Lasiurus cinereus, the hoary bat

Of the over one thousand species of megachiroptera and microchiroptera found across the globe, only a small fraction live in or even pass through temperate or other non-tropical climates via migratory routes. In the state of Maryland, there are only ten species of microchiroptera that can be found with any regularity from year to year, one of which is Lasiurus cinereus, commonly known as the hoary bat. Lasiurus cinereus is a member of the phylum Chordata, the class Mammalia, the order Chiroptera, and the family Vespertilionidae. The genus is Lasiurus, and the species name is Lasiurus cinereus, with three subspecies: L.c. cinereus, L.c. villosissimus, and L.c. semotus.

Often regarded as one of the most handsome bats in the world, the hoary bat has long, dense, white-tipped fur, striking a close resemblance to the silver haired bat, another microchiroptera common to Maryland (Tuttle 1995). Weight varies anywhere between eighteen to thirty-eight grams depending on gender and time of year, while the average total length of a full grown hoary bat is 134.8 millimeters (Bunch 121). As evidenced by these numbers, the hoary bat is one of the largest microchiroptera found in North America, although it pales in comparison to some species of bats native to Australia and other tropical locations around the world that can reach weights of up to one and a half kilograms.

One characteristic that sets Lasiurus cinereus apart from other North American microchiroptera is its widespread distribution. Hoary bats have been found in parts of northern Canada all the way south to Argentina and Chile and, uniquely, west to Hawaii (Cryan 2002). The hoary bat is one of the few tree-dwelling bats of North America, preferring the cover provided by the peeling bark, foliage, or hollow cavities of large trees located in dense forests to that of caves (Brigham 1998). This fact alone makes the task of studying Lasiurus cinereusπ range and migratory routes a daunting one due to a tree-dwellersπ solitary lifestyle and choice of remote living locations. However, it is known that hoary bats spend their summers in parts of Canada, the Midwest, the northeastern United States, and Mexico, interestingly absent from California and the Pacific Northwest, where many spend their winter. Studies show that during the spring, migratory routes cut through Arizona, New Mexico, and California, as opposed to a general migration southward and towards the coasts in the fall, predominantly the Pacific (Tuttle 1991). There has been little evidence to this date concerning the mixing of North American and South American populations of hoary bats, but this may be partly due to limited research on this topic (Cryan 2002).

The aforementioned presence of Lasiurus cinereus on the Hawaiian archipelago, commonly called the åopeπapeπa by Hawaiians, is very significant considering that it is the only land mammal to inhabit the islands (Fullard 1989). Very little is known about these bats with regard to their numbers and range among the islands, once again due to this batπs solitary nature. However, studies have pointed towards a preference for wet areas in close proximity to forests instead of drier areas and farmlands. The presence of these hoary bats over river mouths near forests on the northern coast of Kauaπi, and their subsequent absence over river mouths which are not close to forests suggests that they may use rivers as pathways to their roost sites deep within the forest (Fullard 1989). Concern over the future well-being of this bat inspired the Honolulu Chapter of the Sierra Club to form a group called ≥Save the åOpeπapeπa Project,≤ dedicated to the conservation and pursuit of knowledge about this very special microchiroptera (≥The Projectä≤ 1989).

Unfortunately, biologists have been unable to gather much information about the hoary batπs mating habits, although some discoveries have been made within the last decade. Although actual mating between hoary bats has never been witnessed by humans, scientists have concluded that they most likely mate during flight like their close relative, the red bat. After mating has occurred in early autumn or on the batsπ wintering-over grounds, the female bat will then apparently store the maleπs sperm inside of her over the winter and finally fertilize her eggs when she is ready to ovulate in the spring (Tuttle 1995). Unlike most bat species that only bear one pup at a time, Lasiurus cinereus oftentimes will give birth to twins, and sometimes have litters of up to four pups, anytime from mid-May through late June (Bouchard 2000). Mothers rearing their pups have most commonly been found in the Midwest, southern Canada, and sometimes the eastern US, while male bats are suspiciously scarce when mothers and their pups are present. The apparent lack of males in these areas may be attributed to the femalesπ preference for low elevations as opposed to malesπ liking for mountainous areas (Tuttle 1995).

The hoary bat has what may be considered a disadvantage when compared to other microchiroptera because of its large size. What Lasiurus cinereus lacks in maneuverability, it more than makes up for in flight speed thanks to its oversized wings (Barclay 1999). Consequentially, the hoary bat echolocates at a lower frequency than most other microchiroptera, and will even emit social calls at about 9.8 kHz, much lower than the standard 15 to 30 kHz range and well within the range of human hearing. The reason they echolocate at a significantly lower frequency is because the lower frequency calls will travel a longer distance, which is well suited to a bat whose speed overrides its agility when hunting its prey (Tuttle 1995). Interestingly, the echolocation of the Hawaiian hoary bat is slightly different than that of the mainland bat in that the åopeπapeπa echolocates at the higher frequency common to most bats. This difference can be attributed to the Hawaiian batπs smaller size and the variation between insects regarded as prey on the mainland and in Hawaii (Barclay 1999). While hunting, Lasiurus cinereus shows a preference towards moths over all other types of insects. This preference may be due to the fact that it is easier for a hoary bat to capture a larger moth as opposed to smaller prey, such as a mosquito, because of the lower frequency of his calls during echolocation (Altringham 105).

Although many recent findings have started to clarify the world of the hoary bat, tons of information about this solitary tree-dweller has yet to be discovered. The hoary batπs mating rituals, migratory patterns, intermixing between populations on different continents, and roosting habits are all puzzles in which only some of the pieces have been found, while the majority are still waiting to be put into place. This beautiful bat will surely entertain the focus of many biologists and bat fanatics for years to come.

Works Cited

Altringham, John D. Bats: Biology and Behaviour. New York: Oxford University Press, 1996.

Barclay, Robert M. et al. ≥Variation in the Echolocation Calls of the Hoary Bat.≤ Canadian Journal of Zoology 77 (1999): 530-534.

Bouchard, Sylvie et al. ≥Autumn Mating and Likely Resorption of an Embryo by a Hoary Bat, Lasiurus cinereus.≤ The American Midland Naturalist 145.1 (2000): 210-212.

Brigham, R. Mark et al. ≥Hide and Seek: In Search of Forest Bats.≤ Bats Magazine 16.1 (1998): 3-7.

Bunch, Mary S. et al. ≥The Distribution of the Bats of South Carolina.≤ Southeastern Naturalist 2.1: 121-152

Cryan, Paul M. ≥Seasonal Distribution of Migratory Tree Bats in North America.≤ Journal of Mammalogy 84.2: 579-593.

Fullard, James H. ≥πOpeπapeπa: Hawaiiπs Elusive Native Bat.≤ Bats Magazine 7.3 (1989): 10-13.

≥The Project to Save the Hawaiian Bat.≤ Bats Magazine 7.3 (1989): 11.

Tuttle, Merlin D. ≥How North Americaπs Bats Survive the Winter.≤ Bats Magazine 9.3 (1991): 7-12.

Tuttle, Merlin D. ≥The Little Known World of Hoary Bats.≤ Bats Magazine 13.4 (1995): 3-6.