The Ozark Big Eared Bat
The Ozark Big Eared Bats (Corynorhinus townsendii ingens) are found in different habitats accross the United States. They are limited in number and are found in Missouri, Arkansas, Oklahoma; however, it was reported that they are no longer found in Missouri because of the destruction of the environment. In Oklahoma, they are found in Adair County and adjacent parts of Cherokee and Delaware counties. In the early 1970s, the Ozark big eared bats were documented to only be a hundred in Missouri. With efforts in the l980s, it was reported that an increase in number among these creatures have occurred. The Ozark big eared bats were estimated to be around 450 to 1700 individuals. This amount came to a near double in the 1990s having 1600 to 2300 individuals in number.
The Corynorhinus townsendii ingens is a member of the the order Chiroptera of class Mammalia under the phylum Chordata of Animal kingdom. On further classification of order Chiroptera, Ozark big-eared bat belongs to suborder Microchiroptera. These bats belong to genus Corynorhinus and townsendii species of Vespertilionidae family. Ozark big-eared bat is further classified to subspecies ingens.
Ozark Big Eared Bats are medium sized bats with broad wings. They have glands on either sides of their muzzle. The snout is short with elongated nostrils. They normally have a body of less than four inches and have ears measuring to more than an inch. The Ozark big eared bat’s ears are positioned erect except in hibernation when they coil their ears like a ram’s horn (National Geographic, n.d.). Aside from the ears, these creatures have two distinct facial glands on their nose. Their fur is light to dark brown and their stomach is tan (National Geographic, n.d.). They also have a wingspan ranging from 12 to13 inches. Lifespan of wild individuals is about 21 years. During the summer, both sexes occupy separate roosting locations. Males live solitary lifestyles. Maternal colonies are formed by females, where they live with their pups. Pups are accustomed to food at the age of six weeks and shortly after that they become mature bats. When winter arrives, these bats hibernate, which occurs in closely packed clusters.
Although the Ozark Big Eared Bats is ranked “apparently secure” globally, they still have a low tolerance when it comes to human disturbances. Human presence in their environments can be stressful for these creatures such that it turns out to be very fatal for them. Not only those, populations of these creatures who choose to roost in abandoned mines are threatened by demolitions. Bats who are affected by the demolition are buried alive inside the caves.
Another concern now is that these bats are also threatened by a disease called the white nose syndrome. This fungal disease has overwhelmed bat populations since 2007. This fungus grows in cold, humid conditions that are found in caves. This fungus grows on and invades the bodies of bats that are currently hibernating.
Ozark Big Eared Bats are now considered endangered because of suffering greatly from great human disturbances like commercialization and exploration within their habitats. These species only have enough fat to last them until spring. That’s why when people disturb caves bats will be forced to burn their stored up energy for hibernation. If this happens, these bats will starve until their death even before spring arrives just in time for their feeding period.
If these bats are left at a high mortality rate, human will lose their gains from these creatures. One importance of this is the bat’s use for pest control. They are very effective predators of pests especially moths. This phenomenon results to less environmental and agricultural damage that are caused by pests. Despite the positive effects of these creatures, they also carry around dangerous effects for people. These bats carry around rabies and histoplasmosis that may harm humans. However, infecting humans are quite uncommon. They also carry around bacteria, fungi and viral and mycotic means that may also be harmful to man. The Center for Disease Control (2001) stated that 17.2% of rabies cases documented were caused by bats. But, this is not always the case since the Corynorhinus townsendii do not live in populations near humans since being around human population could harm the people by surrounding humans with feces, parasites and bacteria. Sanitation and health of the humans would be the main concern if bats lived anywhere near the human population. A more popular concern would be the noise that the colonies produce. This goes along with the inconvenience brought about by the accumulated fecal matters.
After discussing the unique characteristics of these creatures, let’s now move on to how the Ozark Big Eared Bats forage for food.
Foraging Ecology
The Ozark Big Eared Bat feed primarily on moths and insects. They are late flyers. They fly late at night to feed. Like other bats, the Ozark Big Eared Bat has special sensory organs that allow it to locate prey without seeing them. The bat sends out a high-pitched sound which is too high for humans to hear and the sound waves bounce off solid structures. The waves return to the bat that uses its sensory organs to determine whether the object is food (i.e. an insect) or other. When it determines it is an insect it can filter out all other signals, focus on that particular signal and quickly locate, fly to and consume the bug. Although the bat is small, it consumes a large number of insects each night meaning that the sensory organs responding to the sound waves have to be very advanced. They form roosts for up to 30 minutes before sunset, often testing the lights. They begin to exit the roosts approximately 26 to 60 minutes after dark (Loeb et. al., 2010). Navigation and perception in this species is conducted by echolocation (Gruver & Keinath, 2006). They hunt during the night to use their echolocation abilities to locate their prey and also to avoid trees and other obstacles. They prey off tree branches and drink on surfaces of ponds and pools. After eating, they return to night roosts to digest and then make a second trip for eating.
Foraging areas are consistently found within hardwood forests or pine forests. According to a study made by Lacki and Dodd (2011), males fly farther distances than its female counterparts.
The nocturnal habits, ability to fly, and their occupation of difficult to find roosting areas make them an unlikely prey for predators.
When it determines it is an insect it can filter out all other signals, focus on that particular signal and quickly locate, fly to and consume the bug. Although the bat is small, it consumes a large number of insects each night meaning that the sensory organs responding to the sound waves have to be very advanced. In addition, Ozark bats hunt later in the night than most other bats such that they must be able to use their echolocation abilities not just to locate pray but also to avoid trees and other obstacles as well as other bats who are also out hunting.
Reproductive Ecology
During the summer, adult males begin spermatogenesis reaching their peak in September. On the other hand, females experience a proestrus during this season. These big eared bats mate with different partners repeatedly during the mating season. The Big Eared Bats are k-selected. They only have one offspring per pregnancy. The male young-of-the-year is only capable of producing small amounts of sperm. The low amount of sperm together with the small glands prevents the bats from being able to produce their first “fall.” Females on the other hand, are capable of pregnancy during their first year. During autumn, copulation begins. Females mate before they reach the hibernacula or the peak during hibernation in November through February. Gestation among these mammals lasts from 56 to 100 days. The young is born during a 3 to 5 week period starting from late May, and adult females normally deliver before younger females (Schmidt, 2003).
It is estimated that only 50% is the expected survivorship among the young from its year of birth to the next and it is estimated that only 80% is the expected survivorship among adults. Schmidt (2003) suggests that the mortality of the young of the year occurred before hibernation.
There are several limiting factors found that limit the capacity of the bats to reproduce. Schmidt (2003) suggested that roosting sites with inadequate food supply limited the population of the Ozark big eared bats. Another limiting factor discussed by Schmidt (2003) is the winter mortality because of lack of sites for hibernation to provide stable conditions throughout the winter. It is also apparent among these creatures that they are loyal to their roosting sites. They return yearly to the same maternity roost thus there is the absence of migration.
Male bats do a short mating display during which they approach a female making a loud noise. If the female accepts them, the male rubs its snout over the female’s neck, forearms and face. The glands on the male’s snout functions as a detector to find the female’s scent before copulating; during this time, female bats are in a state of lethargy.
Young bats are born naked and their ears are folded over their eyes for several days. They also cling to their mothers during the day and form clusters when the mothers leave at night to forage.
These bats are expected to have a great potential for longevity. Bat individuals belonging to this specie have been said to live at over twenty years and have higher mortality rates among the young. It is said that if the young can survive their first year, their chances of survival goes up. If kept in captivity, the life expectancy of these creatures become shorter.
Habitat
Most individuals from the Corynorhinus townsendii ingens population live in montane forests. These forests are filled with thick oak hickory trees and are bounded by shrubs and grasslands. The habitat for the Ozark Big-eared Bats are limestone caves in wooded areas of the Ozark Highlands. The associated biome is temperate deciduous forest.
These creatures choose roosting sites that are common in caves, cliffs and rock ledges but they are found in abandoned mines and other man-made structures. They normally choose cold places for roosting, and they choose their hibernacula with only an acceptable amount of air movement. Abandoned buildings are used only in summer while caves and mines are chosen during the winter. Roosting sites have open ceilings because these bats don’t crawl well. They opt for habitats that are dark and those that are sensitive to human activity. If determined that there is human activity, these bats are caused to relocate to look for better roosting sites. They occupy the part of the cave that’s near the entrance. They are not migratory but they move from different caves in between seasons. When looking for food, they fly above trees and in gaps and clearings within forests.
Oklahoma supports 1,600 to 1,800 bats. In 1995, ten caves in Adair and Delaware counties, Oklahoma were recorded as important caves for the Ozark big eared bats. Forty caves are identified as “transient caves” and eight are identified as possible caves for their use. These bats prefer caves in limestone karst formations that are found in places with mature hickory, beech, maple, and hemlock trees. Caves for maternity are places where the females nurture and bear their young are closer to food sources than the hibernation caves. Hibernation caves on the other hand are caves which are the best places as protection from cold and wind.
Other Behaviors
Bats also exhibit behavior that is only unique to their kind. The composition in population varies according to the current season. Female bats create nursery colonies during the summer and males are solitary. There are times when both males and females live in the same group, despite the fact that they don’t normally form groups together. There are no concrete evidences yet on how nursery colonies are formed but females don’t leave to form new groups. The entire population move from one group to another.
Sizes among bats vary by region. In the east, groups have up to 1,000 or more individuals. Roost sites are in an area with dim to no light at all. Their choice for a low light or total darkness place shows in their eating behaviors. These creatures don’t leave their roosts to look for food until very late in the evening. Their clusters are never found in crevices because they don’t crawl away from their current places. They are found clustering on spaces with open ceilings. They often hang on ceilings by using just one foot. While sleeping, their ears coil over their heads like a ram’s horn. They are light sleepers thus making them easily disturbed and if disturbed they immediately relocate away from the disturbed area.
These bats are flexible flyers. They exhibit movements that are darting to hovering actions. When landing, the bat swoops from below then folds its wings and quickly flips over and grasps onto the surface with its foot. These species are experts in avoiding traps and are species that that are hard to put in captivity.
One of the most difficult relationships to understand in the colony is the mother-young relationship. In the day, young individuals in the colonies cling to their mothers. But, when mothers look for food at night, young individuals in the clusters remain in groups. Mothers can identify their young by using auditory signals ad it’s been theorized that mothers use their snout to identify the smell of their young. These species do not migrate in long distances. Within the range, these bats move to different roosts.
Navigation and perception in these species is guided by the bat’s ability to echolocate. The large ears of these bats show low frequency echolocation calls and use their sensitivity instead reflect the low-frequency echolocation signals that they use to determine sounds. These bats can move their ears to concentrate on a moving source of sound. Echolocation is attained by releasing intense sounds in the larynx. Not like other mammals, whose auditory organs are connected to the skull, the bats’ auditory organs are encircled with fatty substances or sinuses. They dampen the construction of sounds from the larynx. The middle part of the ear muscles contract before sonar pulses so that the noises that these bats produced are easily absorbed. High Pitched sounds are produced ranging from a couple of hundred pulses per second. These bats send out low frequency pulses having longer durations until they locate a food. After locating the insect, pulse rate of these animals increase and shortened and the pitch is then lowered to help locate the insect.
When the pulse identifies an obstacle, it bounces back towards the bat so that the bat can determine its shape, distance, movement and texture. Not only do auditory perceptions play an important role in foraging, they also play an important role in social interactions as well. An example of this would be that low frequency sounds (those under 20 kHz) are acceptable sounds to recognize humans and social interactions; these include spacing within colonies, communication, interaction between the mother and its young and warning calls. When performing a display of courtship, males make high pitched twittering noises to their female choice. Young bats produce calls that are unique to help their mothers locate them easily in the event of being separated with the colony. Over time, these calls from the young develop and become chirping noises. Olfactory signals play a important role in the lives of these bats to recognize a colony and also for mother and child recognition. These acoustic emissions are essential in the recognition of the mother and its child especially during cases when the child is beyond the range of olfactory reaction. Males on the other hand are observed to be “scent marking” the females before copulating using excretions from the glands near the nozzle.
Bats are the only group of mammals who have developed true, self-powered flight. In order to achieve this they developed modified forelimbs, which are capable of supporting the wing membranes (patagium). While the bats limbs resemble other mammalian limbs there are different bone to muscle ratios in the bat compared to non-flying mammals. The hands and fingers are the most lengthened structures of the limb. These bones are the primary supports for the wing membranes and allow the bat to control its flight. The wing membrane extends across the bats fingers and is affixed to the side or back and the lower portion of the leg. Part of the patagium stretches between the posterior limbs. There are many blood vessels and nerves found throughout the patagium. To give them the strength to fly, Bats have also developed five unique muscles within the wing membrane. They also use other chest and back muscles to enable them to move their wings at a high speed to maintain flight
Evolutionary differences between birds and bats are evident on sight. The clearest factor, which differentiates bat wings and bird wings, is that bats wings are composed entirely of membrane while bird wings are composed of feathers. While birds have a lengthened arm to help support their wings, they do not have lengthened fingers because they are not necessary for their wing structure. Another difference is that the muscles used to power the wings in birds are found exclusively in their chests while for bats these muscles are found along their backs. (Fenton, 1983).
The way the rear limbs are oriented also help support the wing membrane. They are rotated 90 degrees from the hip such that the knees are turned backwards causing an awkward walking motion. However, this adaptation provides enormous benefits in helping support the large wing membranes and in allowing the bat to hang upside down with special tendons that lock the claws into place to allow the bat to sleep in this position.
Ozark big-eared bats are prone to genetic drift and inbreeding because of their small population size. In spite of their low population, there is diversity in their mitochondrial and nuclear genomes. A latest phylogenetic study provides evidence to re-elevate Corynorhinus to generic level and distinguish Corynorhinus from the Old World genera Plecotus (Gruver & Keinath, 2006).
So what can we do to protect these one of a kind species? First, we should not enter gated caves, and mines with signage that indicate that it is used by endangered bats. Second, we should all avoid being sources of disturbance for these creatures because disturbing them lower their chances of survival thus increasing their mortality rate. Without these bats, we will no longer have insect specialists lurking around our forests. Pests and insects will increase and a balance in ecology is lost. Another thing that we can do is to check on abandoned sites before demolishing them and putting them to the ground. Many of these creatures are just left inside before blowing it all up. That’s why many of these bats are just left alone to die inside the man made mines and caves.
References
Arkansas Game and Fish Commission Strategic Non-game Management Plan. (n.d.). Prepared
Currie, R. (2000). Federally listed threatened and endangered species of concern to mining.
Paper presented at Bat Conservation and Mining: A Technical and Interactive Forum, November 14-16, St. Louis, MO.
Fenton, M. B. (1983). Just Bats. Toronto: University of Toronto Press.
U.S. Fish and Wildlife Service (1995). Ozark Big-Eared Bat Corynorhinus townsendii ingens
(Handley) Revised Recovery Plan. Tulsa, OK.
Gruver, J., & Keinath, D. (2006, October 25). Townsend’s Big-eared Bat (Corynorhinus
townsendii):A Technical Conservation Assessment [PDF document]. Retrieved from
http://www.fs.fed.us/r2/projects/scp/assessments/townsendsbigearedbat.pdf
Loeb S. C., Lacki, M. J., Miller, D. A. (2010). Conservation and Management of Eastern Big-eared Bats: A Symposium. Retrieved from http://rafbat.org/gtr_srs145.pdf.
Ozark Big Eared Bat. (n.d.). National Geographic. Retrieved from http://animals.nationalgeographic.com/animals/mammals/ozark-big-eared-bat/
Sullivan, J. (2009). Corynorhinus townsendii Townsend's big-eared bat. Retrieved from http://animaldiversity.ummz.umich.edu/accounts/Corynorhinus_townsendii/#behavior
Schmidt, C. (2003). Conservation Assessment for the Townsend’s Big Eared Bat in the Black Hills National Forest South Dakota and Wyoming. United States Department of Agriculture. Retrieved from http://www.fs.usda.gov/Internet/FSE_DOCUMENTS/fsm9_012119.pdf
United States Fish and Wildlife Service (2011). Ozark Big-eared Bat. Retrieved from http://www.fws.gov/southwest/es/oklahoma/Documents/TE_Species/Species%20Profile /Ozark%20Big%20Eared%20Bat.pdf
Weyandt, S., Bussche, R., Hamilton, M., & Leslie, D. (2005). UNRAVELING THE EFFECTS
OF SEX AND DISPERSAL: OZARK BIG-EARED BAT (CORYNORHINUS TOWNSENDII INGENS) CONSERVATION GENETICS [PDF document]. Retrieved from
http://www.mammalsociety.org/uploads/Weyandt%20et%20al%202005.pdf
