Declines of prairie butterflies in the midwestern USA

Published source details Swengel S.R., Schlicht D., Olsen F. & Swengel A.B. (2011) Declines of prairie butterflies in the midwestern USA. Journal of Insect Conservation, 15, 327-339.
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This study is summarised as evidence for the following.

	Action	Category
	Use rotational burning Action Link

Use rotational burning

A replicated, before-and-after, site comparison study in 1979–2009 in prairie, grassland and pine barrens in Illinois, Iowa, Minnesota and Wisconsin, USA (Swengel et al 2011) found that rotational burning, along with other interventions, had mixed effects on prairie-specialist butterfly abundance. At sites managed by rotational burning, the Ottoe skipper Hesperia ottoe declined over time in some sites in two of four states (Minnesota and Wisconsin), and the Poweshiek skipperling Oarisma poweshiek and Aphrodite fritillary Speyeria Aphrodite declined in sites in one state (Iowa). Regal fritillary Speyeria idalia numbers increased at one site in one state (Wisconsin). No changes were found for species monitored in other states. Results are presented as statistical tests. In four areas in Wisconsin designated as butterfly reserves (≤32% burned/year), Karner blue butterfly Lycaeides melissa samuelis abundance decreased less (1999: 27 individuals/km; 2009: 20 individuals/km) than at 10 sites where higher levels of burning, as well as timber extraction and public rights-of-way, were allowed (1999: 17 individuals/km; 2009: 2–5 individuals/km). Butterfly counts from 10 separate researcher teams, which overlapped in location, were combined and adjusted to account for differences in survey methods. At each site, 20–35% of the area was burned on average each year, with each section being burned at least every 10 years. Authors reported that sites were also managed with mowing, haying, brush-cutting and herbicides; details of management at each not provided.

(Summarised by: Eleanor Bladon)