An Assessment of Prairie Management Practices for Maintaining Habitat Quality for the Endangered Poweshiek Skipperling Butterfly in Canada

Abstract

The Poweshiek skipperling (Oarisma poweshiek) was once a common prairie butterfly in central North America, but is now critically endangered in Canada and the United States. The Poweshiek skipperling is confined to the largest remaining tall grass prairie in Canada, which is currently managed using grazing and fire to maintain prairie habitat and prevent forest and shrub encroachment. To support re-introduction, restocking, and recovery of this critically endangered species, it is necessary to understand the habitat conditions preferred by skipperlings. By surveying prairie sites with Poweshiek skipperling across age and treatment categories (1-2 y since burn, 4-6 y since burn, .15 y since burn, and grazing), we identified commonly-used nectar plants and recorded physical variables known to influence plant diversity. We measured soil variables, including macronutrients, compaction, pH, texture, and moisture content, and used multivariate statistics to test for significant differences in site characteristics and plant community across treatments. For each site, we captured plant diversity, abundance, and cover, as well as total plant biomass. We found the oldest burn sites had the fewest skipperlings. Intermediate burn sites and lightly grazed sites contained the most skipperlings. In 95% of nectaring observations, adult skipperlings were feeding on Black-eyed Susan (Rudbeckia hirta), upland white aster (Solidago ptarmicoides), and Self-heal (Prunella vulgaris). Characteristics in the physical components of sites and plant communities did not significantly differ across treatment types for most variables with the exception of the oldest burns, which showed significantly higher levels of soil compaction, live biomass, bare ground, less flowering species during the flight period, less flowering stems, and increased presence of nonnative and invasive species. Poweshiek skipperling is at high risk of imminent extirpation, and we recommend that the management regimes be adjusted to plan for a consistent supply of habitat conditions and plant species composition exemplified by our intermediate burn sites. We suggest fire return intervals of 4-6 y using patch burns in combination with grazing, permitted at times that minimize the impact on immature stages of Poweshiek skipperling. This management is needed to provide suitable habitat conditions to maintain the current population and allow for successful restocking and recovery.

Endangered Oarisma poweshiek larvae vary their graminoid forage in Manitoba, Canada

“…Sites in Manitoba that had been intentionally burned approximately three to six years earlier supported relatively higher abundances of Poweshiek skipperlings than did sites with more recent and older burns and sites where grazing took place (Dupont-Morozoff et al 2022). Disturbances such as a cutting actionhayingand prescribed burns may improve the suitability of habitats for butterflies (Swengel 1996;Thom and Daniels 2017) but ought to be compatible with the life history of these same butterflies to reduce mortality (Swengel andSwengel 1999, 2015).…”

Management practices benefit endangered Poweshiek skipperling (Oarisma poweshiek) in Manitoba tall grass prairie

“…Gray), and little bluestem (Schizachyrium scoparium (Michs.) Nash) (Dupont Morozoff 2013;Henault and Westwood 2022). Larvae feed on host plants throughout the remainder of the summer and enter a form of dormancy as larvae in mid-to-late September (K. Eckhardt (personal communication, 24 October 2023)), overwintering at the base of host plant species in or above the litter layer (Borkin 1995;Selby 2005;Henault and Westwood 2022).…”

“…Gray) B. Boivin) have been the primary nectar plants of adults in Manitoba (Catling and Lafontaine 1986;Semmler 2010;Dupont Morozoff 2013;Westwood et al 2020), though Poweshiek skipperling have recently been observed nectaring on other species (Henault 2021). Catling and Lafontaine (1986) observed the highest Poweshiek skipperling densities in areas with high pale-spiked lobelia densities, but pale-spiked lobelia was not present during Semmler (2010) and Dupont Morozoff's (2013) studies and was also scarce in Henault's (2021) study. In Michigan, Poweshiek skipperling are more likely to be found in areas with high numbers of their preferred nectar plants (Belitz et al 2019).…”

“…The cause(s) of the recent rapid Poweshiek skipperling population decline in Manitoba are not well understood. Previous range contractions in the United States have been attributed to inadequate or inappropriate management resulting in unsuitable habitat (Swengel et al 2011), though there are mixed results on the impacts of management (e.g., prescribed burning and grazing) on Poweshiek skipperling abundance (Royer and Marrone 1992;Swengel 1998;Swengel and Swengel 1999;Dupont-Morozoff et al 2022). Prior to European colonization, the tall grass prairie was maintained by periodic wildfires and bison (Bison bison bison Linnaeus, 1758) grazing that suppressed ecological succession to shrubby habitat and reduced plant litter (Knapp et al 1999;Allen and Palmer 2011).…”

“…For Poweshiek skipperling, there are several limiting factors (e.g., isolated population, limited dispersal ability, a single generation per year) that make them particularly susceptible to excessive prescribed burning (e.g., burning that is too frequent, poorly timed, or too intense) (Swengel et al 2011) because these factors are associated with slow population recolonization and recovery if the population is reduced (Swengel 1996;Panzer 2002). Altered floral composition within burned areas (Howe 1995;Towne and Kemp 2008) may also result in several years before the floral community is suitable to skipperling again (Swengel 1996;Dupont Morozoff 2013). Previous studies have shown it typically takes 2-5 years for Poweshiek skipperling and other butterflies to recover post-burn (Swengel 1996;Panzer 2002), but some species were not fully recovered after 5 years (Vogel et al 2010).…”