Bat Bridge
Bat bridges are structural constructions over highly frequented traffic routes - such as highways or railway lines - that are intended to enable low-flying bats to cross safely. The bridges, which vary greatly in shape, are intended to serve as flight corridors for the bats, which they use ultrasound to orient themselves on when they fly over them.
Similar to green bridges, bat bridges connect animal habitats that have been cut up in order to counteract the consequences of open spaces being cut up by traffic routes. Public opinion about bat bridges is divided, as their use - also scientifically - is extremely controversial.
background
So far, 24 bat species from a total of nine genera and two families - all of them horseshoe bats or smooth noses - have been detected in Germany. Each of these species is one of the particularly and strictly protected species according to the Federal Nature Conservation Act and the Fauna-Flora-Habitat Directive since 1992. As such, their habitats, regardless of their location, must not be impaired or destroyed.
Legal guidelines
According to the intervention compensation regulation of German law, all avoidable interventions in the ecosystem are generally prohibited. According to the Federal Nature Conservation Act, such interventions are all "changes in the design or use of land areas [...] that can significantly impair the performance and functionality of the natural balance or the landscape". If such interventions cannot be avoided, they must be compensated for. All impairments of nature and landscape caused by the intervention must be functionally compensated. Avoidable impairments must be avoided. Compensatory and replacement measures are provided to avoid unavoidable impairments. Accordingly, the impaired functions of the ecosystem at the same location must be promptly improved by another measure or nature and landscape must be upgraded at another location.
As specially and strictly protected species, interventions in the habitats of bats require measures that go well beyond the usual compensation measures according to the intervention rules. The prohibition of impairing the habitats of bats according to the Habitats Directive makes structural measures - these are usually the construction of traffic routes, often long-distance roads - in the habitats of the animals much more difficult. If such structural interventions are nevertheless carried out, strict guidelines must be observed. The functions of the natural balance impaired by construction measures must be completely taken over at the same location by other measures. Proof of the success of such measures is mandatory before the construction work. The measures must be carried out before the start of construction. The structural measures are only to be started after the compensation measures are demonstrably effective. In contrast to the normal compensatory measures, the disturbances in the functions of nature and landscape not only have to be improved, but also completely compensated for.
activities
In the course of these guidelines, various measures are conceivable that are intended to reduce the consequences of open-field fragmentation for the bat habitats to a minimum. Various studies on several green bridges have shown that the construction of green bridges not only offers Edaphones the opportunity to connect the cut-up living space. Although they were not the main target species because of their ability to fly, rare bats also used bridges that were not aligned with existing flight corridors. The bridges were not only used by most species as an overflight aid, but also as a hunting area. Special bat bridges are supposed to achieve a similar effect. Some of these structures have been erected, especially in the United Kingdom, as the responsible authorities consider the bridges as protection for endangered bat species in the context of the Habitats Directive, which is also applicable here. It is hoped that the bridges will be used by the animals as a crossing aid.
Structure and designs
The various existing bat bridges vary greatly in shape. The aim of the constructions is to imitate natural plantings and growth such as shrubs or deciduous trees as exactly as possible during ultrasound location by bats, so that they accept the bridges as new guidelines. The different executions pursue strongly divergent concepts in order to realize this.
Many bridges consist of several parallel steel cables, which are anchored to vertical girders on both sides of the roadway and run a few meters above it. Partly spherical sound reflectors are mounted on the steel cables. They scatter the echo of the bats in all directions. Above all, they are supposed to simulate the leaves of hedges and bushes, which in turn reflect the sound in numerous directions due to their density and different orientations. A similar design consists of three close-meshed nets, which - attached to a mast on each side of the street - are stretched across the street. A net forms the underside and the other two are attached perpendicular to it so that a “U” shape is created in cross-section. The actual bridge body is only a few meters high and wide.
There are also types of construction that resemble a green bridge in their appearance. Instead of the masts, embankments are created next to the roadway, which serve as the base of the bridge. The bridge itself can, for example, consist of a short, solid steel beam. The embankments themselves can be planted to create the impression of a green bridge.
In addition, there are two bridges in Biberach an der Riß, which are made of solid metal and apparently resemble a conventional bridge - such as a pedestrian bridge.
List of crossing aids for bats (selection)
| country | Street | place | design type | costs | opening | swell |
|---|---|---|---|---|---|---|
| UK |  |
Workington (Cumbria) | underpass | ? | ? | |
| Cable bridge | ? | ? | ||||
 |
High Newton (Cumbria) | Two underpasses | ? | ? | ||
| Cable bridge | £ 45,000 | ? | ||||
 |
Dobwalls (Cornwall) | Bridge body made of nets | £ 300,000 | ? | ||
 |
Distington (Cumbria) | Cable bridge | £ 34,133 | ? | ||
 |
Haydon Bridge (Northumberland) | Cable bridge | £ 60,000 | ? | ||
 |
Pwllheli (Gwynedd, Wales) | ? | ? | |||
 |
Abergavenny (Monmouthshire, Wales) | ? | ? | |||
 |
Porthmadog (Gwynedd, Wales) | Steel girders between embankments | £ 650,000 | |||
| Penmaen? | Penmaen? | Wire nets | ? | |||
| DE |
|
Biberach an der Riss | Full metal bridge | € 400,000 | 2013 | |
| FR |  |
Roquefort (Landes) | Full metal bridge | € 500,000 | 2012 | |
 |
Balbigny | Full metal bridge | ? | 2012 |
functionality
Echolocation of bats
The functionality of bat bridges is based on the echolocation of bats. These generate locating sounds in the ultrasound range in the larynx. The nocturnal animals put together a three-dimensional image from the sound waves reflected from their surroundings. To do this, they generate calls whose sound waves are strongly bundled and thrown in a certain direction. The bats' funnel-shaped ears are extremely sensitive to both the direction and the sound quality of the echoes of the sound waves that are thrown back from objects in the vicinity or from prey and can be moved individually to locate certain sound sources more precisely. Both ears can perceive the animals independently of each other. When the echoes arrive, time differences in the arrival of the sound are evaluated so that an exact three-dimensional image of the environment can be made in the brain. Due to the differentiated analysis of the frequency and amplitude of the echoes, bats can determine the size, shape and surface structures and thus the material of the reflectors. Using the Doppler effect, it is also possible for them to identify the state of motion. Bats can modulate their calls in such a way that they can orientate themselves in complex environments and localize objects with an accuracy of a few millimeters.
orientation
With the help of ultrasound tracking, bats can orientate themselves perfectly even in complete darkness. Most species use linear structures in flight - especially hedges and forest edges - as guidelines. In addition, pronounced hedge landscapes allow the animals a larger area for foraging. In addition, these hedges also serve as a habitat for prey, especially insects. Bats often use the same routes over the years to get from their roost to their hunting grounds. "Structure-bound" species fly only a few meters above the ground, as these bats echolocation only reach a few hundred meters. Due to a low flight altitude, the animals can orientate themselves better to their guidelines. Studies have shown that the whiskered bat, for example, is only 0.3 to 1.7 meters and the water bat about 2.1 to 4.5 meters away from their lead structures. The maximum distances can only be found if the guidelines are disturbed.
In the course of the fragmentation of the landscape through traffic routes (roads, railway lines, etc.) or settlement areas, the habitat of numerous bat species is often severely restricted. So u. A. Hedge landscapes are destroyed and the functions of the hedges as a guide for bats are lost. Sleeping and hunting areas are separated from each other by the traffic routes, making it more difficult for the bats to forage. In addition, the habitat of the animals' prey is reduced, so that hunting is sometimes impaired. Due to the short range of echolocation, a few meters of interruption in the line biotopes are often enough to significantly disrupt the animals' navigation. Since these also fly very low, there is a risk of collision with traffic, which endangers the population of the animals and traffic safety.
Bat bridges are intended to reduce these drastic consequences of the fragmentation of open spaces by taking over the function of the interrupted or destroyed orientation lines. The bats, whose habitat is crossed by the traffic routes, should orient themselves on the bridges when they fly over them. The idea is that the ultrasonic echo of the bridges is similar to that of natural vegetation and that the animals orientate themselves to these when they fly over the traffic routes. Since the bridges run a few meters above them, the risk of collision should be avoided.
Use
Little details are known about the efficiency of the bat bridges. Since there are only a few such constructions. At almost all locations, no meaningful data that could have served as a reference for later investigations was collected before the construction of the traffic routes. Little is known about the original flight behavior of bats and their populations in the corresponding areas, so that comparative studies are often not possible. So far there have also been no studies on the “efficiency” of bat bridges. No data have been collected on how many bats actually use the crossing aids and how many use the old flight corridors cut by the traffic routes. The question of the extent to which the bridges influence the flight behavior of the bats with regard to the flight altitude and direction remains largely unresolved. So far, a study by the University of Leeds from 2012, which reproduces the relevant studies, is unique. However, this study is only representative to a limited extent with regard to the different species of bats and the types of bridges.
Study from the University of Leeds
In the study of the Institute of Integrative and Comparative Biology (Institute for Systems and Comparative Biology), investigations were carried out on four highly frequented, recently completed highways. The study includes several bat underpasses and bridges (all made of wire ropes with spherical reflectors) as well as some flight corridors cut by the newly constructed roads. Night vision devices and bat detectors were used to determine the number of crossing bats at all points over a longer period of time, as well as their species, flight altitude and lateral distance to the bridges.
The results of the investigations into the individual crossing aids vary greatly, but show the conditions under which the bat bridges and underpasses can help. The number of bats at two of the three underpasses was very low. The majority (69% and 96% respectively) of the animals that passed here ignored the underpasses, so that they - mostly dangerously low - flew over the roadway. The animals preferred the nearby flight corridors that were established prior to construction. The other underpass, which is directly in a flight corridor, was used by almost all (96%) crossing animals and the total number of passing animals was significantly higher.
Compared to nearby flight corridors, the number of bats that passed the roads at the bridges was comparatively small. In addition, most of the animals (different depending on the bridge, maximum 84%) also flew dangerously close to the road in the immediate vicinity of the bridges. In the case of one of the bridges, a small proportion of the bats (11%) flew less than 2 meters from the bridge and a further proportion (30%) less than 5 meters from the bridge, but these proportions were negligible for the other objects. The bridges were largely ignored by the bats. Furthermore, almost all animals flew extremely close to the roadway in the flight corridors. The diagram opposite shows that even a bridge that was only a few meters away from one of the cut flight corridors was only actually used by a few animals. The animals largely kept their flight corridors and ignored the bridges almost entirely.
The study says that the current crossing aids for bats completely miss their target and would not be heeded by the bats, but instead kept their old flight corridors. Underpasses and overpasses would only help if they were built directly into existing flight corridors and the bats did not have to change their altitude and direction. In addition, bridges made of wire ropes are ineffective, and more extensive structures such as green bridges are required. In addition, it was shown that an artificially created hedge that leads to one of the underpasses and should serve as a guideline was completely ignored by the animals. In addition, it was found that the altitude of the animals above the road depends heavily on the height of the embankments at the edge of the road, so that an increase in this could serve as a crossing aid.
Further investigations
Similar results as the study by the University of Leeds have also been carried out on behalf of the Association for Species, Environment and Nature Conservation. It was investigated to what extent bats use green bridges to connect their habitats and for hunting. The data was collected on a total of eight wilderness bridges over federal motorways and federal highways and compared with nearby road bridges over the traffic routes. Although the wildlife bridges were not primarily intended for bats use, large numbers of bats were counted. Species that are not native to the region have also been identified. During a total of 204 hours of observation, a total of 1209 bat contacts were recorded at the green bridges, which corresponds to 5.93 contacts per hour. The majority of dwarf and whiskered bats were registered. It is noticeable that the bridges themselves not only served as a connection between the habitats, but also as a hunting area for many species.
The analysis of the individual activities on the bridges shows a direct relationship between vegetation, width and spatial connection of the bridge and the use by bats. Such bridges, which offered a good connection to the surrounding woodland and other linear growths, show a significantly higher bat activity than bridges that ensured connection to only gaps or no guidelines at all. Likewise, generalized wide bridges also have higher bat contacts. The exceptions are bridges with a lack of spatial connection. The same can be seen in relation to the vegetation: the denser the growth on the bridges, the more bats could be observed. The wilderness bridge with the fewest contacts was a technical structure without any vegetation. With one exception, all of the technical structures examined showed significantly lower activity than green bridges. The bat contacts on wild bridges were 5.8 times higher than on technical road bridges.
public perception
Public opinions about the construction of bat bridges differ widely. In particular, the construction of the two bridges in Biberach an der Riss triggered a great national media coverage. Critics of the bridges - especially the taxpayer association - see a waste of tax money in the bridges. In this context, it is often criticized that bats, as flying animals, obviously do not need a crossing aid. For example, the Focus lists the construction project as a "bridge farce in Biberach" in the list of the "craziest cases of German tax fraud". The world speaks of "nonsensical bat bridges". The non-party district administrator of the Biberach district, Heiko Schmid, defends the bridges as the "cheapest [variant] of all" to protect the bats. The landscape ecologist Jürgen Trautner involved in the construction project admits that there is no information about the functionality. It is assumed, however, that the bridges are used by the animals. The Naturschutzbund Biberach criticizes above all that it was not involved in the planning of the construction project. A green bridge would have made more sense because it was more promising and also suitable for other animals - even if significantly more money should have been invested. Nevertheless, criticism about wasting tax money is inappropriate. There was also some criticism or lack of understanding among the local population. The functionality of the bridges is often called into question there. At the moment (as of July 2014) there are no results available to the public on the studies of bat activities on the bridge. The cost of the bridge, which costs around half a million euros, includes measures to analyze the use by bats.
In the United Kingdom, too, the bat bridges built there sparked a far-reaching discussion. The BBC reported several times on some of the bridges. The main focus of British coverage was the bridge in Dobwalls (Cornwalls) - by far one of the most expensive structures in Great Britain. Since the resident bat population is only about 40 individuals, the costs are around 27,000 pounds (about 34,000 euros) per individual. This sum in particular caused great indignation. The crossing aid in Porthmadog was also often criticized. The most expensive bat bridge in Great Britain was built there to protect around 450 specimens of the endangered Lesser Horseshoe Bat, which corresponds to a cost of around 1,500 pounds (about 1,900 euros). It was complained that no pedestrian crossing, but a bridge for bats was financed. In both cases, the buildings are defended by conservationists. The bridges served to protect endangered animal species that are extremely susceptible to traffic accidents. Furthermore, according to the responsible authorities, the bridges were the only option to unite the traffic routes with applicable EU law.
Individual evidence
- ↑ § 14 BNatSchG - individual norm
- ↑ § 15 BNatSchG - individual norm
- ↑ a b c Bat bridges cost £ 27k per animal . In: BBC News , October 22, 2009. Retrieved June 6, 2014.
- ↑ Un couloir à chauves-souris In: Sud Ouest . February 28, 2012. Retrieved July 8, 2014 (French).
- ^ Balbigny (Loire) - Un pont pour les chauves-souris au-dessus de l'A89 In: France 3 Rhône-Alpes . November 22, 2012. Retrieved July 8, 2014 (French).
- ↑ Marc Holderied, Gareth Jones, Otto von Helversen: Flight and echolocation behavior of whiskered bats commuting along a hedgerow: range-dependent sonar signal design, Doppler tolerance and evidence for 'acoustic focussing' . In: Journal of Experimental Biology . February 28, 2006. Accessed July 5, 2014 (PDF; 1 MB).
- ↑ a b Anna Berthinussen, John Altringham: Do Bat gantries and underpasses Help Bats Crossroads Safely? . Study from the University of Leeds . In: PLOS ONE . June 13, 2014. Accessed July 3, 2014.
- ↑ Lothar Bach, Heiko Müller-Stieß: Technical article bats on selected green bridges . November 2005. Retrieved July 7, 2014.
- ↑ These are the most insane cases of German tax fraud . In: Focus Online . October 17, 2013. Retrieved July 8, 2014.
- ↑ Nonsensical Bat Bridge and eKiosks . In: The world . October 17, 2013. Retrieved July 8, 2014.
- ↑ a b c District Administrator Heiko Schmid and landscape ecologist Jürgen Trautner on the bat bridges in Biberach In: SWR3 . October 25, 2013. Retrieved July 8, 2014.
- ↑ Controversial bat bridge: Why don't they fly over it? In: Badische Zeitung . November 3, 2013. Retrieved July 7, 2014.
- ↑ Statement by NABU Biberach In: NABU Biberach website , section bat bridges . Retrieved July 8, 2014.
- ↑ a b Biberach: 435,000 euros from taxpayers' money for bat bridges . In: German economic news . October 28, 2014. Retrieved July 8, 2014.
- ↑ a b £ 650k 'bat bridge' criticized in Porthmadog . In: BBC . September 22, 2014. Accessed July 6, 2014.