Réserve naturelle régionale des Grottes du Cirque: Protected Limestone Karst Landscapes and Cave Habitats

The caves of the Cirque area have long held scientific interest, particularly the Grotte aux Ours, whose cave bear deposits have made it a recognized paleontological and archaeological site. Before formal protection, however, the site was vulnerable, and a history of unregulated access led to the pillaging of important fossil material.

The reserve's formal conservation history began in 1988 with classification as a Réserve naturelle volontaire, a voluntary nature reserve under French law. This protection ended after the 2002 loi Démocratie de proximité, which reassigned certain environmental competencies to regional authorities and caused the old voluntary reserve designation to lapse. Several sites important for bats temporarily lost their protected status during this transition.

In response, the CPEPESC Franche-Comté, working closely with the former Franche-Comté region, explored creating a network of regional nature reserves dedicated to chiroptères and their habitats. This effort succeeded in 2015 and 2017, when seven such reserves were established. The Grottes du Cirque was officially reclassified as a Réserve naturelle régionale on 24 September 2015 by regional council deliberation. A unified management plan for the entire cave network was later approved unanimously by the Bourgogne-Franche-Comté regional council in September 2019, providing the first formal framework for the conservation of these underground habitats.

The reserve occupies a compact segment of the pre-Jura hills, dominated by a classic Jill-shaped valley known locally as a reculées. This landform, a steep-sided, horseshoe-shaped valley that opens abruptly out of the plateau, is a defining feature of the region's karst terrain and shapes both the visible scenery and the underground hydrology of the area.

The caves themselves are formed in Middle Jurassic limestone, with strata dating from the upper Bajocian period. An extensive oolithic limestone sequence is exposed at the foot of the valley, and a particularly complete stratigraphic section, including the Bajocian and adjacent formations, is visible near the remains of an old quarry. The combination of surface relief and soluble bedrock has produced not only the visible cliffs and slopes of the reculées but also the six protected cavities: dry caves, fossil-rich chambers, and an active resurgence where the underground river Seris emerges.

The overall setting is one of mixed forested slopes enclosing a sheltered, south-facing valley. The karst topography, the limestone exposures, and the presence of both dry chambers and a flowing underground river together create a varied micro-landscape in a very small area, making the site as much a geological attraction as a biological one.

Ecologically, the reserve is built around a network of underground habitats that together form a coherent system for cave-dwelling fauna, particularly bats. Above ground, the surrounding slopes and forests provide complementary habitat for the species that use the caves seasonally for hibernation or summer roosting.

The soils, vegetation, and forest cover of the reculées are also part of the reserve's ecological value. The site's management plan explicitly recognizes significant forest habitats, and efforts to protect bat foraging areas extend beyond the cave entrances into the surrounding woodlands. The karst geology also influences hydrology and microclimate within the valley, generating the stable, humid conditions that underground species require.

Although the reserve is small in area, its ecological significance is regional rather than local. By linking six nearby but distinct cavities into a single protected unit, it creates functional redundancy for the bat species that depend on multiple roost sites through the year, reducing the risk that any single disturbance could have disproportionate effects on hibernating or maternity colonies.

The wildlife focus of the reserve is almost entirely on bats, particularly the species that hibernate in the protected caves. The most important populations are those of the Lesser Horseshoe bat (Rhinolophus hipposideros) and the Greater Horseshoe bat (Rhinolophus ferrumequinum), both of which are considered vulnerable or endangered on the regional red list for Franche-Comté. The Greater Horseshoe bat is especially significant at a regional scale, with the Grottes du Cirque forming part of an important network for this species.

In addition to the horseshoe bats, the caves shelter a diverse community of Vespertilionid bats, with at least nine species recorded in the cavities. Among these, the Greater Mouse-eared bat (Myotis myotis) and the Western Barbastelle (Barbastella barbastellus) are particularly noteworthy, the latter being a species of high conservation concern across Europe. Across the associated network of cave reserves, six priority species are targeted for conservation: Schreiber's Bent-winged bat (Miniopterus schreibersii), the Lesser Mouse-eared bat (Myotis blythii), the Mediterranean Horseshoe bat (Rhinolophus euryale), the Greater Horseshoe bat, the Lesser Horseshoe bat, and the Geoffroy's bat (Myotis emarginatus).

Access restrictions on the caves reflect the sensitivity of underground bat colonies. Human disturbance during hibernation or summer roosting can cause mortality or force colonies to abandon favorable sites for less suitable ones, which is why all of the cavities are closed to the public year-round except under carefully controlled conditions.

The reserve was created specifically as part of a coordinated regional strategy to protect cave-dwelling bats and the underground habitats on which they depend. Rather than functioning as a standalone site, Grottes du Cirque is one of seven reserves making up a Franche-Comté network of protected cavities designed to safeguard chiroptères through protection of roosting sites, foraging habitats, and the broader forest environment.

Conservation efforts at the site are grounded in a formal management plan adopted unanimously by the Bourgogne-Franche-Comté regional council in 2019. This plan identifies the preservation of functional roosting networks for six priority bat species as the main conservation objective, with nearly seventy planned actions designed to maintain or improve habitat conditions. These actions also incorporate conservation of associated remarkable forest habitats in the surrounding area.

The reserve is also recognized through additional protection tools at both national and European levels. It is designated as a ZNIEFF type I area under the name Grotte aux Ours, and as a Réserve naturelle régionale it carries a strict legal framework for regulating access, disturbance, and habitat modification. The Grotte aux Ours is sealed with a metal gate to prevent both bat disturbance and the loss of its remaining paleontological material.

Although small in size, the site carries a strong cultural and scientific identity rooted in the long history of cave exploration in the Jura region. The Grotte aux Ours has been recognized for generations as an important paleontological locality, having yielded one of the most significant cave bear deposits in eastern France, including the unusual discovery of a nearly complete newborn cave bear skeleton.

This fossil heritage, however, has been damaged in the past by unauthorized collection, a history that directly informs the reserve's strict access policy today. Visits to the cavities are limited or prohibited year-round, with only the resurgence of the Seris underground river open to authorized visitors between late April and late October, and only with permission from the commune of Gondenans-les-Moulins. In this sense, the reserve reflects a broader shift in how underground heritage sites in France are managed, emphasizing scientific protection and ecological sensitivity over casual exploration.

The reserve's standout features include six closely linked limestone caves within a single pre-Jura reculées, offering a rare combination of geological, ecological, and paleontological interest. The Greater and Lesser Horseshoe bats are the most emblematic species, supported by a community of at least nine Vespertilionid bats across the cave network. The Grotte aux Ours adds a strong paleontological layer, holding a major cave bear deposit that places the reserve among the important prehistoric sites of eastern France. Together, these qualities make the site an unusually dense example of protected underground heritage within the French regional reserve system.

Public access to the reserve is extremely limited and is centered on the resurgence of the Seris underground river, which is open only between late April and late October, and only with prior authorization from the commune of Gondenans-les-Moulins. Outside this window, the caves are closed to protect hibernating bats and sensitive underground habitat. For visitors interested in the broader landscape of the pre-Jura hills, late spring through early autumn is the most comfortable period, when the forested slopes and the entrance area of the reculées are most accessible and bat colonies are in their active season rather than in vulnerable hibernation.