Fledermausquartier Brauereikeller Frankfurt (Oder): A Protected Nature Reserve in Brandenburg

The protected area's history begins not with conservation, but with industrial decline. The Ostquell brewery on Frankfurt (Oder)'s Bahnhofsberg was built in the 19th century and shut down in 1950, after which its cellars and upper floors gradually deteriorated into a structurally unsafe but biologically valuable ruin. For decades, the brewery's abandoned vaults hosted small numbers of hibernating bats, but the ruin was open to the public and only secured by three steel doors. When the first systematic bat count took place in 1987, just 250 bats were recorded across the entire structure.

The turning point came in 1989, when citizens organized to oppose planned demolition of the ruin. That same year, and in 1990, the council of the Bezirk Frankfurt (Oder) issued initial protection orders safeguarding it as a bat sanctuary. In 1988 the first physical security measures began, and after 1989 a chain-link fence, donated by West Germany's BUND (Friends of the Earth), formalized the ruin's protection. The federal German conservation process formally opened in 1998, when the city issued an interim safeguarding ordinance that imposed a building moratorium on the ruin.

Bat numbers rose sharply after the ruin was secured, peaking at roughly 2,500 bats by the late 1990s before stabilizing at between 1,500 and 2,000. The site was designated as an FFH (Fauna-Flora-Habitat) area in 2000, a status its then-owner unsuccessfully challenged in administrative court. After protracted negotiations, the property was sold in 2003 to the EuroNatur foundation, with the purchase financed jointly by EuroNatur, the German Federal Agency for Nature Conservation (BfN), and the State of Brandenburg. In January 2003 the 1.34-hectare site was formally declared a Naturschutzgebiet, and the full nature reserve designation was completed on 26 January 2006. Since 2018 the site has been part of the German-Polish Interreg Natura Viadrina+ project focused on bats, and in summer 2021 a major structural rehabilitation of the ruin's roof and interior supports was completed.

The protected area's landscape is unusually compact and almost entirely built around a single human-made structure and its immediate setting. The reserve sits on the Bahnhofsberg, a slope above the Oder river in the center of Frankfurt (Oder), giving it an exposed, elevated position above one of Central Europe's most important river corridors. The brewery ruin itself is a multistory brick shell with deep, vaulted cellars that extend more than 1,150 square meters beneath the building, connected by passageways that allow bats to move between hibernation chambers.

The topography is shaped by the Oderhang, the river slope that rises steeply from the banks of the Oder. This topographic feature is essential to the site: the slope exposes the ruin to natural air drainage, moderates temperature extremes, and channels bat flight lines along the river. Surrounding the ruin, the city has established a 40-meter-wide green buffer strip in its local development plan to protect flight paths and prevent disturbance to the bats' microclimate.

Externally, the reserve blends into an urban landscape of late 19th- and 20th-century buildings, transport infrastructure (the Bahnhofsberg lies near the city's railway facilities), and the open corridor of the Oder river itself. This unusual juxtaposition, an industrial ruin serving as a wildlife sanctuary in the middle of a small European city, defines both the visual and ecological character of the protected area.

Although the reserve covers only about 1.34 hectares, its ecological character is defined less by spatial extent than by the microhabitat provided inside the brewery ruin. The frost-free cellar vaults, with stable temperatures around 5 degrees Celsius and humidity approaching saturation, replicate the cave-like hibernation conditions that bats depend on, but do so entirely within an urban historic structure.

The surrounding landscape adds complementary habitat elements. The Oder river corridor functions as a guiding flyway for bats moving between summer roosts and hibernation sites. The green buffer zone around the reserve, combined with the protection of flight lines and hunting areas in the city's planning documents, helps maintain connectivity between the ruin and broader foraging habitats such as the wetlands, woodland patches, and floodplain meadows of the Oder valley. The reserve itself contributes to the conservation of building-dwelling species: modifications to the ruin in 2021 added swift nest boxes and bat niches in the external facade, expanding its value beyond hibernation.

The microclimatic stability inside the ruin, and the layered offerings of deep cellar vaults, intermediate floors, and accessible roof spaces, collectively create a habitat gradient that supports different bat species in different ways, from deep torpor in the most stable lower chambers to more active roosting in upper levels.

The wildlife profile of the Fledermausquartier Brauereikeller Frankfurt (Oder) is dominated by bats, with more than 30 species documented in or near the ruin. The centerpiece of the roost is the Greater Mouse-eared Bat (Myotis myotis), for which the ruin is the largest known winter roost in Germany. In winter 2007/2008, 811 Greater Mouse-eared Bats were counted in the ruin, and the species has been recorded every winter as the most numerous occupant.

Four species occur consistently every winter: Greater Mouse-eared Bat, Natterer's Bat (Fransenfledermaus), Daubenton's Bat (Wasserfledermaus), and Brown Long-eared Bat (Braunes Langohr). Other notable species recorded in the roost include the Pond Bat (Teichfledermaus), Bechstein's Bat (Große Bartfledermaus), and Natterer's/Klein's bat complex (Kleine Bartfledermaus). Banding studies have shown that Greater Mouse-eared Bats hibernating here originate from summer colonies in western Poland, with ringed individuals later recaptured as far away as the Müritz lake district and the Czech Republic, illustrating the ruin's role in a wider Central European bat network.

The protected area also supports breeding birds adapted to old buildings: swift (Mauersegler) nest boxes were fitted to the ruin's exterior during 2021 renovation work, expanding the site's wildlife value beyond hibernating bats. Beyond the ruin itself, the reserve is embedded in a network that protects White Storks, Fire-bellied Toads (Rotbauchunke), and Smooth Snakes (Schlingnatter) under the Interreg Natura Viadrina+ project.

The Fledermausquartier Brauereikeller Frankfurt (Oder) is a nationally and internationally significant conservation site. It is formally protected as a Naturschutzgebiet (nature reserve) under Brandenburg law, formally designated in 2003 and legally completed on 26 January 2006, with a total area of 1.34 hectares. The site is also designated as a Fauna-Flora-Habitat (FFH) site under the EU Habitats Directive, recognized since 2000 with a 0.25-hectare core area, and is classified in international databases as IUCN Category IV (Habitat/Species Management Area).

Its conservation value rests on the irreplaceable role of the brewery ruin as a hibernation site for bats, particularly the Greater Mouse-eared Bat, which is considered vulnerable across much of its range. Protection extends beyond the structure itself. Frankfurt (Oder)'s planning regulations impose a 40-meter green buffer around the ruin, restrict building heights and setbacks to preserve known flight paths and hunting grounds, and prohibit changes that would alter the microclimate inside the cellar vaults. These legally binding controls have already prevented at least one major development, an 8-story parking garage originally planned within 10 meters of the ruin, from interfering with bat flight lines.

Conservation management is collaborative and cross-border. The site is owned by the EuroNatur foundation and has received restoration and protection funding from the German Federal Agency for Nature Conservation (BfN) and the State of Brandenburg. Day-to-day stewardship is handled by the Landschaftspflegeverband Mittlere Oder, while the ongoing protection of bats in the ruin is integrated into the larger German-Polish Interreg Natura Viadrina+ project, which links the site to broader conservation efforts along the Oder and the Festungsfront Oder-Warthe-Bogen.

The site sits at an unusual intersection of industrial heritage and modern conservation culture. The Ostquell brewery, built on the Bahnhofsberg in the 19th century and shuttered in 1950, embodies the post-war industrial collapse of the GDR era. During GDR times, the upper floors were repurposed by a neighboring leisure business as storage for adhesives, lacquers, and paints, leaving the structure in increasingly fragile condition.

Its conservation story is itself a piece of late-20th-century German cultural history. The citizens' initiative formed in 1989 to block demolition came at a pivotal moment, just months before German reunification, and the subsequent cross-border support from West Germany's BUND in installing protective fencing symbolizes the broader East-West environmental partnerships of that era. The legal struggles over the property, including disputes with the re-formed Ostquell-Brauerei AG and administrative court battles over FFH designation, became part of the wider narrative of how post-reunification Germany integrated East German industrial sites into European conservation law.

The site is also part of Frankfurt (Oder)'s broader sense of place. Together with neighboring protected areas such as the Booßener Teichgebiet, Eichwald und Buschmühle, Fauler See/Markendorfer Wald, Mittlere Oder, Oberes Klingetal, and Oderwiesen nördlich Frankfurt, the Brauereikeller represents one of the city's most distinctive natural-cultural landmarks: a ruin whose ecological future has been deliberately chosen as part of the city's identity.

Among the protected area's standout qualities is the sheer ecological density of a very small footprint: just 1.34 hectares containing what is currently the largest known winter roost of the Greater Mouse-eared Bat in Germany. More than 30 bat species have been recorded, with at least four present every winter, and banded bats ringed in the ruin have been recovered from western Poland, the Müritz, and the Czech Republic, underscoring its importance as a node in a transnational bat network.

The reserve's conservation history is itself a highlight. Saved from demolition in 1989 by a citizens' initiative and protected successively through GDR-era district orders, post-1990 federal safeguarding ordinances, FFH designation in 2000, and full nature reserve status in 2003–2006, the site stands out as an example of long-term, layered legal protection. Its acquisition by the EuroNatur foundation in 2003 and integration into the cross-border Interreg Natura Viadrina+ project give it a uniquely international conservation profile.

Physically, the site is unusual: an urban ruin in the center of Frankfurt (Oder) whose cellar vaults, with stable temperatures of around 5 degrees Celsius and near 100 percent humidity, replicate cave-like hibernation conditions within a 19th-century brick shell. The 40-meter planning buffer, legal flight-path protections, and 2021 renovation that added bat niches and swift nest boxes all make it a model of how a single industrial ruin can be transformed into a functioning modern wildlife sanctuary.

The Fledermausquartier Brauereikeller Frankfurt (Oder) is best appreciated during the cooler months, when the ruin's bat populations are at their highest. Winter is the peak season for observing bat abundance inside the cellar vaults, although the protected ruin is not normally open to visitors and observation is generally limited to conservation-led activities and research counts rather than public access.

For visitors interested in the broader setting, spring and early summer allow easier walking in central Frankfurt (Oder) and along the Oder river slope to view the brewery ruin and its urban context, while milder weather highlights how the surrounding city integrates with the protected buffer zone. Late autumn, before the bats settle into full hibernation, can be a period when researchers are most active at the site. Because the protected area is small, structurally sensitive, and primarily a conservation and research site, planning a visit around educational interpretation or guided conservation events, rather than mass tourism, is generally the most appropriate approach.