Many native prairie butterfly species are highly at-risk due to habitat loss from agriculture. In western Washington, less than three percent of original prairie remains, with much of the former prairie grazed by cattle. This study aimed to understand how cattle grazing management strategies influence butterfly behavior and diffusion rates. We conducted behavioral experiments with two species of common native butterflies (Glaucopsyche lygdamus and Coenonympha tullia) at two native prairies with no grazing (high butterfly resource availability); two pastures grazed according to “conventional” management (low resource availability); and two pastures grazed according to “conservation” management (intermediate resource availability). We followed individuals for up to 60 minutes and recorded their behavior and location every 15 seconds. We recorded the nectar and host plant abundance at four randomly chosen points in each flight path. Using the turning angles and length of steps in the flight paths, we calculated diffusion rates for each individual and compared rates using a generalized linear mixed model with management type as an a priori fixed effect and site as a random effect. Then we conducted exploratory data analysis with forward model selection.
Results/Conclusions
We found that butterfly diffusion rates differed by sex, species, and management type. The diffusion rates of females of G. lygdamus were highest in conventional grazing (2.92-7.73 m2/s), lowest in native prairie (0.33-0.83 m2/s), and intermediate in conservation grazing (0.21-6.7 m2/s). Diffusion rates of females of C. tullia were lowest in native prairie (1.51-5.51 m2/s), highest in conventional grazing (1.41-12.87 m2/s) and intermediate in conservation grazing (0.33-12.2 m2/s). Diffusion rates of males of both species showed little difference based on management type. Our forward model selection indicated that nectar and host plant availability were two important predictors of diffusion rates. G. lygdamus depended in part on the presence of nectar plants Camassia quamash and Ranunculus occidentalis and the amount of the host plant Lupinus albicaulis. C. tullia diffusion rates seemed to depend mostly on the presence of the nectar plant Leucanthemum vulgare. This research suggests that butterflies may recognize conservation grazing management as higher quality habitat than conventional grazing and therefore conservation grazing may contribute to butterfly habitat.