Lupinus sulphureus spp. kincaidii (Kincaid’s lupine) and Icaricia icarioides fenderi (Fender’s blue butterfly) in the West Eugene Wetlands: Population monitoring, reintroduction success, and an evaluation of experimental treatments

This report documents research conducted on Kincaid’s lupine (Lupinus sulphureus ssp. kincaidii), a threatened species in the legume family. Kincaid’s lupine serves as an obligate larval host plant for the endangered Fender’s blue butterfly (Icaricia icarioides fenderi). Both species are endemic to western prairies. The specific objectives of this project are to 1) describe trends of Kincaid’s lupine and Fender’s blue butterfly eggs at sites managed by the Eugene District Bureau of Land Management in the West Eugene Wetlands (in 2010 Fir Butte and Oxbow West; previous monitoring efforts included Isabelle, Turtle Swale, and Dragonfly Bend), 2) evaluate mowing and burning as management treatments for reducing invasive weeds and enhancing Kincaid’s lupine and Fender’s blue butterfly populations, and 3) evaluate estimates of lupine foliar cover as an alternative to time-consuming leaf counts.

1. Populations of Kincaid’s lupine in the WEW increased in abundance in 2010. Egg counts for Fender’s blue butterfly continued to be relatively low at Oxbow West, and increased at Fir Butte from 2009.a. Fir Butte was the largest population monitored in this area, with approximately 133,112 inflorescences and a total foliar cover of 2,605 m2. This remains the highest value for the cover of lupine since monitoring began in 1998, and is a substantial increase from 2009. The number of inflorescences in 2010 was higher than any previous year. The estimated number of Fender’s blue butterfly eggs was the highest ever with approximately 17,950.b. The lupine population at Oxbow West plateaued in 2008, decreased in 2009 and has slightly rebounded in 2010. The lupine population still covers about 75 m2. We counted 4,899 inflorescences, the fourth highest number recorded since monitoring began in 1999. We estimated that there were only 35 Fender’s blue butterfly eggs, a precipitous decline from previous estimates.
2. From 1998 through 2008, we evaluated the effects of mowing annually, every two years, and prescribed fire. While all management treatments benefited lupine cover and decreased the cover of Rubus armeniacus, the greatest benefits were from burning, followed by frequent (at least once per year) mowing. The number of butterfly eggs was unaffected by treatments.
3. Estimating foliar cover is an acceptable alternative to counting leaves of Kincaid’s lupine when combined with flower stem counts, especially if the objective is to measure trends in lupine abundance. Lupine leaf density is positively correlated with foliar cover, and this relationship is strongest in habitats with full sun (such as most Willamette Valley sites). Regional differences in this relationship make direct comparisons of lupine cover across sites unreliable in some cases because lupine leaf density varies with the amount of sunlight reaching the habitat.