Vegetation structure and time since fire predict the presence of the regal fritillary butterfly (Speyeria idalia) in Missouri

The regal fritillary is a prairie-specialist butterfly whose declining distribution is linked to habitat loss and declining grassland quality. Missouri’s proximity to the prairie/woodland transition and its seemingly stable regal populations makes it a unique and important region for studying habitat use and management. This study aims to quantify current regal population sizes within Missouri’s grasslands, and compare these population sizes with environmental covariates. Research was conducted at 159 management units across 54 grassland preserves. Regal fritillary presence, floral resources, and vegetation structure were quantified along transects centered within management units. Regal fritillary adults were not detected at the southernmost prairies of Missouri, despite historic observations, while the occupancy rate increased further north. Regal fritillary butterflies were more often present in grasslands with higher percent cover of flowering forbs, lower percent cover of grass and litter, lower litter depth, and lower vegetation height and density. For the grasslands managing with prescribed fire, regal fritillary butterflies were less likely to be found in management units that were burned three to five years ago when compared to shorter fire return intervals. Our data suggests that management which promotes shorter and less dense vegetation should be effective for conserving regal fritillary populations in Missouri, including small-scale rotational burning.