Fender’s Blue Butterfly in 2020

By Carolyn Menke

January 2021

Every year poses a unique challenge when trying to complete sunshine-dependent butterfly surveys in the Pacific Northwest, but 2020 definitely stands out.  The initial surge of the COVID-19 pandemic began just before the onset of the monitoring season for one of the endangered butterflies of Oregon’s Willamette Valley, Fender’s blue (Icaricia icarioides fenderi). Fender’s blue surveys were, for the most part, able to occur as normal, since the survey method is inherently socially distanced and in line with COVID-19 safety protocols.  We adapted the annual training into an online format and our dedicated team worked hard to get to as many sites as possible when weather conditions were favorable – just a few were closed for access.  We’re so grateful for the logistical support of the Willamette Valley conservation and land management community!

Since 2016, IAE has coordinated annual surveys for the endangered Fender’s blue across its range in Oregon’s Willamette Valley. Fender’s blue butterfly was listed as an endangered species in 2000 primarily because of its extreme rarity due to upland and wet prairie habitat loss and fragmentation.  Sites in conservation with the butterfly have been monitored on a mostly annual basis for the last 10 years, and some, like those at Baskett Slough National Wildlife Refuge near Rickreall, Oregon, have been monitored regularly for almost 25 years.

The total number of butterflies can fluctuate substantially between years, which is likely driven by factors including weather and habitat conditions, along with survey method and technique.  Data suggest that roughly 3,000 Fender’s blue butterflies existed in 1993, which then fluctuated between approximately 6,300 and 1,750 individuals from 2000 to 2011. Since 2012, newly discovered populations, populations expanded through habitat restoration, and changes in sampling method may explain the substantial growth in numbers of Fender’s blue butterflies; as the overall estimated population in 2016 was a peak of nearly 29,000 butterflies.  Poor weather conditions in the winter and early spring of 2016-2017 contributed to a significant reduction in the estimated population size; declining by 50% to roughly 13,100 butterflies in 2017, and only recovering slightly to an estimated 13,700 butterflies in 2018. Increases across many sites with the butterfly contributed to a range-wide population estimate of nearly 24,500 butterflies in 2019.  2020 saw a decline of the overall population estimate to a total of 18,717 butterflies. Because we could not survey all sites, we suggest this is an underestimate of true population size for the year, but even if we roughly account for unsurveyed areas, the total population estimate for the year would still likely be less than 19,500 butterflies.

While this is still lower than what we saw in 2015, 2019, and the best-ever year of 2016, it is still the fourth highest population estimate on record for the species! This reinforces the benefits of habitat restoration to reduce invasive weeds and increase lupine host plants and native nectar plants. IAE is proud to report that with the support of Oregon Watershed Enhancement Board and numerous partners (including Benton County, Greenbelt Land Trust, Oregon Department of Transportation, US Fish and Wildlife Service, Bureau of Reclamation, Polk Soil and Water Conservation District, and Yamhill Soil and Water Conservation District) we are working on a project to expand the abundance and distribution of the threatened species Kincaid’s lupine (Lupinus oreganus) the host plant for Fender’s blue. Many of the sites receiving habitat restoration treatments and augmentation of lupine also host Fender’s blue. We look forward to tracking the benefits of this work for butterfly populations in the future.

IAE is grateful for funding provided by the U.S. Fish and Wildlife Service, and assistance from the Oregon Parks and Recreation Department. A huge thanks to all surveyors, including Christine Calhoun, Riley Duncan, Andrew Esterson, Greg Fitzpatrick, Paul Hammond, Amie Loop-Frison, Peter Moore, Gary Pearson, Dana Ross, Duncan Thomas and Rhiannon Cochrane. We are grateful to all public and private landowners who support surveys for Fender’s blue butterfly on their land. Our continued appreciation also goes to Tyler Hicks for his assistance with distance sampling analysis.