Eastern red bat (Lasiurus borealis)
|Also known as:||red bat|
|Size||Head-body length: 5 - 9 cm (2)|
Tail length: 4.5 - 6.2 cm (3)
Wingspan: 29 - 33.2 cm (3)
Forearm length: 3.7 - 4.2 cm (3)
|Weight||7 - 16 g (3) (4)|
Classified as Least Concern (LC) on the IUCN Red List (1).
Described as one of the most beautiful of all North American bats (3), the eastern red bat is a distinctive species characterised, as its name suggests, by its bright red to rusty-red fur. The fur is soft and dense, and the individual hairs may be tipped with white, giving a ‘frosted’ appearance (2) (3) (4) (5). The underparts are slightly paler (4), while the front parts of the shoulders have a buffy white patch (3) (4) (5). The ears of the eastern red bat are short, broad and rounded, with a triangular tragus, and are densely furred on most of the outer surface (3) (4). The long tail is another distinctive feature of this species, as is the heavily furred upper surface of the interfemoral membrane (2) (3) (4), from which the genus name, Lasiurus (meaning ‘hairy tail’), is derived (4). The wings are long and narrow, and fur extends along the underarms to the wrist (3) (4) (5).
Unusually, male and female eastern red bats are quite contrastingly coloured, the female usually having a duller, more greyish coat while the smaller male is a brighter red (2) (3) (4) (5). However, this colour difference may be linked to body size, with smaller individuals of both sexes tending to be redder (6). Despite its bright fur, the eastern red bat is surprisingly well camouflaged when hanging in a tree, wrapped in its furry tail membrane, often resembling a dead leaf or pine cone (1) (5) (7). Although a number of subspecies of red bat were once recognised (4), these are now generally considered separate species (8). The eastern red bat can be particularly difficult to distinguish from its closely related western counterpart, the western red bat (Lasiurus blossevillii) (5), with which it was once considered conspecific (4).
The eastern red bat occurs across eastern North America, east of the Rocky Mountains, from southern Canada to north-eastern Mexico (1) (2) (3) (5) (7). It has also been recorded on Bermuda (1) (2) (3) (8).
Often known as a ‘tree bat’, the eastern red bat usually roosts amongst foliage in trees or shrubs (1) (2) (4) (5) (7), choosing a site which is free of branches below, to leave a clear flight path (3) (4) (9). Roost sites may be used by different individuals on different days (4). Feeding usually takes place in wooded areas, along water courses or the edges of pasture or other open habitat, or even in urban areas, often around street lights (2) (3) (4) (5) (7), although heavily urbanised areas are avoided (1). In winter, hibernating eastern red bats have been found in hollow trees, old squirrel nests and even on the ground, amongst leaf litter (3) (5).
The eastern red bat begins feeding in the early evening (2) (5) (7), and eats a variety of insects (1) (3) (4) (5). Prey is typically caught in flight (1) (2), although this species will also land to pick insects off vegetation or even from the ground (2) (5). The eastern red bat is highly migratory, moving south from September to November to hibernate, and travelling north again between March and April (1) (2) (3). During hibernation, it is able to survive quite drastic temperature fluctuations, thanks to its thick fur, short ears (which minimise heat loss), and the heavily furred tail membrane, which adds to the bat’s insulation when wrapped around the body (3) (4) (7). The body temperature must be maintained above freezing (1) (3) (7), but the eastern red bat arouses from hibernation at higher temperatures than bats that hibernate in caves, which prevents it from waking too frequently and wasting precious energy reserves (3). Male and female eastern red bats appear to migrate at different times and to have different summer ranges (4) (5).
Although generally solitary, the eastern red bat may migrate in flocks of up to several hundred individuals. Mating takes place in flight, between August and September, although the female stores the sperm until the following spring, with fertilisation usually occurring around March or April. The young are born from late May to early July, after a gestation period of 80 to 90 days (2) (3) (4). Unusually for a bat, the female eastern red bat may give birth to a large litter of up to five young (although two or three are more common) and has four mammary glands rather than the usual two (1) (2) (3) (4) (7). The young bats are born blind and hairless and are suckled for around 38 days. The eyes open after three to four weeks, and the young first fly at four to five weeks old (1) (3) (4).
The eastern red bat is not currently considered at risk of extinction (1), and indeed is believed to be one of the most common bats in many parts of its range (3) (5) (7). In general, as a solitary species that does not usually roost in buildings, it rarely comes into direct conflict with humans (3), However, reports of much larger migratory flocks in the late 1800s suggest that the eastern red bat may have declined substantially in the last century (5) (7), and some studies also indicate more recent declines (10). Given that some individuals have been found to hibernate in grass and leaf litter, controlled burning in autumn and winter may pose a potential threat (5) (7), and the eastern red bat is also one of the bat species most frequently found killed at wind turbine facilities in North America, raising concerns about the potential impacts of these developments on bat populations. The exact causes of these deaths, however, remain unclear (11) (12).
The eastern red bat is found in a number of protected areas (1). However, very little is currently known about the status, winter habitat or behaviour of this distinctive species (5) (7), partly as it does not form large colonies that are easy to survey (5). It may therefore benefit from further research, particularly into the causes of fatalities around wind turbines (11) (12). Certain habitat management measures may also be beneficial to this species, such as maintaining hedgerow habitats along crop borders, planning burning activities to minimise bat mortality (5), and retaining large trees in urban areas, as these provide important roosts in an otherwise cleared and fragmented habitat (9).
For more information on bat conservation see:
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- Conspecific: belonging to the same species.
- Fertilisation: the fusion of gametes (male and female reproductive cells) to produce an embryo, which grows into a new individual.
- Genus: a category used in taxonomy, which is below ‘family’ and above ‘species’. A genus tends to contain species that have characteristics in common. The genus forms the first part of a ‘binomial’ Latin species name; the second part is the specific name.
- Gestation: the state of being pregnant; the period from conception to birth.
- Hibernate: hibernation is a winter survival strategy in which an animal’s metabolic rate slows down and a state of deep sleep is attained. Whilst hibernating, animals survive on stored reserves of fat that they have accumulated in summer.
- Interfemoral membrane: the skin that stretches between the hind legs and tail of a bat, used in flight.
- Mammary glands: the organs of females that produce milk.
- Subspecies: a population usually restricted to a geographical area that differs from other populations of the same species, but not to the extent of being classified as a separate species.
- Tragus: a soft cartilaginous projection extending in front of the external opening of the ear. In bats, it plays an important role in filtering returning echoes in echolocation.
IUCN Red List (July, 2010)
- Nowak, R.M. (1991) Walker’s Mammals of the World. The Johns Hopkins University Press, Baltimore and London.
- Whitaker Jr, J.O. and Hamilton Jr, W.J. (1998) Mammals of the Eastern United States. Cornell University Press, Ithaca.
Shump, K.A. and Shump, A.U. (1982) Lasiurus borealis. Mammalian Species, 183: 1-6. Available at:
Texas Parks and Wildlife Department: Eastern Red Bat (Lasiurus borealis) (August, 2010)
- Davis, A.K. and Castleberry, S.B. (2010) Pelage color of red bats Lasiurus borealis varies with body size: An image analysis of museum specimens. Current Zoology, 56(4): 401-405.
Bat Conservation International (August, 2010)
Wilson, D.E. and Reeder, D.M. (2005) Mammal Species of the World. A Taxonomic and Geographic Reference. Third Edition. The Johns Hopkins University Press, Baltimore. Available at:
- Mager, K.J. and Nelson, T.A. (2001) Roost-site selection by eastern red bats (Lasiurus borealis). American Midland Naturalist, 145(1): 120-126.
- Winhold, L., Allen, K. and Rodney, F. (2008) Long-term change in an assemblage of North American bats: are eastern red bats declining? Acta Chiropterologica, 10(2): 359-366.
- Cryan, P.M. and Barclay, R.M.R. (2009) Causes of bat fatalities at wind turbines: hypotheses and predictions. Journal of Mammalogy, 90(6): 1330-1340.
- Kunz, T.H., Arnett, E.B., Erickson, W.P., Hoar, A.R., Johnson, G.D., Larkin, R.P., Strickland, M.D., Thresher, R.W. and Tuttle, M.D. (2007) Ecological impacts of wind energy development on bats: questions, research needs, and hypotheses. Frontiers in Ecology and the Environment, 5(6): 315-324.