Action: Install and maintain cave gates to restrict public access
- Eleven studies evaluated the effects of installing cave gates on bat populations. Six studies were in the USA and five studies were in Europe.
COMMUNITY RESPONSE (0 STUDIES)
POPULATION RESPONSE (7 STUDIES)
- Abundance (7 studies): Three of four before-and-after studies (including one replicated study and one controlled study) in the Netherlands, the USA, Spain and Turkey found more or similar numbers of bats in caves and a bunker after gates were installed to restrict public access. The other study found fewer bats in caves after gates were installed. Two before-and-after studies in the USA and Spain found more bats within two caves after the size of the gated entrances were increased. One replicated, before-and-after study in the USA found that installing cave gates resulted in population increases or decreased rates of decline for 13 of 20 colonies of Indiana bat. One replicated, site comparison study in Spain found no difference in the population growth rates of bats roosting in caves with and without cave gates.
- Condition (1 study): One site comparison study in the USA found that bats hibernating in a cave with a wall and gate over the entrance lost more body mass than bats in a nearby unmodified cave.
USAGE (5 STUDIES)
- Use (1 study): One replicated, site comparison study in Spain found no difference in the occupancy rates of bats roosting in caves with and without cave gates.
- Behaviour change (4 studies): One replicated, controlled, before-and-after and site comparison study in the USA found that bats at cave entrances circled more and entered caves less after gates were installed. One replicated study in the USA found that bats flew through gates with a funnel design more frequently than gates with a round bar or angle iron design. One randomized, controlled, before-and-after study in the UK found that fewer bats flew through cave gates when the spacing between horizontal bars was reduced. One before-and-after study in the USA4 found that significantly fewer bats emerged from a cave with a gate installed compared with a cave with a fence.
Recreational users of caves can disturb both nursing and hibernating colonies of bats causing abandonment of young or arousal from hibernation. Gates have been installed at cave entrances to restrict public access and reduce human disturbance. However, cave gating can also impede access by bats and early installation attempts from the 1950s to the 1970s often resulted in roost abandonment (Tuttle 1977). For evidence relating to gates at mines, see ‘Threat: Energy production and mining – Mining – Install and maintain gates at mine entrances to restrict public access’.
Tuttle M.D. (1977) Gating as a means of protecting cave dwelling bats. Pages 77–82 in: T. Aley & D. Rhodes (eds.) 1976 National Cave Management Symposium Proceedings, Speleobooks, Albuquerque, USA.
Supporting evidence from individual studies
A before-and-after and site comparison study in 1976–1991 in two caves in Indiana, USA (Richter et al 1993) found that Indiana bats Myotis sodalis hibernating within a cave modified with a stone wall and gate constructed at the entrance entered hibernation at a 5% higher body mass and lost 42% more body mass than bats in an unmodified cave 4 km away. The stone wall and gate in the modified cave restricted the cave opening by 62% reducing airflow and resulting in average winter temperatures 5°C higher than in the unmodified cave. In 1977, the stone wall was removed and replaced with steel bars. From 1977 to 1991, the population of Indiana bats in the cave increased from 2,000 to 13,000 bats. In each of two caves, temperatures were measured near to hibernation sites every other week, and bats were counted and weighed in early winter (October–November 1976) and late winter (March 1977). Bats were monitored with a biannual census from 1977 to 1991 (no other details reported).
A controlled, before-and-after and site comparison study in 1976–1984 in four abandoned underground war bunkers in the Netherlands (Voûte & Lina 1986) found that the number of hibernating bats at three bunkers increased after human access had been restricted by installing grilles or sealing entrances, and the number of bats in one unmodified bunker remained constant. The number of hibernating bats in three bunkers increased over one and a half years after grilles were installed or entrances were sealed (before: 15–35 bats; after: 30–115 bats). Bunker entrances were either sealed completely or grilles of vertical bars were installed in 1977 or 1980. Sand and debris were also removed from one of the bunkers. The individual effects of each intervention are not reported. Bat numbers at a fourth bunker with no restrictions in place remained constant (1976: 12 bats; 1984: 13 bats). At each of four bunkers, annual winter counts were conducted from 1976 or 1978 until 1984.
A small replicated study in 1985 at two caves in Alabama and West Virginia, USA (White & Seginak 1987) found that Townsend’s big-eared bats Plecotus townsendii and gray myotis bats Myotis grisescens flew more frequently through test frames at gated cave entrances with a round bar design or angle iron design than a funnel design. A greater proportion of Townsend’s big-eared bats and gray myotis bats flew through test frames with a round bar design (average 40% of big-eared bats and 20% of gray myotis bats exiting through the cave entrance), or angle iron design (21% of big-eared bats and 16% of gray myotis) than a funnel design (7% of big-eared bats, 2% of gray myotis). At one entrance at each of two caves, a 1 m2 test frame was installed in front of an existing gate with a round bar design. Inserts of three different designs were installed in the frames: round bar (19 mm round steel bars in a 615 x 154 mm pattern), angle iron (103 mm angle iron welded 154 mm apart in a horizontal pattern) and funnel (a 1 m2 one-way metal funnel narrowing to an exit hole of 230 x 230 mm). Each of three designs was tested for a total of 25 nights/cave in May–August 1985. At dusk, bats were counted emerging through the frame and the remainder of the cave entrance.
A before-and-after study in 1994–1996 at one cave on a forested limestone ridge in north Florida, USA (Ludlow & Gore 2000) found that a steel bar gate across the cave entrance resulted in fewer southeastern myotis bats Myotis austroriparius and gray myotis bats Myotis grisescens emerging than when the gate was replaced with a fence. Fewer bats emerged from the cave entrance when it had a steel bar gate across it (average 306 bats/month, 8% of total bats emerging from cave) than when the gate was replaced with a fence (average 1,517 bats/month, 48% of total bats emerging). The number of bats emerging from a second un-gated entrance to the cave decreased after the gate was replaced with a fence (from 3,609 to 1,651 bats/month). The cave gate consisted of steel bars 13 mm in diameter spaced 100 mm apart in one direction and 465 mm in the other. Before removal of the gate a 2.2 m high chain-link fence was erected 6–8 m from the cave entrance. Emerging bats were counted monthly at the open entrance and gated entrance for one year before and one year after the cave gate was removed (August 1994 to July 1996).
A replicated, before-and-after study in 1981–2001 at five caves in a limestone plateau in northeastern Oklahoma, USA (Martin et al 2003) found that after cave gates were installed the number of gray myotis bats Myotis grisescens increased at two caves and remained similar at three caves. After cave gates were installed, the number of gray myotis bats was estimated to increase at two caves (before: 3,031–15,047 bats; after: 12,500–32,136 bats) and remain similar at three caves (before: 3,693–18,031 bats; after: 3,721–9,533 bats). At each of six caves, gates were installed (horizontal angle-iron bars and 150 mm spacing) in different years between 1981 and 2000. Numbers of gray myotis bats in each of six caves were estimated during the summers of 1981–1983, 1991, 1999 and 2001 from the size of guano accumulation.
A replicated, controlled, before-and-after and site comparison study in 2003 at 28 cave and mine sites between Ontario, Canada and Tennessee, USA (Spanjer & Fenton 2005) found that at cave and mine entrances with gates, bats circled, retreated more and passed through less often than at ungated entrances. Bats circled and retreated significantly more and passed through less at entrances with existing cave gates (37% of bats circled and retreated, 50% passed through) or newly installed mock gates (60% circled and retreated, 25% passed through) than at ungated entrances (23% circled and retreated, 68% passed through). Separate results for caves and mines are not provided. Seven caves or mines had existing gates (of various designs), twelve caves or mines were ungated and had mock wooden gates installed (horizontal bars 25 mm diameter with 146 mm spacing). Ungated entrances were surveyed before and after mock gates were installed. At each of 28 sites, observations of behaviour were made during 3–4 x 5 minute periods during 1–2 nights in July–October 2003.
A randomized, controlled, before-and-after study in 2004 at a cave in a wooded limestone valley in northern England, UK (Pugh & Altringham 2005) found that cave gates with horizontal bar spacings of 130 mm and 100 mm caused significantly more bats to abort attempts to enter the cave through the gate, but gates with spacings of 150 mm had no effect on bat behaviour. The proportion of bats entering the cave decreased after gates were installed with horizontal spacings of 130 mm (without gate: 0.20–0.28 bats/30 min; with gate: 0.07 bats/30 min) and 100 mm (without gate: 0.20 bats/30 min; with gate: 0.08 bats/30 min). Gates with horizontal spacings of 150 mm had no significant effect (without gate: 0.14–0.16 bats/30 min; with gate: 0.10 bats/30 min). Bat behaviour was similar before the gates were installed and after they were removed. One cave entrance was used for the experiments (1.5 m diameter) with custom made gates (made with 15 mm diameter plastic tubing) of each of three horizontal spacings (100, 130 and 150 mm) positioned over it. Bats were recorded for 3 x 30 minute periods with the gate open (‘before’), closed, and open again (‘after’). The behaviour of swarming bats (mostly Natterer’s bats Myotis nattereri) was observed on 6–10 nights for each of three gate designs using night video recording, with gate size randomized between nights.
A before-and-after study in 1998–2009 and 2010 in one cave in Castile and León, Spain (Alcalde et al 2012) found fewer bent-wing bats Miniopterus schreibersii using a cave after the installation of a cave gate with a narrow entrance. Between six and nine years after the installation of a cave gate with a narrow entrance, fewer bent-wing bats were counted using the cave than before the installation of the gate (before: 600–700 bats; after: 200–280 bats), but statistical tests were not carried out. However, >450 bent-wing bats were counted seven months after the gated opening was enlarged. In 2001, a cave gate covering 75% of the cave entrance was fitted to a small cave. In March 2010, the cave gate opening was enlarged from 3.5 x 1 m to 7 x 2 m. Bats were counted approximately once/month in 2010 using infrared lights. Data were compared to previously published bat counts at the cave from 1998–2009.
A before-and-after study in 2002–2008 at a cave system in forested mountains of Turkey (Paksuz & Özkan 2012) found that installing cave gates, along with other restrictions to reduce human disturbance, resulted in an increase in the number of 15 bat species using two caves in the system. Maximum counts of bats in the two caves were higher after the cave system was opened to tourism and cave gates and other restrictions were put in place (before: 42,800 hibernating and 7,900 breeding bats; after: 54,600 hibernating and 11,000 breeding bats). The study does not distinguish between the effects of cave gating and other interventions carried out at the same time. A third cave in the system, which remained ungated and closed to tourism, had similar numbers of bats throughout the study period. Before opening to tourism, recreational users had made frequent uncontrolled visits to the caves. After opening for tourism in 2003, gates were installed on two cave entrances (horizontal iron bars with 200 mm spacing), daily and seasonal timing of tourist visits were controlled, information signs were erected, and lights were switched off outside of visiting times. Bat colonies were counted every 40 days with 15 surveys before (2002–2004) and 38 surveys after opening to tourism (2004–2008). Update 2018: The findings of this study have been challenged, see Furman et al. 2012.
Furman A., Çoraman E. & Bilgin R. (2012) Bats and tourism: a response to Paksuz & Özkan. Oryx, 46, 330–330.
A replicated, before-and-after study in 1979–2009 of 20 caves in the USA (Crimmins et al 2014) found that installing cave gates resulted in population increases or decreased rates of decline for 13 of 20 colonies of Indiana bat Myotis sodalis. Thirteen of the populations were declining before cave gates were installed, and either increased (8 populations) or continued to decline at a reduced rate (5 populations) after installation (data reported as results of statistical models). Seven of the populations were increasing before cave gates were installed, and either declined (4 populations) or continued to increase at a reduced rate (3 populations) after installation (data reported as results of statistical models). Annual population counts were carried out between 1979 and 2009 using a standard protocol before (during 4–15 years) and after (during 4–16 years) installation of cave gates. All caves had average populations of >100 individuals. Change-point detection modelling was used to estimate population trends. The authors state that confounding factors, such as gate design, human activities and regional differences are not accounted for.
A replicated, site comparison study in 1997–2014 of 34 caves in eastern Spain (Machado et al 2017) found that installing cave gates or fencing did not affect the occupancy or population growth rates of nine bat species. Average occupancy rates were similar in caves with (11 of 20, 57% of caves occupied) and without (8 of 14, 60% of caves occupied) gates or fencing (separate results for cave gates and fencing not reported). Population growth rates also did not differ significantly between caves with or without gates or fencing (data reported as results of statistical models). Fourteen caves had fencing installed (2.5 m high gridded metal fences in a 20 m radius around the cave entrance), two caves had rigid panels installed (filling three-quarters of the cave entrance), two caves had iron bars installed (filling the entire cave entrance), and two caves had cave gates installed (with 2 x 1 m2 openings for bats). Fourteen caves did not have gates or fencing installed. Bats were counted annually using infrared video cameras and bat detectors at cave entrances between May and July in 1997–2014.
- Richter A.R., Humphrey S.R., Cope J.B. & Brack V. (1993) Modified cave entrances: thermal effect on body mass and resulting decline of endangered indiana bats (Myotis sodalis). Conservation Biology, 7, 407-415
- Voûte A.M. & Lina P.H.C. (1986) Management effects on bat hibernacula in the Netherlands. Biological Conservation, 38, 163-177
- White D.H. & Seginak J.T. (1987) Cave gate designs for use in protecting endangered bats. Wildlife Society Bulletin, 15, 445-449
- Ludlow M.E. & Gore J.A. (2000) Effects of a cave gate on emergence patterns of colonial bats. Wildlife Society Bulletin, 28, 191-196
- Martin K.W., Leslie D.M., Payton M.E., Puckette W.L. & Hensley S.L. (2003) Internal cave gating for protection of colonies of the endangered gray bat (Myotis grisescens). Acta Chiropterologica, 5, 143-150
- Spanjer G.R. & Fenton M.B. (2005) Behavioral responses of bats to gates at caves and mines. Wildlife Society Bulletin, 33, 1101-1112
- Pugh M. & Altringham J.D. (2005) The effect of gates on cave entry by swarming bats. Acta Chiropterologica, 7, 293-299
- Alcalde J.T, Artácoz A. & Meijide F. (2012) Recovery of a colony of Miniopterus schreibersii from a cave, Cueva de Ágreda, in Soria. Barbastella, 5, 32-35
- Paksuz S. & Özkan B. (2012) The protection of the bat community in the Dupnisa Cave System, Turkey, following opening for tourism. Oryx, 46, 130-136
- Crimmins S.M., McKann P.C., Szymanski J.A. & Thogmartin W.E. (2014) Effects of cave gating on population trends at individual hibernacula of the Indiana bat (Myotis sodalis). Acta Chiropterologica, 16, 129-137
- Machado M.C., Monsalve M.A., Castello A., Almenar D., Alcocer A. & Monros J.S. (2017) Population trends of cave-dwelling bats in the Eastern Iberian Peninsula and the effect of protecting their roosts. Acta Chiropterologica, 19, 107-118