Effects of fire and hay management on abundance of prairie butterflies

Published source details Swengel A.B. (1996) Effects of fire and hay management on abundance of prairie butterflies. Biological Conservation, 76, 73-85.
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This study is summarised as evidence for the following.

	Action	Category
	Use rotational burning Action Link
	Change mowing regime on grassland Action Link
	Use rotational mowing Action Link
	Use prescribed fire to maintain or restore disturbance in grasslands or other open habitats Action Link

Use rotational burning

A replicated, site comparison study in 1988–1993 in 51 tall-grass prairies in Illinois, Iowa, Minnesota and Wisconsin, USA (Swengel 1996) found that the abundance of prairie specialist butterflies in burned prairies increased with time since the last fire, but the abundance of other species was highest sooner after burning. At sites burned >4 years ago, the total abundance of six prairie specialists (75 individuals/hour) was higher than at sites burned the previous winter (10 individuals/hour). However, the abundance of grassland species and generalists was higher in the third year after burning (100–130 individuals/hour) than in the first or second year (50–100 individuals/hour) or fourth or fifth year (60–90 individuals/hour). The abundance of migrant species was higher in the year immediately after burning (770 individuals/hour) than in any subsequent year (10–40 individuals/hour). See paper for individual species results. Fifty-one sites (1–445 ha) were primarily managed by cool-season fire covering 5–99% of the site. From June–August 1988–1993, butterflies were surveyed 1–4 times/year on a transect through most sites (only Minnesota and Wisconsin in 1988–1989). Transects were sub-divided by the most recent management. Thirty-two species observed >49 times and at >5 sites were included, and divided into “prairie specialists” (6 species, only found on prairies), “grassland species” (13 species, found in prairies and other grasslands), “generalists” (10 species, found in grasslands and other habitats) and “migrants” (3 species, only present in the study area during the growing season).

(Summarised by: Andrew Bladon)
Change mowing regime on grassland

A replicated, site comparison study in 1992–1993 in 42 tall-grass prairies in Missouri, USA (Swengel 1996) found that prairie specialist butterflies were more abundant in hayed than burned prairies. In the year following haying, the abundance of prairie specialist butterflies (81 individuals/hour) was higher than two years after haying (68 individuals/hour), and both were higher than at sites the year after burning (2 individuals/hour), or two years after burning (21 individuals/hour). However, generalist and migrant species were less abundant at hayed sites (6–19 individuals/hour) than burned sites (18–24 individuals/hour). See paper for individual species results. Among 42 sites (6–571 ha), some were primarily managed by summer haying on a 1–2 year rotation with occasional cattle grazing, and some were managed by cool-season fire covering 5–99% of the site. In June 1992–1993, butterflies were surveyed at least once/year at most sites, either along a transect (35 sites) or from a single point (7 sites, recording only regal fritillary Speyeria idalia). Transects were sub-divided by the most recent management. Sixteen species observed >49 times and at >5 sites were included, and divided into “prairie specialists” (only found on prairies), “grassland species” (found in prairies and other grasslands), “generalists” (found in grasslands and other habitats) and “migrants” (only present in the study area during the growing season).

(Summarised by: Andrew Bladon)
Use rotational mowing

A replicated, site comparison study in 1992–1993 in 42 tall-grass prairies in Missouri, USA (Swengel 1996) found that butterflies were more abundant in the first year after haying than in the second year after haying. In the first year following haying, the abundance of prairie specialist butterflies (81 individuals/hour) was higher than two years after haying (68 individuals/hour). The abundance of grassland species (11 individuals/hour), generalists (17 individuals/hour) and migrants (19 individuals/hour) in the year following haying was also higher than two years after haying (grassland: 9; generalist: 10; migrant: 5 individuals/hour). See paper for individual species results. Of 42 sites (6–571 ha), some were primarily managed by summer haying on a 1–2 year rotation with occasional cattle grazing (number not given). In June 1992–1993, butterflies were surveyed at least once/year at most sites, either along a transect (35 sites) or from a single point (7 sites, recording only regal fritillary Speyeria idalia). Transects were sub-divided by the most recent management. Sixteen species observed >49 times and at >5 sites were included, and divided into “prairie specialists” (only found on prairies), “grassland species” (found in prairies and other grasslands), “generalists” (found in grasslands and other habitats) and “migrants” (only present in the study area during the growing season).

(Summarised by: Andew Bladon)
Use prescribed fire to maintain or restore disturbance in grasslands or other open habitats

A replicated, site comparison study in 1992–1993 in 42 tall-grass prairies in Missouri, USA (Swengel 1996) found that two prairie specialist butterflies were less abundant, but generalist and migrant species were more abundant, in burned than in hayed prairies. At sites managed by burning, the abundance of two prairie specialists (regal fritillary Speyeria idalia and arogos skipper Atrytone arogos; 2–21 individuals/hour) was lower than at sites managed by haying (68–81 individuals/hour). However, generalist and migrant species were more abundant at burned sites (18–24 individuals/hour) than hayed sites (6–19 individuals/hour). See paper for some individual species results. Of 42 sites (6–571 ha), some were managed by cool-season burning covering 5–99% of the site, and the rest by summer haying on a 1–3 year rotation with occasional cattle grazing (number of sites in each management not given). In June 1992–1993, butterflies were surveyed at least once/year at most sites, either along a transect (35 sites) or from a single point (7 sites, recording only regal fritillary). Sixteen species observed >49 times and at >5 sites were included, and divided into “prairie specialists” (only found on prairies), “grassland species” (found in prairies and other grasslands), “generalists” (found in grasslands and other habitats) and “migrants” (only present in the study area during the growing season).

(Summarised by: Andrew Bladon)