Life history and ecology of the endangered Poweshiek skipperling Oarisma poweshiek in Michigan prairie fens

Poweshiek skipperling (Oarisma poweshiek, Lepidoptera: Hesperiidae) has experienced a range-wide decline resulting in six reported extant sites. Critical knowledge gaps related to Poweshiek skipperling adult behavior, phenology, habitat structure, and potential larval host plants are limiting the ability to manage this federally endangered species. To address these information needs, we conducted extensive surveys in the last remaining stronghold of four extant prairie fens in Michigan. We used point transect surveys to collect data on plant structure, and Poweshiek skipperling behavior and detection. We estimated Poweshiek skipperling abundance and modeled the influence of local vegetation on Poweshiek skipperling presence/absence. We estimated the abundance of adult Poweshiek skipperling in Michigan prairie fens to be 231 (95% CI 160–332), further highlighting the imperiled status of this species. Presence of Poweshiek skipperling along our transects was negatively associated with obstructive vegetation and positively associated with the availability of the nectar source Dasiphora fruticosa. Our observation data indicated females nectared most frequently on D. fruticosa, whereas males nectared most often on Rudbeckia hirta. Across the field season we observed 7 oviposition events on four plant species (Muhlenbergia richardsonis, Muhlenbergia glomerata, Carex sterilis, and D. fruticosa), three of which had no previous documentation as a possible host plant. Results from this study can be used to evaluate management decisions and inform both in situ and ex situ conservation efforts. It is critical to continue monitoring remaining populations, not only to assess conservation efforts, but also to discern the patterns and processes influencing species extinction.