Known locally as the 'ope'ape'a, the Hawaiian Hoary bat is the only existing
native terrestrial mammal known to occur in the Hawaiian archipelago, although other bat species have been found
in subfossil remains. The Hoary Bat is today found on Hawai'i Maui, O'ahu, Kaua'i and Moloka'i with unconfirmed
observations from Kaho'olawe. The largest concentrations of bats are considered to occur on Hawai'i and Kaua'i.
On the Big Island most observations have been from between sea level and 7,500 feet elevation, although individuals
have been recorded at elevations as high as 13,200 feet.It is suspected that the number of bats has decreased in the past 100 years or so due to habitat loss, although population numbers are not known. Other threats which affect the bats are the availability of roosting sites, pesticides (directly and indirectly), predation, changes in the composition and availability of food, and roost disturbance.
The Hawaiian Hoary Bat was listed as endangered by the U.S. Fish and Wildlife Service on 13th October 1970 and assigned a recovery plan which indicates a subspecies with moderate degree of threat and a high potential for recovery.
The Hawaiian Hoary Bat is a medium-sized nocturnal, insectivorous species, which averages 14-22 grams in weight. The species is heavily furred and they possess a brown-grey hair colouration, which is tinged with white, producing a "hoary" appearance. The bat has short, thick, rounded ears which are edged black. The Hawaiian species may be somewhat more red in colour than the North American Hoary Bat. The Hawaiian species is about 45 % smaller in mass than the American counterpart and females are larger than males (females average 17.9 grams, males average 14.2 grams). Both sexes have a wingspan of about 26.9 - 34.6 centimetres.
The Hawaiian Hoary Bat belongs to the suborder Michrochiroptera, which includes all bats except Old World fruit bats. The taxonomic treatment of the genus Lasiurus varies from authority to authority. Koopman (1993) recognised seven species, including five in North America alone; Jones et al (1992) recognised seven species in North America north of Mexico; and Nowak (1994) recognised thirteen species. The Hawaiian Hoary Bat is one of three recognised Hoary Bat subspecies; Lasiurus cinereus cinereus occurs throughout North America, and L.c. vilosissimus occurs in South America.
The Hawaiian species is endemic to the Hawaiian Islands and is thought to have derived from the North American Hoary Bat. Jacobs (1993) has presented morphological evidence suggesting that significant divergence of the Hawaiian species from the mainland form has occurred, and Tomich (1986) has suggested classification as a full species may be appropriate. However, Morales and Bickham (1995) found that a relatively low genetic divergence had occurred between the Hawaiian and mainland forms, and thus argue that sub-specific status for the Hawaiian form is more appropriate.
Only a small amount of research has been conducted on the Hawaiian Hoary Bat, but diet and echolocation practices have been studied, as well as numerous surveys. The species is a solitary bat that roosts among the foliage of trees. During a 2-week period Jacobs (1993) found that two radio-tagged bats returned to the same roosting area each night, and possibly used the same roosting tree. However it has been suggested that roost site fidelity may vary seasonally and with reproductive condition; fidelity to a home area may be more prevalent than fidelity to a specific roost among foliage roosting bats. Jacobs (1993) also found that bats typically departed the roost shortly before sunset and returned before midnight, although this is based on a small number of observations.
The Hawaiian Hoary Bat has been observed foraging in a variety of habitats, both open areas and more vegetatively cluttered habitats, including open fields near native and non-native woodland, over open ocean (in bays near shore), over lava flows and at streams and ponds. The North American Hoary Bat forages almost exclusively in open areas away from vegetation. The Hawaiian form has been observed feeding from 1 metre to over 150 metres above the ground or water.
The North American Hoary Bat feeds primarily on moths (Black, 1972) and Bellwood and Fullard (1984) found similar food stuffs were important for the Hawaiian form on Kaua'i. Having said this, other researchers have found no particular food selection more common in bats studied in both Canada and Hawai'i. Jacobs (1993) has suggested that the Hawaiian form has a more varied diet compared to mainland bats, possibly due to morphological differences between the two subspecies, including the fact that the Hawaiian form has a smaller body size and relatively larger skull size.
Pregnant bats have been documented on both Hawai'i and Kaua'i. It may be that males in Hawai'i are fertile all year-round, although breeding probably occurs mostly between September and December, with birth of the young occurring in May or June. One female was reported to have been possibly pregnant in April, and large fetuses were found in females collected in May and June (Baldwin, 1950). Lactating females have been recorded between late June and early August, and females examined between September and December were post-lactating (Tomich, 1986).
Most temperate insectivorous bats exhibit sperm storage and delayed fertilisation in which adults breed in the fall and sperm is stored in the females reproductive tract until spring, when ovulation and fertilisation occurs. This has not been confirmed in Hawaiian Hoary Bats, but is presumed to occur in the mainland form.
Hawaiian Hoary Bats are non-migratory, although seasonal elevation movements and island-wide migrations may occur. The North American form is migratory with Canadian and northern States individuals travelling south to central and southern States, and even further south. The activity of Hawaiian bats apparently varies seasonally, although the exact nature of these movements is unclear. Kepler and Scott (1990) found that most observations of bats was between August and December. On the Big Island 82 percent of the observations occurred during this period, although the greatest sampling effort was between May and August. Other researchers found fewer bats in November and December. On Kaua'i Telfer (1992) found that there was a decrease in observations between May and September in some areas.
Kepler and Scott (1990) suggested that reduced activity may be due to bats entering torpor (a dormant state with reduced metabolic rates) during the winter months as well as the possible appearance of newly fledged young.
It has not yet been established whether native vegetation is required or is important to the Hawaiian form, although loss of native vegetation may account for the reported decrease in numbers in the Islands. Kepler and Scott (!990) found that they were more frequently observed in association with non-native vegetation, with only a few occurring in native vegetation. However, with the marked increase in non-native species in the last century or so, the numbers of bats recorded would undoubtedly increase. Fullard (1989) found on Kaua'i that bats frequented areas near native forest though, rather than near towns or open fields. Fullard (1989) also found bats commonly foraging over ocean outlets of forested rivers on Kaua'i.
Roosting bats have been recorded from a variety of species including hala (Pandanus tectorius), Kukui (Aleurites moluccana), Pukiawe (Styphelia tameiameiae) and Java Plum (Syzygium cumini). They have also been frequently recorded roosting in Eucalyptus trees.
Current and Historic Range and Population Status
The Hawaiian Hoary Bat is known from the islands of Hawai'i, Maui, O'ahu, Kaua'i and Moloka'i, although may only be resident on Hawai'i, Maui and Kaua'i. There are no records for Lana'i and just one unconfirmed sighting for Kaho'olawe. The population may have been quite large on O'ahu prior to the early 19th century, but this is based on a single observation of an unknown number of bats at an unknown location (Tomich 1986). The largest populations are currently considered to exist on Kaua'i and Hawai'i.
Actual numbers or even estimated population size are not known. Estimates have put the population at thousands, but this is based solely on individual observations, rather than any sort of quantified survey methods. Observations were apparently widespread on Hawai'i and Kaua'i between 1939 and 1986 (Tomich 1986). Bats occur in both dry and wet areas, but appear to be more common on the drier leeward side (Jacobs 1994). Fullard (1989) reported that on Kaua'i the bat was "not common" and is apparently limited to the northern forested zones of the island, but more recent anecdotal evidence suggests that bats are common there (A.Asquith, U.S. Fish and Wildlife Service, pers.comm. 1997). It is certainly true that bats are quite commonly seen along the northern edge of the island, from sea level to high elevation forest and individuals have been recorded quite frequently on the south-east (Lihue area) and south (Koloa) areas (C.W. Melgar, unpublished field notes. 1998, 1999, 2000, 2001). Kepler and Scott (1990) suggested that bats found on O'ahu, Maui and Moloka'i may be migrants or vagrant individuals , although more recent data suggests that bats are resident on Maui. Two bats have been documented on Moloka'i, where one was seen over open ocean. At present the seasonal bias, distribution and numbers of bats recorded may be an effect of research effort and location of observation and so any information must be treated with a certain amount of caution.
Reasons for decline and current threats and conservation
As there is very little overall data and as historical information regarding its past distribution is scant, the decline of the bat has largely been inferred. Observations and specimen records appear to show that bats are now absent from historically occupied ranges, although numbers of individuals in these areas is lacking. The population of the Hawaiian Hoary Bat could be threatened by habitat loss, pesticides, predation and roost disturbance. Fenton and Barclay (1980) and others, suggest that in general, the availability of roosting sites rather than food availability, predation or other factors is believed to be the primary limitation in distribution and abundance of many bat species (Fenton 1970, Humphrey 1975).
It would seem however that in the Hawaiian islands there is still a large enough amount of forest (native and non-native) to support a large population of bats. Predation in Hawai'i is probably limited to the indigenous Hawaiian Short-eared Owl (Asio flammeus sandwichensis) and introduced Barn Owl (Tyto alba), although several other species of Owl were present in the Islands before the first Polynesians arrived and so it is unlikely that predation by Owls has increased very much. On Hawai'i the endemic Hawaiian Hawk or I'o (Buteo solitarius) is present, but is a diurnal hunter and the two species probably do not meet very often.
Pesticide use has increased markedly in the last century, especially with the rise in the amount of area taken up by sugar cane and this may have a marked effect on the amount of available food for bats. Now that the sugar cane industry in Hawai'i is on the way out, perhaps we will see a rise in the number of bats.
Disturbance of roost sites could easily occur in human-inhabited areas, but in the more remote forested areas (even near towns etc), disturbance is likely only from introduced rats and cats, and possibly foraging ungulates, such as pigs and goats.
The Hawaiian Hoary Bat was listed as endangered on 13th October 1970, which means that it is considered likely that the species is in danger of extinction throughout all or part of its range. The Bat is fully protected by law and this prohibits the taking, harassing, pursuance, wounding, killing, trapping, capturing or collection of any individuals.
Where to see Hawaiian Hoary Bats in Hawai'i
Clearly by reading the above account it is not a species which can be predicted with any ease where a sighting may be best achieved. The following maps show locations of observations in recent times, as shown in the Hawaiian Hoary Bat Recovery Plan.
