Butterflies, Cows and Caterpillars: Can Cattle Grazing Help Butterflies?, Post by Samantha Bussan, Photos by Samantha Bussan and Christopher Jason.
Samantha Bussan is a PhD Candidate in Cheryl Schultz’ Conservation Biology Lab at Washington State University Vancouver. Her work is focused on conserving native species in working lands. She can be contacted with further questions at firstname.lastname@example.org.
Butterflies, Cows and Caterpillars: Can Cattle Grazing help Butterflies?
Fields full of cows are a familiar sight around the South Puget Sound. But did you know that much of what is now pasture used to be prairie? South Puget Sound prairies have suffered a dramatic decline since European settlement due to fire suppression, urbanization, and conversion to agriculture. This severe habitat loss puts many native plants and animals at risk of extinction. Some people believe that the only way to provide habitat for these plants and animals is to remove cattle grazing and restore the prairies.
However, there is research showing that cattle grazing may benefit grassland butterflies, plants, and many other groups by increasing plant community diversity and the proportion of flowering plants, and by preventing the encroachment of woody plant species which would shade out grassland plants. Much of the research on cattle grazing and butterflies has taken place in semi-natural grasslands in Europe. There is comparatively little work in the US, and most of the US-based studies have focused on Midwestern prairies.
My work aims to understand whether there is a potential for cattle grazing to contribute to prairie butterfly habitat in the South Puget Sound. I have two main projects related to cows and butterflies.
The first project used butterfly behavior as an index of habitat quality under different types of management. The first type was “conventional” grazing, which I defined as cows having access to the whole pasture throughout the season. The second type was “conservation” grazing, which I defined as rotational grazing, where cows are moved around to give the plant community more time to recover between grazing periods, and a spring rest period, where cows are kept off the pasture in early spring when many plants (and caterpillars) are more vulnerable to grazing. There were also two native prairie sites, Johnson Prairie on Joint Base Lewis McCord, and West Rocky Prairie which is owned by WDFW. I followed adult butterflies of two common native species (silvery blues, Glaucopsyche lygdamus; and ochre ringlets, Coenonympha tullia eunomia) to see how they behaved under the different management types. Anecdotally, I found that as long as the host plant and nectar resources that they needed were present, the butterflies seemed to use them regardless of grazing management. This tells me that there is a potential for conservation grazing to contribute to butterfly habitat in the landscape.
My second project, which I am working on this summer, is comparing adult butterfly habitat preference with larval performance. I am working on a ranch with two different grazing treatments that are similar to the conventional and conservation grazing types described above. I release butterflies along the border between treatments to see if they have a preference for one type of habitat over another. I will also place caterpillars in the treatments and compare their residence times (how many days we were able to observe them), which is a proxy for survival. I am currently about halfway through data collection for this project, so stay tuned!
While more analysis is needed before I say for sure, conservation grazing may help maintain or improve habitat for butterflies by increasing nectar and host plant availability, which butterflies seem to recognize as good habitat.