Open-File Report 2014–1044
This project provides baseline data of butterfly populations at two coastal prairie restoration sites in Louisiana, the Duralde Unit of Lacassine National Wildlife Refuge (hereafter, the Duralde site) and the Cajun Prairie Restoration Project in Eunice (hereafter, the Eunice site). In all, four distinct habitat types representing different planting methods were sampled. These data will be used to assess biodiversity and health of native grasslands and also provide a basis for adaptive management.
The goal of this project is to obtain baseline butterfly population data in grassland management areas. These data will provide a baseline to be compared with future sampling to better understand how management actions affect biodiversity and wildlife. This project will enhance management practices for benefitting grassland birds, identified as an important wildlife group in the comprehensive conservation plans for Lacassine and Sabine National Wildlife Refuges, La.
A 1,200-meter (m) transect was established at the Duralde site and divided into 14 segments, with each segment bisecting one of the four habitat types: diverse prairie, little bluestem (Schizachyrium scoparium) monoculture, brush-infested grassland, and tree-lined road. A 713-m perimeter walkway around the Eunice site was used as a transect with each of the four sides serving as transect segments. Transects were walked weekly from August 2012 to August 2013, and all butterflies encountered were identified to species. Individuals that were difficult to identify were netted for identification. Time spent per segment and weather conditions were also recorded. Vegetation associated with each transect segment was described by (1) dominant species, (2) structure, (3) nectar species, and (4) larval host species present.
Raw data were recorded in an Excel worksheet (available from the lead author).
Because of the low number of butterflies in the transect samples, analysis was limited to descriptive statistics. Summary statistics were made of butterfly flight times, butterfly species associations with vegetation type, and butterfly abundance by vegetation type.
At the Duralde site, 513 individuals from 19 species of butterflies were identified between August 14, 2012, and August 13, 2013. By contrast, 2,303 individuals from 32 species were identified at the Eunice site over the same time period.
The Duralde site is isolated in a matrix of agricultural fields with little or no nearby habitat and regular pesticide drift from adjacent rice and soybean fields. Surrounded by a mature urban setting, the Eunice site has adjacent garden, field, and forest habitat not subject to crop dusting spray. While refuge management cannot affect neighboring properties or pesticide use, habitat quality at the Duralde site could be improved as butterfly and wildlife habitat through specific planting and management actions.
Both nectar and larval host plants are less abundant at the Duralde site than at the Eunice site. Planting high-quality nectar species could increase species abundance at the Duralde site. Planting larval host plants of butterfly species typical of coastal prairie could increase both butterfly species richness and abundance.
Increasing frequency of prescribed burns could decrease thatch, which can suppress flowering of nectar plants. Burns conducted in late summer or early fall could increase forb flowering but could also have a negative effect on grassland birds. Annual patch burning could enhance the balance between invertebrates and grassland bird densities.
If continued beyond August 2014, annual transect counts would provide comparative data that can be used to assess biodiversity and health of native grasslands and provide a basis for adaptive management.
Dr. Malcolm Vidrine, Louisiana State University at Eunice.
Inkind support of salary, lab, and specimen storage facilities, insect collection equipment, camera, and vehicle provided by the U.S. Geological Survey.
Allain, Larry, and Vidrine, Malcolm, 2014, Progress report—Baseline monitoring of indicator species (butterflies) at tallgrass prairie restorations: U.S. Geological Survey Open-File Report 2014–1044, https://dx.doi.org/10.3133/ofr20141044.