MAMMALS OF MISSISSIPPI 5:1–8 Big brown bat (Eptesicus fuscus) ALISHA A. WORKMAN Department of Wildlife and Fisheries, Mississippi State University, Mississippi State, Mississippi, 39762, USA Abstract—Eptesicus fuscus (Beauvois, 1796) is a vespertilionine commonly called the big brown bat. It is sexually dimorphic with the female being slightly larger than the male. Dorsal color ranges from pinkish tan to rich chocolate and the ventral color ranges from pink to olive buff. It represents one out of twenty four in the genus Eptesicus. Eptesicus fuscus is distributed through all of the United States except Hawaii, most of Central America except the Yucatan Peninsula, and its southern limit is northwestern South America. Eptesicus fuscus generally prefers to live in caves, trees, bridges, and buildings. Eptesicus fuscus is currently not listed as a species of special concern. Published 5 December 2008 by the Department of Wildlife and Fisheries, Mississippi State University Big Brown Bat GENERAL CHARACTERS Eptesicus fuscus (Beauvois, 1796) The big brown bat, Eptesicus fuscus (Fig. 1), is one of the most common bats in North America CONTEXT AND CONTENT. (Barbour and Davis 1969). The pelage color Order Chiroptera, Suborder Microchiroptera, varies by geographic location, but ranges from Family Vespertilionidae, Subfamily pinkish tan to rich chocolate on the dorsal Vespertilioninae, Tribe Vespertilionini. side and pink to olive buff on the ventral side. The bare-skin areas of the face, wings, and ears are black. The fur, while extremely soft, has a somewhat oily texture (Miller 1907). Figure 1. Big brown bat (Eptesicus fuscus) in Ann Arbor, Michigan. Photo used with permission of the photographer Figure 2. Geographic distribution of Eptesicus fuscus. Phil Myers under a Creative Commons Attribution,(http:// Map used with permission of NatureServe, (http://www. animaldiversity.ummz.umich.edu/site/resources/phil_ natureserve.org/explorer/servlet/NatureServe?searchNa myers/classic/eptesicus_best.jpg/view.html) me=Eptesicus+fuscus). DISTRIBUTION Eptesicus fuscus occurs throughout a large portion of North and Central America and as far south as northwestern South America (Fig. 2). It also resides in Cuba, Jamaica, Puerto Rico (Hall 1981), and some of the Bahama Islands (Buden 1985). The big brown bat occurs throughout the United States except Hawaii (Hall 1981) and in Mexico except the Yucatan Peninsula (Buden 1985). Although there are 11 subspecies of E. fuscus (Neubaum et. al 2007), only E. fuscus fuscus occurs in Mississippi (Hall 1981). FORM AND FUNCTION Form.—Each June, Eptesicus fuscus molts by shedding its winter coat (Phillips 1966). The dental formula is i 2/3, c 1/1, p 1/2, m 3/3, total 32. The crowns on M1 and M2 are narrower than those of M3. The two pectoral mammae contain milk that contains 2.5% lactose, 6.2% protein, and 16.4% fat (Kunz et. al 1983). This species displays pararhinal glands on the sides of the nose that consist of apocrine tubules (for producing sweat), which set atop sebaceous units (Dapson et. al 1977). The red blood cell count is 11.96 x 106/mL (Dunaway Figure 3. Dorsal, ventral and lateral views of the skull and Lewis 1965). The bones that make up and a lateral view of the mandible of an adult female the right and left appendages weigh the same, Eptesicus fuscus in Lexington, Massachusetts. Greatest which indicates that E. fuscus is ambidextrous length of the skull is 18.2 mm. Drawings by J. Love. (Dawson 1975). Polydactyly, deformed Measurements (in mm) of E. fuscus are: total vertebrae, and underdeveloped radii are a length, 87–138; length of tail vertebrae, 34–57; few of the skeletal anomalies that can occur length of hind foot, 8–14; length of ear from in this species (Kunz and Chase 1983). Over notch, 10–20; length of tragus, 6–10; length time, this species has lost the ceratohyal of the of forearm, 39-54; length of third metacarpal, hyoid (Griffi ths 1983). The baculum is about 43-50; length of tibia, 17-21; greatest length 0.8 mm long (Hamilton 1949). E. fuscus will of skull, 15.1–23.0 (Fig.3); zygomatic breadth, defecate within 90–130 minutes of eating. It 11.1–14.2; breadth of braincase, 7.5–9.6; will completely pass a meal within 24 hours of length of maxillary toothrow, 7.0–9.8. Adults eating (Luckens et. al 1971). typically weigh 11-23g. This species is sexually dimorphic, with females slightly larger than Function.—The big brown bat has a large males (Burnett 1983a). The big brown bat and heart that can represent 0.9% of its fat-free the hoary bat (Lasiurus cinereus) are the only body mass. The resting heart rate is about 450 vespertilionids that produce an audible sound beats/min. During fl ight, the heart rate more during fl ight. Wing and skull size is positively than doubles to about 1,022 beats/min (Studier correlated with the amount of environmental and Howell 1969). During torpor, the heart moisture (Burnett 1983b). rate dramatically drops between 4–62 beats/ min. After arousal from hibernation, the heart rate increases from 12–800 beats/min (Rauch 1973). Rhodopsin and an unidentifi ed molecule are females need 105.1 kJ/day (Kurta and Baker the two photopigments in the retina (Kurta 1990). Female big brown bats usually give and Baker 1990). A few ocular abnormalities birth to one pup in the western United States are known to occur, such as an unpigmented and two pups in the eastern United States and choroid, undifferentiated retina, and in Cuba (Barbour and Davis 1969). One theory underdeveloped lenses (Kunz and Chase on why this occurs is that several biogeographic 1983). events resulted in regional separation of ancestral bats. This separation led to several When the ambient temperature is <30ºC, the different mitochondrial DNA (mtDNA) lineages, bat will go into a torpid state. During torpor, which likely resulted in the observed regional the body temperature is between 32 and 36 difference in litter sizes (Neubaum et al. 2007). C (Herreid and Schmidt-Nielsen 1966). If Females can release up to fi ve eggs/ovary overheating occurs, E. fuscus is able to lower (Birney and Baird 1985). Gestation lasts for its core body temperature by dilating blood two months. Young are born from May to July, vessels that lead to the wings (Kluger and with earlier births occurring in lower latitudes Heath 1970). Some bats in this species have (Barbour and Davis 1969). The newborns are been observed panting and spreading saliva altricial at birth and fl edge at 18–35 days (Gould on their bodies when the ambient temperature 1971). The fl edgling’s body mass is about 75% exceeds 40ºC (Kurta and Baker 1990). of adult body mass (Burnett and Kunz 1982). Eptesicus fuscus uses echolocation by sending ECOLOGY out sonar signals to detect prey and avoid Population characteristics.—Eptesicus obstacles. Echolocation is split into three fuscus abundance decreases from the phases: search, approach, and terminal. When deciduous forest biome to the coniferous forest the bat begins hunting it sends out narrow biome (Kurta and Baker 1990). Big brown bats signals at a low rate of 2-5 Hz. Once it detects often live >10 years; the oldest recorded age something of interest, it begins the approach is 19 years (Paradiso and Greenhall 1967). phase where signals increase progressively Males live longer than females. Males occur at from 5–10 to 30 Hz as the bat moves closer to higher elevations in mountainous regions than the target. During the terminal phase, the bat is females (Kurta and Baker 1990). Postnatal almost to its target and emits signals between mortality before weaning is 7–10%. In adults, 100–150 Hz. The sounds in this phase can common mortality factors are predation, failure be heard on a bat detector and are commonly to store enough fat for hibernation, accidents, called the “terminal buzz.” The bat decodes and inclement weather. this acoustic information to determine how close the prey is (Sanderson and Simmons Space use.—Bat-habitat relationships can 2005). be very complicated due to their high mobility. Therefore, studies have failed to quantify ONTOGENY AND REPRODUCTION habitat requirements of Eptesicus fuscus. Eptesicus fuscus copulates between September However, this species occurs in both urban and March (Phillips 1966). However, females and rural areas. Night roosts are frequently in delay ovulation and fertilization until arousal locations that allow it to forage and engage in from hibernation occurs (Kurta and Baker social interactions. Big brown bats frequently 1990). Males are sexually mature by the end use buildings as roosts, often near a light where of their fi rst autumn (Kurta and Baker 1990). insect densities are likely higher. They will also During early stages of pregnancy, females roost in caves, tunnels, mines, tree cavities, accumulate extra fat. During pregnancy, rock crevices, and under bridges (Agosta, females require about 48.9 kJ of assimilated 2002). They seldom move farther than 80 km energy/day to sustain her and her developing between their summer and winter roosts (Kurta young. During the 32–40 lactation period, and Baker 1990). Diet.—Eptesicus fuscus is insectivorous rare (Kurta 1979; Pybus 1986). In this species, (Agosta 2002). Big brown bats are also rabies infects the brain, brown fat, and salivary generalists and do not have a preference for glands (Kurta and Baker 1990) but is not over-water versus over-land foraging sites. transmitted across the placenta (Constantine They begin foraging within an hour after 1986). Incubation of the disease has been sunset and spend an average of 100 min/night observed to last up to 209 days (Moore and foraging. Prey varies by geographic location Raymond 1970).