Plecotus auritus

The Brown Long-Eared Bat

Taxonomy

Plecotus auritus, also known as the brown long-eared bat, belongs to the family Vespertilionidae of the order Chiroptera. Specifically, the species is classified among the microchiroptera bats.

Geographical Distribution

The species is widespread in Europe, with the exception of southern Spain, southern Italy, and Greece. It is the second most common species of bat in Britain, although it is absent from north and northwest Scotland. The animal can also be found in India, Nepal, Mongolia, Siberia, China, Sakhalin, Japan, South Korea, and the Himalayas.

Physical Characteristics

The average head-body length is approximately 37 to 48 millimeters, and the wingspan ranges from 230-285 millimeters. The body weight of the animal normally ranges from 5 to 12 grams. The females of the species are slightly larger and heavier than the males. The adult bat has brown fur with a pale underside and a pink-brown face, while juveniles are more gray in color overall. P. auritus have relatively large eyes, and slit-shaped nostrils that open laterally. The most distinguishing features are the animalπs ears, which are nearly the length of its whole body. When extended, the ear can be up to 25 millimeters long. At rest, their ears are tucked back and folded, resembling ram horns. When the animal hibernates, the ears are tucked back so far that only the tragus is visible.

Habitat

The general habitat of P. auritus is in sheltered valleys and mountainous woodland. In the summer, the species roosts in barns, hollow trees, and old buildings. In the winter, it can be found hibernating in caves, mineshafts, hollow trees, and underground sites.

Roosting Behavior

Roosts provide the bats shelter from the weather, protection from predators, and a warm environment for rearing their young. Colonies typically consist of 10-20 adults, but can contain as many as 50 individuals. Entwistle (1994) found that in May, the bat colonies of the species were nearly all female, but the number of males increased from June to September with a decease in the number of females and juveniles. By October, males dominated the colonies. However, females tend to remain in one roost all their lives, while males are more likely to depart to another roost.

Diet and Foraging Behavior

The species is insectivorous, and feeds primarily on moths. They also eat caterpillars, spiders, earwigs, dung beetles, and flies. They forage at night, usually relatively close to their roost. Foraging usually ends after about 4 or 5 hours. The bat catches insects in flight or by foliage gleaning - picking insects out of trees or off the ground. Gleaning is advantageous over aerial capture because moths cannot as easily detect the bats presence so gleaning bats eats more moths than do aerial hunters. Additionally, gleaners are less dependent on air temperature and also they can catch non-flying prey like spiders and caterpillars. Aerial hunters catch insects directly in their mouth, but also can use the tail and wing membranes to scoop up moths or corral the insect toward the mouth. Also, Plecotus auritus sometimes perform steep somersaults techniques to catch prey. Plecotus bats not only fly in straight horizontal paths, but also are known to hover, especially when gleaning for food from vegetation or tree trunks. Figure 1 represents each type of flight.

Fig 1. Flight of the long-eared bat, Plecotus auritus. The position of the wings at each of four 10-ms intervals is indicated by the numbers 1-4 on the dashed line. This diagram represents the path taken by the wings during horizontal flight (top, flight speed = 2.35 m/s) and hovering flight (bottom, flight speed = 0). (Norberg, 1976)

Hibernation

Prior to hibernation, in late summer, the bats accumulate fat and this is used as an energy store for the winter. Hibernation begins in November and ends in late March. When the bat is hibernating, the wings are folded around its body, with its ears tucked under. Plecotus auritus typically hibernates in caves, tunnels, mines, buildings, and tree holes. The animals prefer to hibernate at very cold temperatures, just above freezing. They hibernate solitarily or in small groups. Premature disturbance of hibernating bats can cause decreases in their population because it arousal causes them to use up energy resources and in consequence they may run out of energy and die before the end of winter. As a result, biologists and tourists are restricted in how they observe the bats.

Mating Behavior

The male brown long-eared bat has facial glands which produce a brown, odorous secretion used to mark potential mating roosts. The male visits as many roosts as possible to maximize its chances of mating, and marking roosts helps to advertise their presence in order to attract females. P. auritus is considered to show random, promiscuous mating, where swarming occurs and females mate with many males.

Reproduction

The reproductive cycle of the brown long-eared bat is long - spermatozoa produced in one summer do not result in live young until the following summer. Males produce the greatest amount of sperm in late August/September and the mating period typically begins in October. Mating continues sporadically throughout the winter, but the maleπs sperm production ceases in November. Females delay fertilization until late April or May, after hibernation ends. This is when the female begins ovulation and sperm stored in the uterus fertilizes the ovum. The females then move into nursery roots (maternity colonies) and parturition takes place, usually in early July. The female gives birth to only one offspring per year (the length of one breeding season); twins are very rare. Because the reproductive cycle is long, complex, and only yields one infant, a female whose baby dies loses it chance to reproduce for a whole year. Fortunately, the species has evolved adaptations to minimize such failures, and studies have found that 70% (Entwistle, 1994) to 97% (Benzal, 1991) do produce young each year.

Long-eared bats are born hairless, pink in color, and with their eyes closed. In the first week of its life, the infant bat clings to its mother nipple. The baby is born with incisors that have hooked tips to enable the animal to grip the nipple, even when the mother is in flight. When the mother forages, the newborn bat is left clinging to beams in the roost. By 4 days old, the baby has a covering of hair and at 6 days old, the ears become erect and the eyes open. By 10-12 days, babies begin to groom themselves and flap their wings. After 20 days, they can fly around the roost, and by day 35, they first leave the roost on their own wings. Weaning of the infant is complete about six weeks after birth.

The male Plecotus auritus reaches sexual maturity in the second summer of their life. The female is sexually mature anywhere from 24-36 months of age. The maximum age for the species is 30 years, but the average life span is seven years for males, sixteen for females.

Echolocation

Because the echolocation calls of Plecotus auritus are very quiet, these bats are known as "whispering bats". I. Ahlen (1981) described the calls as faint and short FM sweeps, about 2 ms long, and with prominent second harmonics. Using quiet calls is beneficial to the animal because the prey is less likely to detect its presence. The frequency of the brown long-eared batπs call is usually 83-26 kHz, but sometimes louder at 42-12 kHz. Figure 2 represents a loud-long sweep produced by Plecotus auritus.

Fig 2. Diagrammatic representation of the loud-long sweep (Ahlen, 1981) of P. auritus

In general, CF signals, which increase the range of target detection, are used by the bats for hunting in open areas, while FM signals allow them to more accurately locate obstacles and targets in cluttered environments. Hence, gleaning bats use short, low-intensity FM signals to distinguish between insects and foliage while foraging.

Predation and Parasites

The habit of the brown long-eared bat to fly close to the ground makes it vulnerable to attack by predators, especially the domestic cat, Felis catus. Other predators include the barn owl (Tyto alba), the tawny owl (Strix aluco), and the kestrel (Falco tinnunculus).

Plecotus harbor relatively few ectoparasites, especially the adults. This is believed to be connected with small colony size in these bats, since fleas and mites cannot be transferred as easily. Also, the batπs tendency to move from roost to roost further reduced the opportunity for parasite populations to increase. As for internal parasites, Gardner et al. (1987) examined blood smears of P. auritus and found only one bacterium, Grahamella, which is transmitted by fleas and not harmful to the host.

Relationship With Humans

P. auritus is considered to be very docile and one of the easiest European species to handle and to tame. Their lives are greatly entwined with those of human beings, as they utilize human homes and mine shafts for shelter and protection. However, humans are more of a threat than a positive influence to these bats. The most serious problem this species faces is the loss of deciduous woodland due to large-scale farming. Other threats include barbed wire, which bats can be impaled upon during foraging, deliberate destruction of roots by pest exterminators, and disturbance from hibernation.

Plecotus auritus is not considered to be an endangered species, but that does not mean it is without protection under the law. In Britain, bats are protected under the Wildlife and Countryside Act of 1981, which states it is illegal for anyone without a license to intentionally injure, kill, or even handle a bat, to possess or try to sell a bat, or to disturb a roosting bat. Europeans even set up bat boxes, or artificial roosts similar to bird nesting boxes, for the bats to use. These bat boxes are popular with both the public and bat enthusiasts because they are a practical method of protecting bats and keeping them from intruding human homes.

Bibliography

Ahlen, I. (1981). Identification of Scandinativan bats by their sounds. Report No. 6, Dept. Wildlife Ecol. Swedish Univ. Agric.Sci.

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

Benzal, J. (1991). Population dynamics of the brown long-eared bat (Plecotus auritus) occupying bird boxes in a pine forest planation in central Spain. Neth. J. Zool., 41 (4): 241-249

Entwistle, A.C. (1994). Roost ecology of the brown long-eared bat (Plecotus auritus) in northeast Scotland. Unpublished PhD thesis, University of Aberdeen, UK

Fenton, M. Brock, Just Bats. Toronto: University of Toronto Press, 1983

Gardner, R.A., Molyneux, D.H. and Stebbings, R.E. (1987). Studies on the prevalence of haematozoa of British bats. Mamm. Rev., 17 (2/3): 75-80

Neuweiler, Gerhard. The Biology of Bats. New York: Oxford University Press Inc, 2000

Norberg, U.M. (1976). Aerodynamics, kinematics, and energetics of horizontal flapping flight in the long-eared bat, Plecotus auritus. J. Exp Biol. 65:179-212

Norberg, U.M. (1976). Aerodynamics of hovering flight in the long-eared bat, Plecotus auritus. J. Exp Biol. 65: 459-470

Nowak, Ronald M. Walkerπs Bats of the World. Baltimore: Johns Hopkins University Press, 1994

Swift, Susan M. Long-Eared Bats. London: T&AD Poyser Ltd, 1998