Mounting a Bat Skeleton and Summer and Winter Roosting of Little Brown Bats and Big Brown Bats

Jessica Miles

SUNY Cobleskill

Bouck Hall, Box 1037 SUNY Cobleskill

Cobleskill, NY 12043

Abstract

The little brown bat (Myotis lucifugus) and big brown bat (Eptesicus fuscus) are very abundant and their family is seen almost all over the world. Some bats in the Cave House Hotel fit in between a wall in the building, were unable to escape, and perished. The skeleton of one individual was collected and mounted. The finished product will be placed in the Cave House Museum. There are a few possibilities of why the bats were in the wall. They could have formed their maternity colonies or they could have been hibernating. Although there is no way to know exactly what caused the bats to group and climb into the wall, there is a high chance that they had formed a maternity colony based on the location chosen and the number of bats present.

Introduction

History of the Cave House. Howe’s Cave was the third commercial cave opened for tourists in the United States and has been in business for the last 150 yrs (Cudmore 1990). It was open in 1842 by its owner and founder, Lester Howe (Cudmore 1990, Cudmore 2003).

The Cave House Hotel was built for the tourists in 1865 and is still present today (Cudmore 2003). It possesses a very gothic style and is built from limestone. The hotel was built over the entrance to the cave and a cool air passes through the building. It was advertised as the first form of air-conditioning (Cudmore 1990, Cudmore 2003).

The hotel is being renovated into the nonprofit Cave House Museum. It is owned by Cobleskill Stone Products and will display the history of the property and be an educational tool for geology and mining (Cudmore 2003). The bat skeleton will be placed on display in the Cave House Museum.

The deceased bats from which the skeleton was prepared were found inside a wall in the hotel (B. Guenther pers. commun.). It is believed that 100 to 150 bats became trapped inside the wall. There are enough remains to almost completely fill a 5 gal bucket (Cudmore 2003). The workers who found the skeletons could not determine how the bats got into the wall and why they were not able to escape (B. Guenther pers. commun.).

Little Brown Bats and Big Brown Bats. The little brown bat is in the family Vespertilionidae, which contains 275 (Yalden and Morris 1975) to 320 species (Hill and Smith 1986) and is considered to be the most abundant bat in North America (Connor 1960, Creech 1999). This family is one of the most dispersed mammals worldwide. They are seen everywhere except on or in close proximity to the Polar regions (Hill and Smith 1986).

The color variations that may be seen in a little brown bat are pale tan, reddish brown, olive brown, dark yellowish brown or dark brown (Burt 1977, Creech 1999, Hill and Smith 1986). The typical wingspan for a little brown bat is between 222 mm and 269 mm. Little brown bats can live up to about 33 yrs in the wild, but do not do as well in captivity (Creech 1999).

Big brown bats are also in the Vespertilionidae family (Hill and Smith 1986). They are abundant and seen all over the world. Their wingspan is typically 325 mm to 350 mm and they weigh approximately 14 g to 25 g (Fenton 2001, Tuttle 1988). They are a copper color and have no distinctive markings (Tuttle 1988). These bats have been noted to live up to 19 yrs in captivity. In the wild, it is not uncommon to see the bats live to 10 or more years (Fenton 2001).

Both the little brown bat and the big brown bat are nocturnal (Burt 1977, Searfoss 1995). Since bats do not need exceptional vision, it is believed they are color blind (Yalden and Morris 1975). Both species are insectivorous (Fenton 2001, Tuttle 1988, Yalden and Morris 1975). An insectivorous species is a more primitive bat, compared to the carnivorous bats which eat small rodents, frogs, and salamanders (Yalden and Morris 1975). Ratcliffe and Dawson (2003) found that little brown bats are able to catch their prey in the air or catch it like a hawk by swooping down when the prey is not suspecting it. Once daylight hits, they find a dark place and hang upside down to digest their food (Burt 1977, Searfoss 1995). Bats eat about 1g of insects in 1 hr, which is approximately 500 individual specimens. Big brown bats every night will eat 50% to 100% of their body mass in insects (Fenton 2001). An insect diet forces these bats to hibernate in the winter due to the lack of availability of food (Hill and Smith 1986, Yalden and Morris 1975).

Little brown bats are a monoestrous species meaning that they have one reproductive period per year and only produce a single young in each litter (Fenton 1983, Yalden and Morris 1975). Big brown bats usually give birth to twins (Fenton 2001, Tuttle 1988). Females give birth in mid-June in little brown bats and in late May through June in big brown bats (Fenton 2001, Fenton 1983). Little brown bats usually start to fly 18 to 21 days after birth (Fenton 1983) and 18 to 35 days for big brown bats (Fenton 2001).

Mating occurs in late August and early September while ovulation occurs in late March and early April (Fenton 2001, Fenton 1983). Breeding in these bats is onset by the decrease in light and decrease in temperature (Fenton 1983, Yalden and Morris 1975) and is closely followed by the beginning of hibernation (Fenton 1983).

Rabies is a concern with bats, but human cases of rabies in the United States are rare. Most people who contract rabies get it through a bat bite, but the bite marks are so small, most people do not even realize that they have been bitten (Jackson and Fenton 2001, Moran 2002). Moran (2002) stated that the death rate from rabies worldwide is a mere 0.002 death per 100,000 rabies cases. Big brown bats are blamed for most bat bites because when handled, these bats will usually bite in self-defense (Fenton 2001).

Study Area

A majority of the work on the bat skeleton took place in either the Home Economics building or Wieting Hall, both on the SUNY Cobleskill campus. SUNY Cobleskill is in Cobleskill, New York in Schoharie County. The latitude and longitude is 42.67° North, 74.48° West. The elevation of Cobleskill is 932 ft. There are no specific conditions in which a bat skeleton can be prepared. More arid conditions are preferable for faster and more efficient drying.

Methods

The bat carcass was placed in water that was at room temperature. After approximately 15 min., the skeleton was removed and using forceps, the skin was carefully pulled away from the bones. This procedure was repeated until a majority of the larger pieces of flesh were detached (Schmid 1972) and disposed of. A dissecting microscope aided in carefully removing small pieces of flesh, especially around the teeth, ribs, and wings. The ligamentary skeleton preparation described by Schmid (1972) was used due to the small size of the mammal. The bat’s ligaments were kept intact to keep the bones in proper place (Schmid 1972). Hydrogen peroxide (30%) whitened and sterilized the bones (K. Berner pers. commun., S. Samolis pers. commun.). The skeleton was kept in the solution for at least 24 hrs (S. Samolis pers. commun.). Once the skeleton was dried and rinsed with room temperature water, the skeleton was placed in ammonia and water in a 16 oz/gal concentration over night to remove any brown and bloody spots (K. Berner pers. commun.). After this period, the skeleton was rinsed to remove remnants of the solution. While the ligaments were saturated, the skeleton was stretched (Schmid 1972) into a position where both sides were in a symmetric pattern and easy to observe (Anderson 1968). Anderson (1968) also noted that by spreading each finger of the wing, measurements and more observations could be drawn from the bat skeleton. Cork and pins were used to secure the bones in the desired position and left to dry for several hours (Anderson 1968). Epoxy glue on the tip of a pin glued any bones back in place and reinforced weak joints (S. Samolis pers. commun.). Black, 2mm thick foam was used to mount the bat on a secure material. The bat was sewed down to the foam using a fine, clear thread The foam was cut into the shape of the inside of the box and duplicated four times. After the bat was sewed down to one piece, epoxy was used to glue all the pieces together to form one thick piece of foam. The mass of foam was glued to the glass and then the glass top was glued down to the box.

Discussion

There are several reasons why the bats could have become trapped inside the wall and were not able to escape. Although the facts will remain unknown, there are a few justifications for why the bats may have been inside the wall.

One reason could be that in the summer months, bats prefer hot areas with extreme temperatures that could be as hot as 131°F (Creech 1999, Yalden and Morris 1975). These colonies are often seen in buildings, especially in the attics and roofs (Connor 1960, Creech 1999, Yalden and Morris 1975). Big brown bats particularly like attics, eaves, and the insides of walls (Fenton 2001). They are called maternity colonies and usually form in April and May (Creech 1999, Davis and Whitaker 2002).

The colonies are chiefly made of females and young (Creech 1999, Fenton 1983, Walker 1975, Yalden and Morris 1975). These colonies can be a few bats up to as many as 1000 bats (Creech 1999, Walker 1975, Yalden and Morris 1975). The females stay in close groups to increase the temperature of the roost. This is thought to help the young grow at a faster rate (Fenton 1983). They also prefer extremely hot conditions to keep the young bats warm because at an early age they are hairless (Yalden and Morris 1975).

Henry et al. (2002) found that expectant mothers do not travel far from the roosts, but do not usually return during the night. They then found that lactating mothers return 1 to 2 times during the night to feed their young. So the actual home range of pregnant and lactating mothers decreases by 51% and their average flight range decreases by 35%.

The males during this time are found in other places away from the colonies because they do not participate in the raising of the young (Fenton 1983, Yalden and Morris 1975). Males also prefer to find cooler areas to slow their metabolisms and conserve energy (Fenton 1983).

Another possible reason could have been hibernation during the winter months. If the bats were little brown bats, this is unlikely because they prefer caves in the winter where there is a more steady temperature and humid conditions (Creech 1999, Fenton 2001, Hill and Smith 1986, Yalden and Morris 1975). Humidity is important because it keeps the bats hydrated. Little brown bats lose water when they are breathing, so the high humidity helps them to retain water. Also, staying in tight clusters helps to reduce the amount of water lost by each individual (Fenton 2001).

Big brown bats are the opposite. They are able to withstand fluctuating temperatures, even temperatures below freezing. They also like to have very dry conditions compared to little brown bats. They spend the winters in walls in more severe winter climates (Fenton 2001).

Once bats move into their hibernation areas, they are usually in low concentrations compared to the maternity colonies in the summer (Connor 1960). In most cases, the males are in tight clusters while the females are alone or in small groups (Fenton 1983). The bats are aroused from hibernation once there is a moderation in temperature (Yalden and Morris 1975).

Connor (1960) felt that there is a small possibility that little brown bats would remain in buildings all winter. Although this is a possibility, he felt that the chances were small because caves provided a more adequate hibernating environment because of the constancy in temperature and high humidity. The walls would not keep the temperature stable enough for the little brown bats to survive. If the bats were on the warmer side of the insulation, their temperature would be too high and their bodies too active which would result in them losing their body fat supply. If the little brown bat was on the colder side of the insulation, its energy would be expended shivering to keep warm (Fenton 2001).

It seems that most likely, if the bat is a little brown bat, it climbed into the wall to roost and form a maternity colony. Somehow the group became trapped in the walls and perished. If it was a maternity colony, the prepared skeleton would more than likely have been a female little brown bat because it is a full-sized bat and there would be few to no adult males trapped in the wall.

Based on the information, if the skeleton was a big brown bat, it too was probably making a maternity roost. This is concluded because of the multitude of carcasses found. There is the possibility that a few over a period of time, some would go into the wall to hibernate and perish and then more would do the same. This seems very unlikely because big brown bats prefer to hibernate alone or in small groups (Fenton 2001, Tuttle 1988).

One problem that arose from this project was that the identification of the bat is still unknown because it is difficult to accurately see the skull in the box. A proper identification before completing the mount would be a great help to the procedure.

Acknowledgements

I would like to thank Mr. Ben Guenther who supplied the skeleton. Mr. Scott Samolis gave advice on the preparation of the skeleton and donated the box to mount it in. Mr. Kevin Berner brought the skeleton to me and has helped in its identification. I would also like to thank my mother for helping me mount the bat.

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