Conserving localized endemic butterflies through demographic and ecological studies: Polyommatus humedasae

1. Polyommatus humedasae is an endemic species narrowly distributed in a few sites in the Aosta Valley (NW Italy). Similarly to other alpine butterflies, the survival of the species is closely linked to the conservation of semi-natural grasslands. 2. Despite the species being known since 1976, this is the first comprehensive data collection and analysis on this species, firstly to understand its distribution. At Pont d’Ael, the species core site, we applied the mark-release-recapture (MRR) method to estimate population size and density. To understand the species ecology, we collected data on preimaginal stages (eggs and larvae), host plants, and vegetation composition. 3. The new data on species distribution (with 5 new sites and 2 subpopulations already extinct) permitted to update the extinction risk through IUCN assessment to Critically Endangered (CR). The estimated size (881 individuals) and density (73 N/ha) of the studied population are higher than those of other endemic Polyommatus species. Data suggest the species is monophagous on Onobrychis arenaria and prefers to lay eggs where the host plant is abundant, in ecotonal areas with some shrub cover (average 8 %), high herbaceous cover (average 68 %) and on plants in better physiological conditions. 4. For species such as P. humedasae, which are threaten by woody encroachment, climate change, fires and collection, we propose the application of a management plan that includes: 1) mechanical cut of wood species; 2) small herds on a rotational basis to reduce woody encroachment and maintain shrub patches; 3) dissemination events to highlight the population importance.