Action: Install and maintain gates at mine entrances to restrict public access
- Four studies evaluated the effects of installing gates at mine entrances on bat populations. Three studies were in the USA and one in Australia.
COMMUNITY RESPONSE (1 STUDY)
- Richness/diversity (1 study): One replicated, before-and-after study in the USA found that significantly fewer bat species entered mines after gates were installed.
POPULATION RESPONSE (1 STUDY)
- Abundance (1 study): One replicated, controlled, before-and-after study in Australia found fewer bats in mines after gates were installed.
USAGE (3 STUDIES)
- Use (1 study): One before-and-after study in the USA found that 43 of 47 mines continued to be used 12 years after gates were installed, however bats abandoned four mines with ‘ladder’ design gates.
- Behaviour change (2 studies): Two replicated, before-and-after or site comparison studies in the USA and Australia found that bats at mine entrances circled more and entered mines less after gates were installed.
Gates may be installed at mine entrances to restrict public access and reduce human disturbance. However, gates 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 cave gates, see ‘Threat: Human intrusions and disturbance – Caving and tourism – Install and maintain cave gates 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 replicated, controlled, before-and-after and site comparison study in 2003 at 28 mine and cave sites between Ontario, Canada and Tennessee, USA (Spanjer 2006) found that at mine and cave 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 mine or 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 mines and caves are not provided. Seven mines or caves had existing gates (of various designs), twelve mines or caves 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 replicated, controlled, before-and-after study in 2003 at four derelict mines in a forested area of south-eastern Australia (Slade & Law 2008) found that installing gates with 125 mm horizontal spacing resulted in fewer eastern horseshoe bats Rhinolophus megaphyllus and Schreiber’s bats Miniopterus schreibersii using the mines and more bats aborted exit and entry flights, whereas gates with horizontal spacings of 450 mm and 300 mm did not affect bat numbers or behaviour. Fewer bats used two mines after gates with a 125 mm horizontal spacing were installed (before: 120 and 540 bats; after: 30 and 290 bats). The number of bats aborting exit and entry flights also significantly increased (data reported as standardized results). Gates with horizontal spacings of 450 mm and 300 mm did not significantly affect bat numbers or behaviour. Bat numbers at two similar control mines either remained constant or increased. Two mines were fitted with gates (made from 20 mm plastic tubing), and two were left ungated (controls). In March–April 2003, bat activity at the two experimental mines was observed in four stages of 11 days each: before gating followed by the successive addition of horizontal gate bars to reduce the spacing size (to 400, 300 and 125 mm). Bats were logged automatically using infra-red beams, and night-vision video cameras recorded flight behaviour for 30 minutes at dusk and dawn.
A before-and-after study in 1991–2004 at 47 gated abandoned mines in forested areas of Colorado, USA (Navo & Krabacher 2005) found that 43 of 47 mines with gates of various designs continued to be used by eight bat species up to 12 years after installation. None of 43 mines with full gates with or without culverts were abandoned by bats. Three mines with ladder gates and one mine with a culvert ladder gate were abandoned by bats. Four types of gate were evaluated, all with bar spacings of 150 mm. Traditional gates allowed access to bats across the whole gate, ladder gates allowed access to bats at the centre only, and both types of gate were also constructed in metal culverts where mine entrances were too unstable to anchor the gate itself. Each of 47 mines were surveyed 2–10 times in 1991–2004 using multiple methods (catching, visual counts and infra-red motion detectors).
A replicated, before-and-after study in 2002–2004 at five pairs of abandoned mines in northern Idaho, USA (Derusseau & Huntly 2012) found that installing gates resulted in fewer bats and fewer bat species entering the mines. Significantly fewer bats entered mines after gates were installed with an overall decrease of 65% across all gated mines (before: average 29 bat entries; after: 10 bat entries). The number of bats entering five ungated mines increased by 45% over the same period (‘before’: 20 bat entries; ‘after’ 32 bat entries). Significantly fewer bat species entered the mines after gates were installed (before: average 2.3 bat species; after: 1 bat species), but no change was observed at ungated mines (‘before’: 2 bat species; ‘after’: 1.8 bat species). Gates were installed at five of 10 mines in 2002 and 2003. Gates had vertical supports (10 x 10 x 1 cm iron) and horizontal bars (10 x 10 cm angle iron) with gaps of <14.6 cm. Each of five pairs of mines was surveyed twice in July–August in two consecutive years in 2002–2004 (before and after gating). One mist net survey and one video survey were carried out at the mine entrance of each site/year.
- Spanjer G.R. & Fenton M.B. (2005) Behavioral responses of bats to gates at caves and mines. Wildlife Society Bulletin, 33, 1101-1112
- Slade C.P. & Law B.S. (2008) An experimental test of gating derelict mines to conserve bat roost habitat in southeastern Australia. Acta Chiropterologica, 10, 367-376
- Navo K.W. & Krabacher P. (2005) The use of bat gates at abandoned mines in Colorado. Bat Research News, 46, 1-8
- Derusseau S.N. & Huntly N.J. (2012) Effects of gates on the nighttime use of mines by bats in northern Idaho. Northwestern Naturalist, 93, 60-66