In the face of butterfly species extinction on Seychelles and Mascarene archipelagos, there is an urgent need of increasing our knowledge about species, especially those which have been extinct from one island. Here, we focus on Antanartia borbonica (Oberthür, 1880), a threatened Mascarene butterfly, extinct from Mauritius and considered locally endangered (EN) on Réunion by the French IUCN committee. On Réunion, we investigated the way A. borbonica distribution changes throughout the year depending on elevation and temperature. We confirm previous observations suggesting a seasonal displacement along the elevational gradient: A. borbonica spends the winter in low-elevation areas and moves to higher ones during summer. This biological trait implies conservation actions considering the restoration of suitable habitats for this species along the elevational gradient. The priority, to ensure the long-term conservation of this species, is to create refuges especially in urban and secondary habitats located in lowland areas where relatively preserved ecosystems no longer exist.