at the Red Cinder Road site (at about the70-mile marker on Highway II), the maxi­mum number of bats observed was 5, but 12different individuals were captured at this siteover 14 trap nights.

In September 1990 I saw a total of 15 batsflying, singly or in pairs, upslope from belowHighway II over Kipahoehoe Natural AreaReserve and disappearing over the horizonhigh up the slope of Mauna Loa. Similarsightings have been made over the ManukaNatural Area Reserve about 10 miles (16 km)to the south of Kipahoehoe (Fujioka and Gon1988).

Echolocation Monitoring

Almost all of the bats detected by echoloca­tion monitoring were concentrated south ofKailua (Kona) between the 80- and 96-milemarkers along Highway II (Figure I). A totalof 18 bats (i.e., 18 detections) were detectedbetween the 80- and 96-mile markers over twonights of survey (4.25 ± 1.78 bats per tra­verse). Not a single observation or echoloca­tion detection was made in northwestern andsouthwestern Kohala on the leeward side ofthe Island. However, 40% of all bat sightingsoccurred on the drier leeward side of theIsland south of Kailua, compared with 26%on the wetter windward side.

Context ofObservations

ECOLOGICAL. The bats were all in flight andobviously foraging at the 16 sites where theywere seen. They displayed the darting, weav­ing flight, with sudden turns and dives, char­acteristic of foraging insectivorous bats thatcatch their prey on the wing. Bats detected(using the bat detector) along Highway IImay have been foraging as well. Visual obser-

Miloii

LEGEND

Echo Location Survey

0 No Bats

• Bats Seen

l), Bats Heard

N

i

FIGURE I. Distribution of Hawaiian hoary bat sightings and echolocation detections on the island of Hawai'i.Circles indicate 26 sites surveyed for bats: open circles indicate sites at which no bats were seen; closed circles indicatesites where bats were seen on at least two consecutive nights. Dashed lines indicate the roads along which echolocationsurveys were conducted; triangles indicate areas where bats were heard during the echolocation surveys.

196

TABLE I

NUMBERS OF BATS AT EACH FORAGING SITE ONTHE ISLAND OF HAWAI'I

% OF VISITSBATS WERE NO. OF NO. OF

LOCATION OBSERVED VISITS BATS

Kipiihoehoe Natural 100 5 10Area Reserve(Highway 11,90- to92-mile markers)

Manukii Natural Area 100 5 4Reserve (HighwayII, 80- to 82-milemarkers)

Red Cinder Road (off 77 13 5Highway II, near70-mile marker)

Highway II (70-mile 60 5 7-10marker)

Kaimii Bay (Puna) 100 2 3-4Kalapana (Puna, over 100 2 5

new lava flow)Kal6pii State Park 100 2 2

(Hiimiikua)Honoka'a (St. George's 100 5 2-3

Cemetery, LehuaStreet)

Waimanu Bay (North 100 2 5Kohala)

Ke6kea Bay (North 100 2 IIKohala)

Ocean View 100 6 4(intersection ofHukilau and TreeFern avenues, SouthKona)

P6hakuloa (Bradshaw 100 7 7-10Military Airfield)

Wai'ono Ranch 100 4 3-5(Kailua-Kona)

Hawai'i Volcanoes 100 2 2-3National Park

NOTE: Data are results of surveys conducted between Augustand October (see text).

vations offoraging bats before nightfall alongHighway II, especially those parts of the roadat or near Kipiihoehoe and Manukii NaturalArea Reserves, suggest that the bats detectedafter nightfall along this section of road mayhave been foraging as well.

The 15 bats observed flying over Kipii­hoehoe Natural Area Reserve in September

PACIFIC SCIENCE, Volume 48, April 1994

1990 appeared to be in transit. These batswere flying very high (> 150 m) and did notdisplay the darting and weaving flight charac­teristic of a foraging bat.

TEMPORAL PATTERNS. Diurnal activity pat­terns. The commencement and duration offoraging activity varied slightly from site tosite. For example, during September and Oc­tober (1990 and 1991) bats started foraging atRed Cinder Road at 1800 hr or immediatelythereafter. At the Ocean View and Kipiiho­ehoe sites, on the other hand, they first ap­peared between 1830 and 1845 hr. At the lattertwo sites the bats remained active until about0200 hr. There was, however, a peak in activ­ity just before sunset (four bats visible in thehour from dusk to dark), which droppedslightly as the night progressed (two batsdetected per hour). At Red Cinder Road,activity came to an almost complete stop atabout 1900 hr. In five nights ofsurveying, onlyone bat was detected briefly after 1900 hr-at2100 hr on two separate occasions. Pohakuloa(Bradshaw Military Airfield) was different inthat there did not appear to be a drop inactivity. The number of bats remained con­stant at least until 0230 hr when observationceased.

Early morning foraging was observed. Be­tween three and five bats were observed ontwo consecutive mornings foragingjust befored~wn and for at least 45 min after sunrise atWai'ono Ranch (Kailua-Kona). At Kipiiho­ehoe, the only other site at which bats wereobserved foraging at dawn, a single bat wasseen on one of the two mornings of sampling.Early morning foraging in bats has also beenreported on Maui (Duvall and Gassman­Duvall 1991).

Seasonal activity patterns. There appearedto be a drop in activity at most foraging sitesbetween February and August (Table 2). AtKipiihoehoe, Manukii, and Red Cinder Road,bat sightings dropped to three bats over threenights of sampling. Bats did not spend muchtime at these sites. Most of them made one tothree foraging circuits before disappearing. AtOcean View, sightings dropped to one batover four nights of sampling in February and

Hawaiian Hoary Bat on Island of Hawai'i-JAcoBs

TABLE 2

NUMBERS" OF BATS AT VARIOUS FORAGING SITES FOR DIFFERENT MONTHS

197

LOCATION FEBRUARY MAY

Ki"pahoehoe Natural Area Reserve 0.5 ± 0.5 0(2) (2)

Manuka Natural Area Reserve 0.5 ± 0.5 I ±O.O(2) (2)

Red Cinder Road 0.5 ± 0.5 0(2) (2)

Highway II (70-mile marker) 0 0(2) (2)

Kaimii Bay 0 0(2) (2)

Kal6pa State Park 0 0(2) (2)

Ke6kea Bay 0 0(2) (2)

Ocean View 0.25 ± 0.5 3.4 ± 0.5(4) (5)

P6hakuloa (Multipurpose Range 0.75 ± 0.5 0.2 ± 0.5Complex)' (4) (4)

JUNE

3.4 ± 0.5(2)

0.7 ± 1.0(4)

AUGUST SEPTEMBER OCTOBER

I 10 ± 0.0(I) (2)0 4 ± 0.0

(I) (2)0 5 ± 0.0 3.6 ± 2.2

(I) (2) (II)0 5.7 ± 2.6

(I) (2)0 3.5 ± 0.5

(I) (2)0 2 ± 0.0

(I) (2)0 II ± 0.0

(I) (2)5.6 ± 2.5 4.5 ± 1.7 3.5 ± 1.7

(4) (4) (2)0.5 ± 0.6 2.7 ± 2.1

(4) (4)

• Mean ± SD, sample size in parentheses.·See texl for year.'Data from Hawaiian Heritage Program database (see text).

to four bats over three nights of sampling inMarch. From May to August the numbers ofbats increased at this site and returned to theSeptember/October (1991) levels (Table 2),with the exception of a decrease in activityduring July and October (Figure 2). The dropin activity at Ocean View seems to be corre­lated with a drop in insect biomass (Figure 2).In the Multipurpose Range Complex of thePohakuloa Military Training Area, along theBobcat trail (1800 m elevation), between oneand three bats were seen and/or detected overa sampling period of four nights for eachmonth between February and August 1992(Table 2). This number increased to II batsover four sampling nights in August (Hawai­ian Heritage Program database). Incidentalsightings of bats at Hakalau Forest NationalWildlife Refuge (1890 m elevation) by JaanLepson (pers. comm.) followed the same pat­tern. Although bats were seen between Janu­ary and August, most sightings occurred fromSeptember to December. No bats were seen

or detected at any of the other sites betweenFebruary and August during the surveyreported here (Table 2). Bat numbers re­mained constant at Pohakuloa (BradshawMilitary Airfield) from May to October.

Environmental Correlates

HABITAT CHARACTERISTICS. The 14 forag­ing sites can be divided into four habitatcategories: native vegetation, exotic vegeta­tion, mixed (native and exotic) vegetation,and open ocean (Table 3). Of the 81 batsobserved at these sites (Table I), 44% wereassociated with native vegetation, 16% withexotic vegetation, 9% with mixed vegetation,and 25% foraged over open ocean. Bats weretherefore associated more with native vegeta­tion than with exotic vegetation, contrary towhat Kepler and Scott (1990) found.

TEMPERATURE. The foraging sites of theHawaiian bat extend over an elevational

6

5

c:Q)Q)

(/)4 <J)

«ico'0

3 ...Q).0E='z

2 c:o:lQ)

::::E

OctSepAugJulJunMayMar

EJ Insects

~ Bats

Feb

1.0

1.2

0.8

0.2

0.0

0.6

0.4

-uQ)<J)

c:

FIGURE 2. Mean insect biomass and mean numbers of the Hawaiian hoary bat seen at Ocean View on the islandof Hawai'i, in different months of 1992.

TABLE 3

ELEVATION AND VEGETATION ASSOCIATED WITH EACH BAT FORAGING SITE

LOCATION ELEVATION (m) VEGETATION TYPED

Kipiihoehoe Natural Area ReserveManukii Natural Area ReserveRed Cinder RoadHighway II (70-mile marker)Kaimii BayKalapanaKal6pii State ParkHonoka'aWaimanu BayKe6kea BayOcean ViewP6hakuloa

Wai'ono RanchHawai'i Volcanoes National Park

386548593593

Sea level60549354

Sea levelSea level

6651,830

1,0701,220

'0 'hia lowland mesic forest'0 'hia lowland mesic forest'0 'hia lowland mesic forest/eucalyptusEucalyptus trees/exotic shrubsOpen oceanOpen lava'0 'hia/eucalyptus forestEucalyptus/macadamia orchardOpen oceanOpen ocean'O'hia lowland mesic forestMamani-naio (Sophora chrysophylla-Myoporum

sandwicense) open woodland'0 'hia forest interspersed with grass fieldsKoa (Acacia koa) forest

NNME

ME

NN

NN

aN, nalive; E, exotic; M, mixed (native and exotic).

Hawaiian Hoary Bat on Island of Hawai·i-.JACOBS

range of 0-1830 m (Table 3). The climaticconditions experienced by these bats thereforerange from tropical to temperate. At eleva­tions below 1500 m, temperatures above 35°Care infrequent and the range between thecoldest and warmest months averages 6.5°C.The average temperature at Hilo (sea level) inAugust is 24.1°C and in January is 21.6°C.The average temperature at Mauna Loa Ob­servatory (3398 m) in January is 5°C and inAugust is 8°C (Blumenstock and Price 1972).However, at times the upper slopes and sum­mits of Mauna Loa and Mauna Kea arecovered in snow during winter months. Coldair formed immediately above this snow coverdescends into areas like Pohakuloa andHakalau, causing temperatures as low as- 15°C (Blumenstock and Price 1972). ThePohakuloa and Hakalau sites are at eleva­tions of about 1830 and 1890 m, respec­tively. The result is that these sites oftenexperience frost during winter.

RAINFALL. Bats were observed most fre­quently in areas with moderate rainfall. Eightof the 14 foraging sites had a mean annualrainfall ranging from 1016 mm to 1905 mm.Four had a mean annual rainfall ranging from1905 to 2540 mm. Pohakuloa had a meanannual rainfall of 508 mm (rainfall figuresfrom Armstrong [1973]).

Bats at Red Cinder Road and Kipahoehoesites generally were not active when it rained.In fact on nights when it rained just before orjust after the time the bats were usually seenat those sites, the foraging aggregations didnot appear and at most one or two bats wereseen. However, at Kalopa State Park on thewindward side of the Island, two bats wereobserved foraging in a light rain for at least30 min.

WIND. In general there was little to nowind at the inland foraging sites. The tallvegetation characteristic of most of thesesites provided a natural windbreak. However,these bats are fairly strong flyers. I haveobserved them flying without much difficultyin fairly strong winds. At Pohakuloa, where thevegetation was predominantly low mamani­naio (Sophora chrysophylla-Myoporum sand-

199

wicense) forest, wind speed ranged from 3to 6 km hr-1 , occasionally gusting to 11 kmhr-1

, on 60% of the nights surveyed.

DISCUSSION

Visual observations and echolocationmonitoring suggest that the Hawaiian hoarybat is fairly widespread around the island ofHawai'i. Although bats appear to be moreabundant on the drier leeward side of theIsland, they may not be as rare on the wind­ward side of the Island as previously thought(Kepler and Scott 1990). The largest foragingaggregation (II bats) was seen in September1990 over Keokea Bay on the windward coast.Large groups of bats have been reported onthe windward side of the island: 12 bats overHilo Bay in September 1963 and 22 bats atHonoka'a landing in October 1964 (Tomich1986). A more extensive survey of that coast­line needs to be undertaken. I have receivedreports from surfers of bats foraging overwater all along that coast.

There seems to be a decrease in bat activityfrom February to August (Table 2). The dropin activity occurs over a wide elevational andgeographical range. In addition, bats are pres­ent as early as May at Ocean View andPohakuloa (Bradshaw Military Airfield), twosites with very different elevations and geo­graphical locations. These patterns argueagainst an elevational or geographic migra­tion within the island of Hawai'i.

The drop in bat activity with the drop ininsect biomass at Ocean View suggests thatthese bats may use a number of foraging sitesover a course of a night or a few days. Theparticular sites used depend on local insectbiomass. Radio telemetry data (unpublisheddata) indicate that bats do use more than oneforaging site per night and that a bat may stayaway from a previously visited site for up to2 weeks. If this is the case, the apparent dropin activity from February to August at somesites may be associated with times when batswere foraging elsewhere because of low insectbiomass at those sites on nights when theywere surveyed.

200

The apparent increase in bat actlVlty inSeptember/October (in terms. of the numberof sites at which bats were seen) may be theresult of young of the year fledging. Capturedata (unpublished data) suggest that lactationoccurs in June and July and young are fledgedsometime in August.

In conclusion, the numbers of bats re­ported here for the different sites at differenttimes of the year suggest that the Hawaiianhoary bat is rare and that its endangeredstatus is appropriate. The fact that the habi­tats used by this bat are more often than notassociated with native vegetation suggeststhat the major threat to its existence inHawai'i may be the destruction of nativevegetation. Protection of native vegetation is,therefore, essential to the survival of Lasiuruscinereus semotus in Hawai'i. This may becomeeven more evident when the roosting ecologyof this bat is studied.

ACKNOWLEDGMENTS

I am grateful to P. Q. Tomich and Chuckand Danny Stone for their help and encour­agement, and to Sheila Conant, Lenny Freed,and Michael Hadfield for their valuable com­ments during the preparation of this paper.This survey was funded by the Forestry andWildlife Division, Department of Land andNatural Resources, Hawai'i.

PACIFIC SCIENCE, Volume 48, April 1994

LITERATURE CITED

ARMSTRONG, R. W., ED. 1973. Atlas ofHawaii. Department of Geography, Uni­versity of Hawaii. The University Press ofHawaii, Honolulu.

BALDWIN, P. H. 1950. Occurrence and behav­ior of the Hawaiian bat. J. Mammal. 31(4):455-456.

BELWOOD, J. J., and J. H. FULLARD. 1984.Echolocation and foraging behavior of theHawaiian hoary bat, Lasiurus cinereussemotus. Can. J. Zool. 62:2113-2120.

BLUMENSTOCK, D., and S. PRICE. 1972. Cli­mates of the states: Hawaii. Pages 155­204 in E. A. Kay, ed. Natural history ofthe Hawaiian Islands. University of HawaiiPress, Honolulu.

BRYAN, E. H., JR. 1955. The Hawaiian bat.Elepaio 15: 63-64.

DUVALL, F., and R. GASSMAN-DuVALL. 1991.No bats on Maui? Look again. Elepaio51: 1-2.

FUJIOKA, K. K., and S. M. GON III. 1988.Observations of the Hawaiian bat, La­siurus cinereus semotus, in the districts ofKa'u and south Kona, island of Hawaii. J.Mammal. 69: 369-371.

KEPLER, C. 8., and J. M. SCOTT. 1990. Noteson distribution and behavior of the endan­gered Hawaiian hoary bat (Lasiurus cine­reus semotus), 1964-1983. Elepaio 50(7):1-6.

TOMICH, P. Q. 1986. Mammals in Hawai'i2nded. Bishop Mus. Spec. Publ. 76: 1-375: