The Hoary Bat is the largest bat in British Columbia. It has a distinctive hoary colour. The long, soft fur on its back is a mix of dark brown and grey hairs that are tinged with white. There are small patches of yellow or white on its shoulders and wrists. Yellow fur also appears on the throat, around the ears and on the underside of the wing membranes. The wing membranes are dark brown with paler areas on the forearm and fingers. The ears are round and short with a short, broad tragus. The outer edge of the ear is black; yellow hairs are scattered on the inside of the ear. The dorsal surface of the tail membrane is densely furred; the hind foot is relatively small with a heavy covering of fur on the upper surface. The calcar has a narrow keel. The skull has a short, broad rostrum, large molars and a high profile.
The large size and marked colour pattern make the Hoary Bat one of our most distinct bats. The only species with remotely similar markings is the Silver-haired Bat (Lasionycteris noctivagans)-see that account for diagnostic external features. Among British Columbian bats, only the Western Red Bat (Lasiurus blossevillii) has a similar dental formula; the skull of the Hoary Bat can be discriminated by its greater size (skull length greater than 15 mm).
incisors: 1/3 canines: 1/1 premolars: 2/2 molars: 3/3 The tiny first upper premolar is usually hidden between the canine and second upper premolar.
total length: 137 (125-144) n = 11 tail vertebrae: 60 (50-66) n = 10 hind foot: 12 (10-15) n = 12 ear: 14 (13-16) n = 4 tragus: 9 (9-10) n = 4 forearm: 54.5 (50.3-57.4) n = 24 wingspan: 392 (338-415) n = 7 weight: 28.4 (20.1-37.9) n = 43
Mating likely takes place during the autumn migration or in winter; females are pregnant during the spring migration. Although there are no breeding data available for British Columbia, in other parts of Canada young are born in June and nurse from early June to the end of July. Normally females leave the young at the roost at night, but they can carry their young for about a week after birth. Females typically give birth to twins, although one, three or four young have also been observed. The newborn bats are undeveloped with closed eyes and ears. The top of the head, shoulders and tail membrane are covered with fine, silver-grey hairs and the underside is naked. Development is slow with the ears opening within three days and the eyes in around twelve days. By five weeks the young are capable of sustained flight. Even after the young are flying, family groups remain together for several more weeks. The relatively lengthy period of parental care shown by female Hoary Bats may be because this mammal does not hibernate - it has fewer energy demands than hibernating bats, which have to accumulate fat reserves for winter.
Hoary Bats emerge about 30 minutes after sunset to feed and continue to forage throughout the night. Nursing females reduce their foraging time during the the first few weeks of nursing to spend more time with their young at the roost.
The Hoary Bat is suited to preying on large insects, with its large skull and teeth and its swift flight. It emits low-frequency echolocation calls that are most effective for detecting large prey at long range. The Hoary Bat hunts at tree-top level in open areas such as fields and forest clearings. Large moths, beetles and dragonflies form the bulk of its diet; small insects, such as midges and flies, are less common prey.
The Hoary Bat is often attracted to insect concentrations at lights outside buildings; permanent outdoor lights may even be responsible for its presence at some locations in the province. In well-lit areas where insect prey are concentrated, a Hoary Bat will establish a feeding area and chase away other bats (including other Hoaries). Loud chirping calls audible to the human ear are often emitted during these chases. Besides their role in communication, these calls may also provide some echolocation information.
Because of its tendency to roost in the branches of coniferous and deciduous trees, the Hoary Bat is often referred to as a tree bat. Specific details on tree roosts in British Columbia are not available - only a few individuals have been found roosting in the branches of fruit trees in the Okanagan. In Manitoba the Hoary Bat roosts some 8 to 12 metres above the ground, usually near the ends of branches of deciduous trees such as Green Ash. It seems to select sites that will conceal it from predators and yet also provide an open flight path for easy access to and from the roost. In Oregon the Hoary Bat prefers old Douglas-fir forests, presumably because of its tree-roosting habits. Although its usual day roosts are in the branches of trees, the Hoary Bat has been found roosting in tree cavities in British Columbia: one was collected from a hollow cedar tree in Garibaldi Provincial Park and another was found in a woodpecker nest in a tree cavity. The Hoary Bat rarely roosts in caves or buildings.
In summer, males are solitary and females roost with their young. Unlike most of our bats, females do not congregate in maternity colonies. Because their tree roosts are more exposed than the maternity roosts of other bats, females will stay with their undeveloped young for longer periods to keep them warm. Family groups will use the same roost for more than a month.
Circumstantial evidence based on seasonal occurrences in British Columbia strongly suggests that the Hoary Bat is migratory. There are records from 19 June to 15 October with most from mid August to early October, the period when the autumn migration is presumed to take place. The winter range of British Columbian populations is unknown. It appears that populations in the Pacific Northwest migrate to southern California or Mexico for the winter.
The Hoary Bat is associated with a variety of forested and grassland habitats in the province. Its elevational range is from sea level to 1250 metres.
The Hoary Bat has the broadest distribution of any North American bat ranging from South America to northern Canada. It has managed to colonize a number of isolated islands including the Hawaiian Islands. In British Columbia, it is found on Vancouver Island, the coastal mainland north to Garibaldi Provincial Park, and the southern interior north to the Williams Lake region. In some regions of North America the sexes appear to occupy separate summer ranges. Based on the few available records the sexes appear to overlap extensively in British Columbia.
One subspecies, L.c. cinereus, is recognized in North America.
The thick, heavy fur covering on the body and tail membrane of this bat is important for insulation. The hoary colour provides camouflage against a background of lichen-covered bark. Because of its solitary roosting habits in trees, the Hoary Bat is rarely encountered by man. There is still much to be learned about its distribution and roosting behaviour in the province. It is a bat that can be easily identified and we encourage naturalists to report any observations.
Recommended citation: Author, Date. Page title. In Klinkenberg, Brian. (Editor) 2019. E-Fauna BC:
Electronic Atlas of the Fauna of British Columbia [efauna.bc.ca]. Lab
for Advanced Spatial Analysis, Department of Geography, University of British
Columbia, Vancouver. [Accessed:
22/11/2019 12:46:46 PM]
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