Reviving of Coenonympha oedippus: A comprehensive approach to the reintroduction of an endangered European butterfly

In this study, we focus on Coenonympha oedippus, an endangered butterfly species protected under Annexes II and IV of the EU Habitats Directive. Predominantly inhabiting semi‐open wet grasslands across Europe, this species also occupies abandoned sub‐Mediterranean dry grasslands. Ecological distinctiveness in its habitat use is reflected in differences in larval host plants, wing morphology and genetic composition, resulting in two ecotypes: wet and dry. Notably, by 2018, only one population of the wet ecotype survived in Slovenia, necessitating reintroduction as a critical strategy to avert its national extinction. Building on our conservation objectives, we implemented a 5‐year project (2018–2022) to develop protocols for source individual and substrate collection, ex situ breeding in semi‐natural conditions, thorough release and post‐release monitoring. Our efforts included breeding from 18 females, yielding 754 eggs in a breeding house. From these, we successfully reared and released 460 individuals, comprising 419 pupae and 41 butterflies. The project culminated with promising outcomes: the reintroduced population exhibited an 87% growth rate, while the source population, following its last reinforcement, showed a 79% increase. The project success can be attributed to a comprehensive understanding of species' ecological requirements and the establishment of a long‐term management plan. Key to our approach was adaptive management, which allowed for flexibility and refinement of protocols during implementation. Meticulous documentation and evaluation of all project activities were instrumental, culminating in the production of standardised annual reports. Additionally, the project was bolstered by strong collaboration among scientists, site managers, government agencies and national media.