Internal Cave Gating As a Means of Protecting Cave-Dwelling Bat

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CAVE-GATING PROTECTING BAT POPULATIONS 133 Internal Cave Gating as a Means of Protecting Cave-Dwell- ing Bat Populations in Eastern Oklahoma

Keith W. Martin Department of Math and Science, Rogers State University, Claremore, OK 74017

William L. Puckette Poteau Public Schools, Poteau, OK 74953

Steve L. Hensley Ecological Services Office, U.S. Fish and Wildlife Service, Tulsa, OK 74127

David M. Leslie, Jr. Oklahoma Cooperative Fish and Wildlife Research Unit, U.S.G.S. Biological Resources Division, Oklahoma State University, Stillwater, OK 74078

INTRODUCTION

Of the 45 species of bats found in North induce elevated mortality rates, poor recruit- America, about 18 rely substantially on caves ment, and actual colony abandonment. At throughout the year. Thirteen of these spe- hibernacula, premature arousal from bouts cies are obligate cave-dwelling bats using of torpor and hibernation ultimately con- caves year-round. They use caves as winter sume stored energy reserves. Disturbance hibernacula, stop-over roost sites during at maternity colonies adversely affects ther- migration, summer roost sites, or maternity moregulatory requirements of non-volant sites where adult females give birth to their developing young (2,7,11-13). Low repro- young. A general correlation has been made ductive rates, long generation times, and between the degree to which a species is re- concentrations of populations in localized liant on caves during its life cycle and con- roosts are life-history characteristics indica- sideration as an endangered or threatened tive of North American cave-dwelling bats. species by the U.S. Fish and Wildlife Service. Such life histories and adverse effects of hu- All North American bats listed as endan- man disturbance present difficult challenges gered or threatened by the U.S. Fish and as wildlife managers and bat conservation- Wildlife Service are cave-dwelling species or ists develop management objectives for pro- subspecies (1-3). Two cave-dwelling species, tecting and recovering declining bat popu- the gray bat (Myotis grisescens) and Indiana lations. Bat (Myotis sodalis), and one subspecies, the Contemporary efforts for bat conserva- Ozark big-eared bat (Corynorhinus townsendii tion are concentrated on protecting caves ingens) are of particular interest in Okla- and the various types of bat colonies that homa. Each is federally listed as endangered they house (7). Most often these protection by the U.S. Fish and Wildlife Service. The measures are intended to eliminate distur- gray bat and the Ozark big-eared bat are both bance resulting from human entry into caves. obligate, year-round cave-dwelling bats. Protection is typically accomplished by con- The Indiana bat hibernates in caves in win- struction of gates at cave entrances, fencing ter and disperses during non-hibernating of cave entrances, placing warning signs at months to form roosts under bark and in tree entrances, and maintaining a close and posi- cavities in hardwood forests (4-6). tive rapport with private landowners. Pro- Persistent or casual human disturbance tection for cave-dwelling bat populations by at maternity caves and hibernacula contin- placing gates in the entrances of caves can ues to be implicated as a cause for the de- be an effective, immediate, and long-term cline in population of most cave-dwelling method to deter human access to critical bat bats (7-10). Disturbance at these caves may roosts. Proc. Okla. Acad. Sci. 80:133-137(2000) 134 K.W. MARTIN, W.L. PUCKETTE, S.L. HENSLEY, and D.M. LESLIE, JR.

CAVE GATING IN OKLAHOMA bats are similarly protected. Additionally, four caves that contain populations of Ozark Construction of restrictive structures such as blind cavefish (Amblyopsis rosae) and Ozark gates at cave entrances has evolved consid- blind crayfish (Cambarus sp.) are protected erably over the past 25 years. Original de- from human entry and vandalism by inter- signs were constructed in cage-like fashion nal gates. exterior to the cave entrance. This placement Population estimates for endangered resulted in the abandonment of some caves species of bats in eastern Oklahoma caves by bats (10,14,15). In Ottawa County, Okla- were initiated in 1981. Estimates for gray homa, such a gate was placed over a cave bat populations were conducted in 1983, entrance and resulted in eventual abandon- 1989, and 1999. Estimates for Ozark big- ment of the cave by a maternity colony of eared bat populations were conducted on an gray bats. annual basis beginning in 1986. Populations In 1980 and 1982, two additional caves of Ozark big-eared bats protected by inter- inhabited by maternity colonies of gray bats nal gates in Oklahoma caves are sporadic in Adair and Delaware Counties, Oklahoma and tend to fluctuate in size. Those caves were gated. The exterior features of these that are protected with gates house clusters cave entrances, however, caused the place- of 2-40 bats. The lone Indiana bat cave that ment of gates within dark zones of the cave is protected contains <15 bats at each moni- passages, 9 m and 15 m respectively, inside toring period (18). Colonies that are pro- the entrance. Each cave continues to be used tected with internal gates are located in by maternity populations of gray bats, esti- Adair, Delaware, Cherokee, Leflore, and mated at 9,000 and 12,500 bats, respectively, Ottawa counties of eastern Oklahoma. in 1999. These were the first instances of The gray bat is the only cave-dwelling cave-dwelling populations of bats protected species in eastern Oklahoma that roosts in by an “interior” gate system in the United large colonies, producing substantial guano States. A third gray bat maternity cave in accumulations on cave floors conducive to Cherokee County, Oklahoma, was gated by measurement for population analysis. His- using the same type of placement with simi- torically, roost sites in caves are located in lar results in 1991 (16). The external cage the same location from year to year. There protecting the original gray bat maternity are six maternity colonies of gray bats in east- colony in 1971, which was subsequently ern Oklahoma (16,19); four of these colonies abandoned, was reconstructed in 1997. An are protected from human disturbance by in- internal gate was placed 15 m inside the cave ternal gates. A fifth colony protected with passage, and the external cage was recon- an internal gate system is a non-maternity structed to be left open during periods of bat colony consisting of males and non-repro- use. A maternity colony of gray bats used ductive females. Population estimates con- the cave during maternity seasons in 1998 ducted at each of these caves prior to install- and 1999. Population estimates placed the ing gates in 1981, and post-installation esti- colony at 25,000 bats in 1998 and 27,000 in mates in 1999, suggest that colonies of gray 1999. Although general designs of gate con- bats continue to use each cave (Fig. 1). Stan- struction continue to evolve (17), placement dard methods of guano measurement in- of gates within dark zones of a cave pas- tended to estimate colonial gray bat popu- sages, such as these in eastern Oklahoma, is lations were established by Tuttle (12) and now an accepted protocol for cave gating Harvey, et al. (20). Maternity colonies were throughout the United States. distinguished by trapping lactating females Twenty-two entrances to caves in east- after parturation or by noting carcasses of ern Oklahoma are presently protected with dead young near roost sites inside cave pas- the use of internal gate designs. Five of these sages. caves are inhabited by colonies of gray bats. Each of the 22 caves that have been gated Twelve caves inhabited by Ozark big-eared in Oklahoma have unique physical charac- bats, and a single hibernaculum of Indiana teristics regarding passage size, location of

Proc. Okla. Acad. Sci. 80:133-137(2000) CAVE-GATING PROTECTING BAT POPULATIONS 135 the nearest bat roost to the entrance, and apparent acceptance of full passage gates by number of entrances used by bats. Internal resident bat populations in eastern Okla- gates are placed in such a manner as to pro- homa. tect the nearest historical roost area to the cave entrance. Gate distances from cave en- INHERENT EFFECTS OF CAVE GATING trances range from 3-17 m. Passage area where gates are located range from 1.38 m2 Since the mid-1980s, internal gate construc- – 9.5 m2. In contrast to some gates protect- tion has been of horizontal angle iron bars. ing gray bat colonies in the southeastern This material and design seems to maximize United States that do not completely fill the protection from human entry, have nominal cave passage, all internal gates in Oklahoma effects on airflow, and present limited ob- caves completely fill cave passages. Further- struction to bat flight (17). With the excep- more, one of the gray bat caves that is gated tion of a single cave that was gated before in Oklahoma has two entrances that are used angle iron gates became popular, all gates in during entrance and exit by bats. In this Oklahoma caves are of the angle iron design. particular cave, both of the entrances are Although placement of gates within protected with complete gates. Relatively “dark zones” of cave passages may be the small colony sizes (<30,000), relatively small most effective method to deter human ac- gated passages, and internal positioning of cess to critical bat roosts, their effects on resi- grill structures probably contribute to the dent bats and microclimate of cave interiors

27,500 —

25,000 — 1234 1234

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1234 1981 Estimates 22,500 — 1999 Estimates 20,000 —

17,500 —

15,000 —

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Number of Bats 12,500 — 1234 1234

1234 1234

1234 1234 1234

10,000 — 1234 1234 1234

1234 1234 1234

1234 123 123 1234 1234

7,500 — 1234 123 123 1234 1234

1234 123 123 1234 1234

1234 123 123 1234 1234 5,000 — 1234 123 123 1234 1234 1234 123 123 1234 1234

1234 123 123 1234 1234

1234 123 123 1234 1234 OK-92 OK-8 OK-9 OK-91 OK-1

Cave Identification

Figure 1. Population estimates of gray bats at five caves before and after they were protected by internal gate/grill systems in Oklahoma. Pre-gating estimates (1981 estimates) are from Grigsby and Puckett (19). Cave OK-1 is inhabited by a bachelor colony. The remaining caves are inhabited by maternity colonies.

Proc. Okla. Acad. Sci. 80:133-137(2000) 136 K.W. MARTIN, W.L. PUCKETTE, S.L. HENSLEY, and D.M. LESLIE, JR. have not been measured completely (14,21- in large caverns requiring expensive and 23). Various designs of gate construction and elaborate gate designs. These challenges and resulting effects on bat flight have been the inherent effects of internal gates on bat tested (17). However, effects that gates have populations may be precluded if population on the microclimate of cave interiors has not. monitoring at these caves indicate persistent It is suspected that cave gates alter airflow declines or abandonment because of human in cave passages (21,22,24). Altered airflow, disturbance. in turn, may affect ambient temperature, humidity, and substrate temperature. Roost ACKNOWLEDGMENTS substrate temperatures influence body temperature and ultimately metabolic rates of Many individuals, private landowners, and orga- hibernating bats (21,25). Fetal and neonatal nizations have provided assistance in gathering growth rates are affected directly by sub-op- data, constructing gates and have contributed time, timal temperatures of pregnant females and resources, and efforts to protecting the endemic bat juveniles. Poor thermoregulation in these species of Oklahoma. In particular we would like bats may result in slow maturation, thus re- to thank the Tulsa Regional Grotto of the National ducing survival and natality (26,27). Also it Speleological Society and the Tulsa Nature Con- is suspected that cave gates interrupt or im- servancy. Financial support was provided by Fed- pede the exit of large colonies of bats from eral Aid, Cooperative Endangered Species Conser- roost caves. An increase in swarming activ- vation under Project E-9 and E-22 of the Oklahoma ity before exiting or entering a cave that is Department of Wildlife Conservation, Rogers State gated may increase the risk of predation University, and the Oklahoma Cooperative Fish (10,14,17). and Wildlife Research Unit (Oklahoma State Uni- An unenviable dilemma still faces cave versity, U.S.G.S. Biological Resources Division, biologists and managers in protecting de- Oklahoma Department of Wildlife Conservation, clining populations of cave-dwelling species and Wildlife Management Institute, cooperating). of bats. The benefits of gating caves, and ultimately altering internal ambient cave REFERENCES conditions and bat flight, are weighed against persistent human entry and distur- 1. Harvey MJ, Altenbach JS, Best TL. Bats bance to critical bat roosts. Five of the six of the United States. Little Rock (AR): known maternity colonies of gray bats in Arkansas Game and Fish Commission Oklahoma are protected by internal gate 1999. 64 p. systems. The remaining maternity colony 2. McCracken GF. Cave conservation: has experienced human entry and distur- special problems of bats. National Spe- bance during each of the past two maternity leological Soc Bull 1989;51:49-51. seasons. Although 12 Ozark big-eared bat 3. Pierson, ED. Tall trees, deep holes, and caves are protected, they are typically pro- scarred landscapes: conservation biol- tecting small groups of bats, and none are ogy of North American bats. In: Kunz maternity caves. One maternity colony is TH, Racey P, editors. Bat biology and relatively obscure, and human disturbance conservation. Washington, D.C.: appears to be non-existent. The largest hi- Smithsonian Institution Press: 1999. p bernating population contains between 225- 309-325. 325 individuals annually. This colony, and 4. Humphrey SR, Richter AR, Cope JB. the remaining maternity colonies are more Summer habitat and ecology of the en- conspicuous and are susceptible to human dangered Indiana Bat, Myotis sodalis. J disturbance. Cave biologists have been re- Mammal 1977;58:334-346. luctant to construct internal gates in these 5. Kurta A, King D, Teramino JA, Stribley remaining caves inhabited by gray bat and JM, Williams KJ. Summer roosts of the Ozark big-eared bat populations. In each in- endangered Indiana bat (Myotis sodalis) stance, roost areas are either located in close on the northern edge of its range. Am proximity to the cave entrance or are located Mid Nat 1993;129:132-138. 6. Laval RK, Laval ML. Ecological stud- Proc. Okla. Acad. Sci. 80:133-137(2000) CAVE-GATING PROTECTING BAT POPULATIONS 137

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Proc. Okla. Acad. Sci. 80:133-137(2000)