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What Works in Conservation 2021

 | 
William Junior Sutherland
, 
Lynn V. Dicks
, 
Silviu O. Petrovan
, 
et al.

2. Bat conservation

2.6 Threat: Human intrusions and disturbance

Texte intégral

2.6.1 Caving and tourism

Likely to be beneficial

Impose restrictions on cave visits

1Four studies evaluated the effects of imposing restrictions on cave visits on bat populations. One study was in each of the USA, Canada, Madagascar, and Turkey.

2COMMUNITY RESPONSE (0 STUDIES)

3POPULATION RESPONSE (2 STUDIES)

4Abundance (2 studies): Two before-and-after studies in Canada and Turkey found that bat populations within caves increased after restrictions on cave visitors were imposed.

5BEHAVIOUR (2 STUDIES)

6Behaviour change (2 studies): One study in the USA found that reducing the number of people within cave tour groups did not have a significant effect on the number of take-offs, landings or overall activity (bat movements) of a cave myotis colony roosting within the cave. One study in Madagascar found that increasing visitor approach distances, along with avoiding direct illumination of bats, reduced the alertness and number of take-offs of Madagascan rousettes during experimental cave tours.

7Assessment: likely to be beneficial (effectiveness 67 %; certainty 50 %; harms 0 %).

https://www.conservationevidence.com/​actions/​1002

Trade-off between benefit and harms

Install and maintain cave gates to restrict public access

8Eleven studies evaluated the effects of installing cave gates on bat populations. Six studies were in the USA and five studies were in Europe.

9COMMUNITY RESPONSE (0 STUDIES)

10POPULATION RESPONSE (7 STUDIES)

11Abundance (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.

12Condition (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.

13BEHAVIOUR (5 STUDIES)

14Use (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.

15Behaviour 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 USA found that significantly fewer bats emerged from a cave with a gate installed compared with a cave with a fence. Assessment: trade-off between benefit and harms (effectiveness 70 %; certainty 50 %; harms 20 %).

https://www.conservationevidence.com/​actions/​999

Unknown effectiveness

Install fencing around cave entrances to restrict public access

16Two studies evaluated the effects of installing fencing around cave entrances on bat populations. One study was in the USA and one study was in Spain. COMMUNITY RESPONSE (0 STUDIES)

17POPULATION RESPONSE (1 STUDY)

18Abundance (1 study): One replicated, site comparison study in Spain found no difference in the population growth rates of bats roosting in caves with and without fencing or gates installed.

19BEHAVIOUR (2 STUDIES)

20Use (1 study): One replicated, site comparison study in Spain found no difference in the occupancy rates of bats roosting in caves with and without fencing or gates installed.

21Behaviour change (1 study): One controlled, before-and-after study in the USA found that significantly more southeastern myotis bats and gray myotis bats emerged from a cave after a steel gate was replaced with a fence.

22Assessment: unknown effectiveness (effectiveness 40 %; certainty 20 %; harms 0 %).

https://www.conservationevidence.com/​actions/​1991

Minimize noise levels within caves

23One study evaluated the effects of minimizing noise levels within caves on bat populations. The study was in the USA.

24COMMUNITY RESPONSE (0 STUDIES)

25POPULATION RESPONSE (0 STUDIES)

26BEHAVIOUR (1 STUDY)

27Behaviour change (1 study): One controlled study in the USA found that experimental cave tours with groups that did not talk resulted in fewer bat flights than when groups did talk, but talking did not have an effect on the number of bat movements.

28Assessment: unknown effectiveness (effectiveness 40 %; certainty 21 %; harms 0 %).

https://www.conservationevidence.com/​actions/​1995

Restrict artificial lighting in caves and around cave entrances

29One study evaluated the effects of restricting artificial lighting in caves on bat populations. The study was in the USA.

30COMMUNITY RESPONSE (0 STUDIES)

31POPULATION RESPONSE (0 STUDIES)

32BEHAVIOUR (1 STUDY)

33Behaviour change (1 study): One controlled study in the USA found that using low intensity white lights or red lights in caves resulted in fewer bat flights than with full white lighting, but the number of bat movements was similar between all three light treatments.

34Assessment: unknown effectiveness (effectiveness 15 %; certainty 12 %; harms 0 %).

https://www.conservationevidence.com/​actions/​1994

No evidence found (no assessment)

35We have captured no evidence for the following interventions:

  • Inform the public of ways to reduce disturbance to bats in caves

  • Introduce guidelines for sustainable cave development and use

  • Minimize alterations to caves for tourism

  • Provide artificial subterranean bat roosts to replace roosts in disturbed caves

  • Restore and maintain microclimate in modified caves

  • Retain bat access points to caves

  • Train tourist guides to minimize disturbance and promote bat conservation.

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