Grass-skipper (Hesperiinae) trends in midwestern USA grasslands during 1988–2013

Abstract

We surveyed butterflies in prairies, pine-oak barrens, and degraded grasslands during 1988–2013 in southern Wisconsin, USA. In prairie preserves (primarily managed with frequent fire), both specialist and non-specialist “grassland” grass-skippers declined strongly. Specialists inhabiting the native herbaceous flora of pine-oak barrens that had little management but relatively consistent vegetation over time had large fluctuations but more stable trends. Grassland grass-skippers showed similar more stable trends in barrens and degraded fields with relatively consistent vegetation over time. Significant population trends did not relate clearly to how southerly the species’ ranges are. Specialist and grassland grass-skipper persistence after prairie preservation correlated negatively with both number of years since preservation and prairie patch size. We also analyzed grass-skipper abundance during 1977–2012 in midwestern 4th of July Butterfly Counts, an annual volunteer butterfly census. Specialists declined significantly but grassland as well as forest and wetland grass-skippers averaged a non-trend. We hypothesize that the reasons why fire management is adverse are because of direct mortality and also the thick tall grass regrowth, which may be unsuitable for larvae to use. It appears urgent to identify and implement management strategies in prairie preserves that consistently maintain grassland vegetation as required by grass-skippers in ways the grass-skippers themselves tolerate.