Federal Supreme Court, 24.11.2025, 1C_65/2025
Facts
A property owner is challenging a development plan by the municipality of Obersiggenthal to widen an existing path to create a new road access. This project affects his plot of land, which is home to a population of common midwife toads, a threatened and protected amphibian species.
The project would lead to a significant increase in traffic along the habitat of these amphibians. After his objection was rejected by the municipality, and his subsequent appeals were dismissed by the cantonal department and the Administrative Court of the Canton of Aargau, the owner appealed to the Federal Supreme Court.
Legal Analysis
According toArt. 18 para. 1 of the Federal Act on the Protection of Nature and Cultural Heritage (NCHA), the extinction of indigenous species must be prevented by preserving habitats (biotopes) of sufficient size. Any encroachment upon a biotope worthy of protection due to technical development is only permissible if, after weighing all competing interests, it proves unavoidable (Art. 18 para. 1ter NCHA). The intervention must be tied to a specific location and meet a compelling need (Art. 14 para. 6 of the Ordinance on the Protection of Nature and Cultural Heritage (NCHO)) (recital 1)
A biotope is considered worthy of protection even in the absence of formal classification, particularly if it houses threatened species listed on the FOEN Red Lists. Protection extends not only to the primary habitat (e.g., the spawning site) but also to terrestrial living spaces and the connecting corridors between them (recital 2.1).
If an encroachment is deemed permissible, the party responsible must take measures to ensure the best possible protection, restoration, or, failing that, adequate compensation (Art. 18 para. 1ter NCHA). Under the principle of coordination (Art. 25a of the Federal Act on Spatial Planning (SPA)), these measures must be defined and guaranteed at the zoning plan stage and cannot be deferred to the building permit procedure (recital 2.2).
In this case, the Federal Supreme Court acknowledges that the appellant's garden, which houses a population of common midwife toads, constitutes a biotope worthy of protection under the NCHA, even without formal designation. This protection includes the connecting corridor used by the amphibians to move, which would be crossed by the future road (recital 2.2).
Contrary to the lower courts, which had characterized the impact as "minimal," the Federal Supreme Court, aligning with the opinion of the Federal Office for the Environment (FOEN), considers the projected increase in traffic (from 20 to 100 vehicles per day) to be "more than minor." For a small population of a threatened species, the increased risk of mortality is significant and could have fatal consequences (recitals 3.3.1-3.4).
The Federal Supreme Court further identifies a major procedural flaw: the municipality failed to properly conduct the required weighing of interests. When examining various road access options, it neglected to incorporate the significant public interest of protecting the biotope. The comparison was limited to technical and economic criteria, without evaluating whether another option, also deemed "good" from a technical standpoint, would have been more respectful of the local wildlife. The public interest in the project's completion cannot, therefore, be classified as clearly overriding the protection of the threatened species (recitals 4.1-4.4).
Finally, the Federal Supreme Court reiterates that any potential protection or compensation measures (such as an amphibian crossing) must be defined in a binding manner within the development plan itself and not deferred to the future building permit procedure (recitals 5.1-5.2).
The Federal Supreme Court has upheld the appeal. It has set aside the decision of the Aargau Administrative Court and remanded the case to the municipality of Obersiggenthal. The municipality must now conduct a new review of the development options by performing a comprehensive balancing of interests, which must adequately include the public interest in protecting the biotope and the threatened species.
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