Evidence-based bat conservation measures: example 4

Bat conservation in Bomboly Mine Lower Tunnel, Hungary

Type of example:

Best practice case / positive example of bat conservation

Name of the underground site:

Bomboly Alsó-táró / Bomboly Mine Lower Tunnel

Site location:

Hungary, Borsod-Abaúj Zemplén County, Mád, Mádi Bomboly-bánya

Type of underground site:

Mine

The site is used by bats:

In winter / for hibernation

Legal protection of the site:

Legally protected

Brief description of the legal protection status of the site:

Natura 2000 site (HUAN21008), protected under the Habitats Directive. Protected artificial subterranean cavity at national level.

Conservation measure implemented:

1. Gate

2. Stabilization of mine tunnels

Year(s) or exact date(s) of implementing conservation measure:

2010 and 2018

Bat species targeted by the conservation measures:

Rhinolophus ferrumequinum, Rhinolophus hipposideros, Myotis myotis, Myotis blythii, Myotis emarginatus, Myotis dasycneme, Plecotus austriacus

Details of the conservation measures:

The main objective was to create a safe bat roost on the site of a collapse-prone, disturbed mineshaft. As a first step the old wooden made entrance and the beginning section was rebuilt with a new concrete stone wall over a length of 10 meters. The debris from the collapsed sections were cleared from the inner parts of the tunnel, and these parts also have been rebuilt. The other internal sections, which were at risk of collapsing, have been reinforced with concrete. As an entrance, an extra strong, galvanized door with a special lock was installed. On the upper part of this door, a 20x100 cm large entrance was created for the bats.

The situation before implementing the conservation measures:

The total length of the shaft is about 350 m, the width is 1.3-1.8 m and the average height is 1.6-1.8 m. After the end of mining activities in 1979, as an entrance a 2.0 m deep vertical shaft covered with planks was left behind; this overtime became almost fully covered with debris. The cover was illegally broken in 2005, allowing small numbers of bats to hibernate in the shaft. By 2009, the tunnel had reached a life-threatening condition, with a section of about 20 meters partially collapsed. Very few bats were using the tunnel system before the bat protection intervention started. Before starting the physical works, Aggtelek NPD first entered into a long-term cooperation agreement with the owners of the land concerned.

The situation after implementing the conservation measures:

Bats appeared in greater numbers after the intervention and their numbers have been increasing ever since. Over the past 10 years, the tunnel has become a very species-rich hibernation site, with 13 species recorded so far. The large population of the great horseshoe bat (Rhinolophus ferrumequinum) is particularly valuable, but other important species (e.g. Myotis dasycneme, M. bechsteinii, M. emarginatus) are also regularly found here. During construction, we have not experienced any bat mortality or damage at all. The bat population in the mine shaft is usually surveyed twice a year, in February and May/June. We also carry out continuous microclimate monitoring in the tunnel system.

Challenges encountered during implementation:

As there was a very important summer bat roost nearby, we did not want to time the work during the maternity season. As the survey data showed that only a few individuals had previously used this winter roost, we timed the works for the winter period. To ensure that the bats in this tunnel would not hibernate, the works started in September 2010. The works were completed in March 2011. Winter work (especially construction) was not easy.

Challenges encountered after implementation:

A few years later, heavy rains caused a landslide at the front door and damaged a short interior section. For this reason, in 2018, a large retaining wall had to be built at the entrance to prevent damage, and the collapsed mine section had to be stabilized.

Details about citation:

Boldogh S., Gruber P., Kis Herczegh P., Berczik P., Szabó M., Bihari Z. (2012): Conservation actions in subterranean bat habitats within the operational territory of the Aggtelek National Park Directorate. Speleobats Int. Conference, 2012. Miskolc, Hungary. (poster)

Attached media:

The entrance before the renovation, photographed from above (2008).

Demolition of the original entrance and construction of an extended new access tunnel (2011).

Internal section in need of reconstruction (2010).

The rebuilt new entrance reinforced with a retaining wall (2018).

Dimensions of the entrance door, in mm (“Denevérnyílás” = opening for bats).

Sharing experiences (2012).

Number of wintering bats in the Bomboly mine (the red arrow indicates the date of the conservation intervention).

Example provided by:

Sándor A., Boldogh, Aggtelek National Park Directorate¹, BirdLife Hungary Mammal Conservation Group², Hungary