Lasiurus cinereus - Hoary Bat

Description:

This bat is larger than all other bats in the genus Lasiurus (Eisenberg and Redford 1999). The total length ranges from 134 to 140 millimeters (mm), head and body measure around 85 mm, and forearm ranges from 46 to 55 mm. The wing spread is 380-410 mm (Barbour and Davis 1969). The ears are short, rounded, and edged with black. The dental formula is I 1/3, C 1/1, P 2/2, M 3/3 (Eisenberg and Redford 1999). The fur color on the back ranges from yellowish brown to mahogany brown, but the tips of the hairs are white. The underside is white to a yellowish color. The young have a forearm length of 18-19 mm (Barbour and Davis 1969). There skin is brown with the body being darker than the wings and lighter on the dorsal side. The hoary bat does not have a nose leaf; the tragus on the bat is narrow and on a stalk in front of ear, and the tail is long and entirely within the membrane (Emmons and Feer 1997).

Distribution:

This species is well known for migrating and has a very large distribution (Eisenberg and Redford 1999). It actually has the largest distribution of any American bat (Bouchard et al 2001). It ranges from southern Canada to southern Argentina (Eisenberg and Redford 1999). It can survive in different elevations, even up to 1,456 meters (m).

One study found it only in 2 eastern biomes (Alto Paraná and Ñeembucú) in Paraguay (Willig et al 2000). Alto Paraná is forested with very high precipitation and humid conditions. However, Ñeembucú is a grassland area with high precipitation and semi humid conditions. The 2 areas are similar in that the topography is hilly.

Ontogeny and Reproduction:

Its breeding range is found in Canada and north central and northeastern U.S. (Barbour and Davis 1969). Mating usually occurs during autumn migration (Bouchard 2001). The bat usually arrives in Canada in late May and gives birth to twins in early June. Females spend time after giving birth alone in a roost in foliage of trees (Ransome 1990). Females usually give birth to 1 or 2 young. They leave their young while foraging. The time spent foraging depends on the maturity of the young. Shorter time periods are 150 minutes and increase to 375 when the young can fly. Females with 2 young forage for longer times and depart earlier than females with 1 young.

High energetic demands during pregnancy and parturition are not usually fulfilled in temperate climates (Ransome 1990). This is mainly due to the availability of insects. Therefore pregnancy is usually extended. Lactation periods occur when insect availability is the greatest and most reliable. Females consume more and use more energy during lactation. Females are more efficient predators after birth because of a lower wing loading.

Females can be expected to have as many as four young since it has 4 mammae but generally has 2 (Allen 1939). Parturition occurs from the middle of May into early July (Barbour and Davis 1969). The newborn are blind and cling to the mother when she is not foraging. The female will move her young if the roost is disturbed. The growth rate of this bat is affected by temperature and rainfall (Koehler and Barclay 2000). It has been shown that the young can grow faster in warmer temperatures but grows slower with the increase in precipitation.

Ecology and Behavior:

This bat generally selects moist areas to live in but has been known to use dry deciduous forests and even evergreen forests (Eisenberg and Redford 1999). The color of their fur serves as camouflage against vegetation (Emmons and Feer 1997). One study found that the bats used old growth white pine mixed wood stands than other stands in Ontario (Jung et al 1999). They also use more open canopy woods since they have high aspect wings. They like roosts that are covered above but open below (Barbour and Davis 1969). It hangs up singly among the foliage of trees by itself (Allen 1939). The roosts are 10-15 ft above the ground and along the edges of clearings (Barbour and Davis 1969). This bat also goes into torpor frequently to conserve energy (Koehler and Barclay 2000, Barclay et al 1999).

Another unique aspect of this bat is it has a very low frequency call than most other bats, which probably relates back to it having high wing loading and less maneuverability (Barclay et al 1999). The call ranges from 20 to 17 kHz. It is one of only a few bats that make an audible chattering sound (Barbour and Davis 1969). Their flight movements are swift and direct compared to smaller bats (Barbour and Davis 1969, Ransome 1990).

The hoary bat is insectivorous and usually solitary (Koehler and Barclay 2000). Moths, dragonflies, and beetles make up most of its diet (Ransome 1990).  They are more active over covered areas than over water and are concentrated along the edges of woods. They are known to feed by street lights in rural areas or towns benefited by the increased abundance of insects. They emerge late in the evenings but have been seen to come out before dark (Barbour and Davis 1969). It is also migratory and leaves early at night to migrate. During migration they move in waves with many individuals. The behavior of this bat is not well known in the tropics (Emmons and Feer 1997).

Remarks:

Literature Cited:

Allen, G. M. 1939. Bats. Dover Publications, Incorporated, New York, New York, USA.

Barclay, M. R., Fullard, J. H., Jacobs, D. S. 1999. Variation in the echolocation calls of the hoary bat (Lasiurus cinereus): influence of body size, habitat structure, and geographic location. Canadian Journal of Zoology 77:530-534.

Barbour, R. W. and W. H. Davis. 1969. Bats of America. The University Press of Kentucky, Lexington, Kentucky, USA.

Bouchard, S., Zigouris, J., Fenton, B. M. 2001. Autumn mating and likely resorption of an embryo by a hoary bat, Lasiurus cinereus (Chiroptera: Vespertilionidae). American Midland Naturalist 145:210-212.

Eisenberg, J. F. and K. H. Redford. 1999. Order Chiroptera. Page 202 in. Mammals of the neotropics, volume 1, The central neotropics: Ecuador, Peru, Bolivia, Brazil. University of Chicago Press, Chicago, Illinois, USA.

Emmons, L. H., and Feer, F. 1997. Neotropical rainforest mammals: a field guide. Second edition. The University of Chicago Press, Illinois, USA.

Jung, T. S., Thompson, I.D., Titman, R.D., Applejohn, A.P. 1999. Habitat selection by forest bats in relation to mixed-wood stand types and structure in central Ontario. Journal of Wildlife Management 63:1306-1319.

Koehler, C. E. and M. R. Barclay. 2000. Post-natal growth and breeding biology of the hoary bat (Lasiurus cinereus). Journal of Mammology 81:234-244.

Ransome, R. 1990. The natural history of hibernating bats. Christopher Helm (Publishers) Limited, Imperial House, Kent, South Dakota, USA.

Willig, M. R., Presley, S. J., Owen, R. D., González, C. L. 2000. Composition and structure of bat assemblages of in Paraguay: A subtropical -temperate interface. Journal of Mammalogy 81:386-401.

Reference written by Calvin Kunkle, Biology 378 (Mammalogy), University of Wisconsin – Stevens Point.  Edited by Christopher Yahnke. Page last updated August 8, 2005.