Survey of regal fritillaries (Speyeria idalia) in the northern Loess Hills of western Iowa – A comparison of prairie size with fritillary abundance

Background/Question/Methods

Today, less than 0.1% of Iowa’s original tallgrass prairie remains. A consequence of this historic loss of grassland habitat is the risk to prairie-associated organisms, such as butterflies. This is especially true for remaining populations of butterflies that depend on tall grass prairie habitat such as the regal fritillary (Speyeria idalia). The purpose of this study was to survey butterflies on five undisturbed native tall grass prairies of various sizes the Loess Hills in western Iowa. Although my surveys of butterflies included all species, I specifically focused on the regal fritillary (S. idalia), a species whose recent decline has been documented throughout much of its range. In July of 2017 and 2019 tallgrass prairies were surveyed in Plymouth and Woodbury counties using the Pollard walk.

Results/Conclusions

Speyeria idalia was observed on all sample locations. Also, there was little correlation between prairie size and regal fritillaries observed (r = 0.03) in 2017. However, in 2019 there was a significant positive correlation between prairie size and the number of regal fritillaries observed (r = 0.91, P< 0.05). Furthermore, there was a high abundance of regal fritillaries on prairies less than 65 ha in total area. This contrasts with the minimum viable prairie size reported for S. idalia populations in Iowa and Pennsylvania. I hypothesize that the quality of the prairie or the disturbance regime may play a greater factor than prairie size in influencing S. idalia populations.