Wildlife fender-bender: Recovery plan for the endangered Fender's Blue Butterfly

by Alexa Addleman

Male (left) and female varieties of Fender's Blue Butterfly (Oregon Fish and Wildlife Office)

Land of the butterflies

Lupinas kinkaidii, host for FBB larvae 
(Bureau of Land Management) 

(Oregon Fish and Wildlife Office)

Nestled in the quiet Willamette Valley of Central Oregon are sweeping prairie lands that have been home to abundant wildlife for centuries. One species, the Fender's Blue Butterfly, is endemic to this area, and now finds itself in peril. It was first found in 1929, and seen scarcely until 1937 before disappearing for 50 years due to uncertainty about its host plant (Hammond and Wilson, 1992). It was rediscovered again in 1989, and is associated with a perennial lupine species lupinas kincaidii. The butterfly occurs on upland prairies characterized by native bunch grasses. On January 25, 2000, it was listed as endangered without critical habitat. 

Behind the Blue: Ecology of the Fender's Blue Butterfly

Larvae on a lupine
(Institute for Wildlife Studies)

A female Fender's Blue Butterfly (Matthew Benotsch/TNC)

Though their whole life cycle occurs over the course of nearly a year, adult Fender’s Blue Butterflies live 10 to 15 days, and rarely travel further than a mile over their lifespan (Schultz, 1998). Their wingspan is only one inch, about the size of your thumb. Males are iridescent blue and females are reddish-brown, both with cream colored undersides. Females lay around 350 eggs in their lifetime, but usually no more than a few survive to adulthood. They lay their eggs on perennial lupines during May and June, and larvae remain in an extended diapause (state of dormancy) for nearly a year before spending two weeks in the pupal stage and emerging as adult butterflies (Ballmer and Pratt, 1998). The larvae have glands that secrete a sweet solution that ants like, making the ants tend to the larvae and protect them from predators. 

From sources to sinks, real quick

(Natural Resources Conservation Service)

The prairies of Willamette Valley have been hit by degradation and fragmentation, causing habitat loss for the butterflies as well as their host plants. These habitats have also been invaded by tall non-native grasses that limit the ability of the butterfly to find a host plant (Severns, 2008). The butterflies exist in stepping-stone metapopulations, or small patch habitats that are connected sequentially, and fragmentation of their habitat has cut off some patches from others. Few of these populations occur on protected lands, while the majority are found on private lands that aren’t and can’t be managed by the Oregon government. Invasive species are also a huge threat to the butterfly - the Oregon Department of Agriculture established a Gypsy Moth eradication program that sprays a chemical BTK to kill them, but it’s lethal to all butterflies and moths. Its fumes can travel over two miles from the point of application, killing Fender’s Blue Butterfly larvae that live nearby. 

Hope for Fender's

3,300 feet of 'wildlife-friendly fence' was built on two sides of the property to keep nearby cattle from wandering onto the Fender's Blue butterfly conservation site near Philomath (Tim Browning, TB Irrigation)

Butterflies being relocated and released (Mike McInally)

After many studies on the remaining butterfly populations, it was decided that the butterfly could be down listed or delisted based on minimum population, not average population, and based on the networks inside recovery zones. So far, populations have responded positively to habitat restoration. Mowing, burning and removal of weeds have resulted in increasing populations. A study showed that the best long-term population growth can be found through burning one-third of the habitat each year (Schultz and Crone, 1998). Burning some sink patches has killed all the larvae there, but females from nearby source patches recolonized them the following year, and eggs were 10 times more abundant than control patches left untouched. Researchers also experimented with capturing butterflies and using Puget Blue Butterflies as a surrogate to hatch eggs, but most offspring died and survivors had smaller wings and body length than original FBB. A better solution is to transfer late-stage larvae from existing populations to reintroduction sites. Most important in the recovery plan are the sites, with specific characteristics that make for delisting. Recovery sites require a minimum growth rate of 1.55 and have to be at three independent sites in each of the three zones in the butterfly’s historical range. Each recovery site must have either two networks or one network and two independent populations.

Characteristics of a recovery site that would, if maintained, allow for the down listing of FBB (Recovery Plan)