Part 2-Conservation, Management, Ethics: Buecher-Do Not Disturb Bats 43 Section A-Identifying and Protecting Cave Resources
Do Not Disturb Hibernating Bats or Nursery Colonies Debbie C. Buecher
In the United States, caving has increased in popularity during the last three decades. Unfortunately, human visitation in caves, even by the most conscientious cavers, gradually leaves negative impacts. Because we love our caves there is increasing awareness among the caving community toward performing ongoing restoration or building secure gates to maintain the integrity of caves we visit. However, we must consider the negative implications that our restoration efforts may have on the cave organisms adapted to this unique environment.
Roosting Sites and Nursery Colonies
Bats are extremely intolerant of human intrusion into their roosting sites (Mann and others 2002, Tuttle 1979) and roost disturbance over time can negatively impact population size (Mohr 1972). (See bat sensitivity, page 40.) Some people mistakenly believe that bats can use any cave or portion of a cave as their daily roosting area. Unfortunately this is not the case (Kunz 1982). Bats choose sites because ofa constrained range of tolerant temperature and humidity requirements-conditions that help insure their survival (McNab 1982). There are two extremely critical times in a bat's life when the roosting site is particularly important, during reproduction and during hibernation (Twente 1955). The location where female bats give birth and rear their young is called a maternity roost. For most temperate bat species that use caves, mating occurs in the fall, the bats then hibernatc until late spring, Figure t. Mexican free-tailed bat (Tad- \vhercupon the females begin gestation. Most bats have only one young per arida brasiliensis) year, born in early-to-mid summer (depending on the species). Pups are pups clustered on a totally dependent on "mom's" rich milk for about 4 to 6 weeks (Hill and eave ceiling. Smith 1984). Adult female bats require a warm area of the cave with very high humidity to insure the rapid growth of their nursing (altricial) young (Betts 1997; Williams and Brittingham 1997). Whcn females with young are disturbed, there are two possible scenarios. In one case, the females may attempt to flee with their young pups attached to them. In the panic that ensues, the young that do not already fly (nonvolant) can be dropped onto the floor. Many species of bats have difficulty retrieving a fallen youngster and the pup will perish (McCracken 1989). If the females are successful in 44 Cave Conservation and Restoration
flying with their young, the alternative roosting site they choose may be less optimal for the survival of the young bats. Female bats choose the best site they can find and, barring disturbance from "predatory" humans, they will be loyal to that maternity site their entire lives, as will their daughters, granddaughters, and so on (Hill and Smith 1984; Sidner 1997). Because a maternity colony is particularly vulnerable to disturbance, we There are two must never perform restoration within a maternity site when the bats are in extremely critical residence (American Society of Mammalogists 1992). Fortunately cave times in a bat's life restoration is not usually a seasonally critical activity and can be performed when the roosting when the bats have departed for the season. site is particularly important, during Winter Hibernation reproduction and during hibernation. Another critical period in a bat's life history, when disturbance can reduce survival, is during winter hibernation. When winter arrives and the insects disappear, bats have two options available to them. They can migrate southward to an area where the insects are still somewhat abundant. Or they can sleep (hibernate) through the period of reduced food resources (McNab 1982). Bats that hibernate put on additional fat reserves in the fall in preparation for the winter months of reduced metabolic activity (McNab 1982). Once they are ready to hibernate, bats seek out a roost with an optimally cold but humid microclimate. Different species of bats require different conditions, which is why bats can be found dispersed throughout a cave that is used as a hibernaculum (Hill and Smith 1984; Tuttle and Stevenson 1978). Hibernation in bats is characterized by reduced oxygen consumption, greatly reduced heart rate (approximately 1/40th normal), and a body temperature close to the ambient cave temperature. Under these reduced metabolic rates, the bats slowly draw from their fat reserves and survive the long period of dormancy. Unfortunately, the fat reserves are finite and have evolved to last the necessary period of time the bat is asleep (Thomas 1996). Research shows that even nontactile disturbance (lights, sound, and so on) can trigger a slow arousal in a hibernating bat. It can take upwards of one hour for a bat to awaken enough to fly. In addition, it appears that the arousal of a single bat may disturb other bats asleep in the area, producing a cascading effect from one human disturbance (Thomas 1995). It is in this Figure 2. Indiana bats way that bats '''burn up" critical fat reserves each time they awaken because (Myotis sadaUs) clust- it takes metabolic energy to warm the bat, reserves that were intended to ered on a cave wall. last throughout the winter. e Merlin D. Tullle, Bel Studies show that the metabolic energy required for a single arousal from deep sleep is equivalent to 10 to 30 days of uninterrupted hibernation (Thomas and others 1990). Aller a number of episodes of human disturbance, a bat can literally starve to death before insects are available in the spring. Therefore, arousals can be the greatest factor in depIct- ing hibernation energy budgets (Johnson and others 1998). This is particularly critical for the young of that year. Once pups learn to fly and employ echolocation effectively enough to capture insect prey in flight, it is late enough in the season that it is ollen difficult to store Part 2-Conservation, Management, Ethics: Buecher-Do Not Disturb Bats 45 adequate fat reserves to survive the rigors of hibernation (Thomas and others 1990), In fact, the first winter is such an arduous period for yearlings that there is about 45% mortality for these animals (Sidner 1997), How- ever, for all ages, multiple disturbance episodes can result in overwintering bat mortality due to energy shortfalls, Although conservation and restoration is becoming an important aspect of caving activity in the U.S., we as cavers must always consider the cave life that may be impacted by our efforts, When caving, never jeopardize the bats, invertebrates, or other organisms that dwell in caves-it is truly their habitat that we are invading. It is our obligation to cave responsibly and to be active stewards for the resource. Bats are extremely intolerant of human Cited References intrusion into their American Society of Mammalogists, 1992, Guidelines for the protection of roosting sites, When bat roosts, Journol of Mammalugy 73(3):707-710, cavmg, never Betts BJ, 1997, Microclimate in Hell's Canyon mines used by maternity jeopardize the bats, colonies of Myotis yumanensis, Journaluf Mammalogy 78(4): 1240- invertebrates, or 1250, Brigham RM, 1993, The implications of roost sites for the conservation of other organisms that bats. Provincial Museum of Alberta Natural His/Dry, Occasional Paper dwell in caves-it is Number 19, [Brandon, Manitoba] 19:361-365, truly their habitat Hill JE, Smith JD, 1984, Bats: A Natural HistOlY, Austin (TX): University that we are invading, of Texas Press, 243 p, Johnson SA, Brack Y, Rolley RE, 1998, Overwinter weight loss of Indiana bats (Myotis sodalis) from hibernacula subject to human visitation, American Midland Naturalist 139:255-261, Kunz TH, 1982, Roosting ecology of bats, In: Kunz TH, editor, Ecology uf Bats, New York: Plenum Press, pi-55, Mann SL, Steidl RJ, DaltonYM, 2002, Elfects of cave tours on breeding Myotis velifer, JournalufWildlife Management 66(3):618-624, McCracken GF. 1989, Cave conservation: special problems of bats, National Speleological Society Bulletin 51 :47-51, McNab BK, 1982, Evolutionary alternatives in the physiological ecology , of bats, In: Kunz TH, editor, Ecology of Bats, New York: Plenum Press, p 151-200, Mohr CE, 1972, The status of threatened species of cave-dwelling bats, National Speleological Society Bulletin 34(2):33-47, Sidner RM. 1997. Studies of bats in southeastern Arizona with emphasis on aspects of life history of Antrozous pallidus and Eptesicusfuscus, PhD Thesis, Tucson (AZ): University of Arizona, Thomas DW, Dorais M, Bergeron JM, 1990, Winter energy budgets and cost of arousals for hibernating little brown bats, Myotis lucifugus. Journal of Mammology 71(3):4 75-4 79, Thomas D. 1995. Hibernating bats are sensitive to nontactile human disturbance, Journal of Mamma logy 76(3):940-946, Tuttle MD, Stevenson DE. 1978. Variation in the cave environment and its biological implications, In: Zuber R, Chester J, Rhodes D, editors, National Cave Management Symposium Proceedings: Big Sky, Montana, October 3-7, 1977, Albuquerque (NM): Adobe Press, p 108-12 L Tuttle MD, 1979, Status, causes of decline and management of endangered gray bats, Journal of Wildlife Management 43: 1-17, Twente JW 1955, Some aspects of habitat selection and other behavior of cavern-dwelling bats, Ecology 36:706-732, Williams LM, Brittingham Me. 1997, Selection of maternity roosts by big brown bats, Journal of Wildlife Monagement 6\ (2):359-368, 46 Cave Conservation and Restoration
Additional Reading American Society of Mammalogists. 1992. Guidelines for the protection of bat roosts. Journal of Mammalogy 73(3):707-710. Bat Conservation International (BCI). BCI home page.