Habitat characterization of Saskatchewan's Dakota skipper, Hesperia dacotae population

Abstract

The Dakota skipper, Hesperia dacotae (Skinner, 1911) (Hesperiidae), is an at-risk butterfly species that inhabits the mesic mixed-grass prairie. The Dakota skipper is listed endangered under the federal Species at Risk Act. Loss of native prairie is the main factor driving declines in Dakota skipper habitat and species abundance is assumed to be declining. Currently, there is a knowledge gap pertaining to habitat associations and availability of Saskatchewan populations. This information is critical to construct a recovery plan to secure Dakota skipper populations. The first objective was to better understand the environmental associations of Dakota skipper habitat through landscape, vegetation, soil, climate, microclimate, and Hesperiidae butterfly species occupancy. Data collection was conducted in 2015 and 2016; of the 46 sites surveyed; nine were Dakota skipper positive (i.e., present) sites and 37 were negative (i.e., non-detect) sites. Results indicated that plant community composition was not a significant predictor of Dakota skipper presence, but three plant species were significantly associated with the species; Pediomelum argophyllum (Pursh) J.W.Grimes (Fabaceae), Zizia aptera (A.Gray) Fernald (Apiaceae), and Schizachyrium scoparium (Michx.) Nash (Poaceae). No soil or climate variables were significant predictors of Dakota skipper presence; however the species was significantly associated with steep slopes. Warmer maximum and average ground-level temperatures were also associated with Dakota skipper presence. The second objective was to determine Dakota skipper habitat suitability and distribution through a landscape-level habitat distribution model based on climate normal, soil, and landscape variables. Data were obtained from publically available Dakota skipper observation locations and in situ data collection within Saskatchewan. A total of 66 unique survey sites were obtained; 28 of these sites were Dakota skipper positive sites whereas the remaining 38 were negative sites. A habitat distribution map ranks the suitability of Dakota skipper habitat throughout southeastern Saskatchewan. Results indicated that although the Dakota skipper inhabits the mesic mixed-grass prairie region, only 11% of this region contains exceptional habitat (habitat probabilities 0.71-1) for this species. These areas contain a significantly lower mean diurnal temperature range and a higher ammonium soil content. I conclude that although the Dakota skipper inhabits the native mesic mixed-grass prairie region, environmental constraints including climate, soil, and landscape variables restrict this species to a more limited area of available habitat then initially thought. A landscape-level habitat suitability and distribution map complemented by habitat associations allows for more accurately targeted surveys, informs managers developing conservation and management plans, and allows for an overall better understanding of the Dakota skipper’s current situation in southeastern Saskatchewan. Findings indicate that additional Dakota skipper populations are likely in Saskatchewan and future targeted surveys will allow for a full evaluation of this species’ distribution and conservation status.