The Nature Conservancy and the Washington State Department of Fish and Wildlife (WDFW) partnered in an attempt to study and protect endangered butterflies of the southern Puget Sound prairies. The purpose of the study was to gather information so that prairie restoration efforts could improve the welfare of these butterflies. As has been described in previous issues of G’Num, WBA aided these efforts by surveying for butterflies at Fort Lewis. Ann Potter and David Hays, who lead the project for WDFW, described the study at the November WBA meeting.

In 1998-1999, Potter, Hays and other researchers from WDFW collected information on the feeding behavior and habitat selection of four rare butterflies: the mardon skipper (polites mardon), Puget blue (a subspecies of Boisduval blue, Icaricia icarioides blackmorei), Whulge or taylor’s checkerspot (a subspecies of edith’s checkerspot, Euphydryas editha taylori), and the valley silverspot (Speyeria zerene bremnerii). The sites chosen for the study were the Scatter Creek Wildlife Area in Thurston County and Fort Lewis.

The populations of all these species appear to be declining but the reasons for the decline are not understood. It is likely that reduction of their habitat makes a significant contribution to their decline. According to Potter and Hays, only three percent of an estimated 150,000 acres of grasslands remain in the south Puget Sound region. All four species were proposed for listing as threatened or endangered by WDFW in 1989. The mardon skipper was designated a state endangered species in 1999, and also became a candidate for federal endangered species listing in 1999.

The purpose of the study was to gather information needed for management of the butterflies’ habitat. The State and other organizations were restoring habitats but more information was necessary to ensure that the butterflies’ needs were met. WDFW studied the plants the butterflies used for nectar, the characteristics of the vegetation in the nectars areas and the amount of Scotch broom in the nectar areas.

The study focused on the question of which nectar plants these species prefer. The researchers selected sample areas believed to have high populations of each species. During the peak flight periods, the researchers walked transects in the sample areas. When a researcher saw a butterfly, they observed and recorded its behavior for ten minutes or until they could no longer see it. The also kept records of what nectar plants were available so the frequency of use of nectar plants could be compared to their availability of plants.

The study showed that the Puget blues preferred unopened buds of sickle-keeled lupine, Lupinis albicaulis, possibly feeding on aphid honeydew. The mardon skipper nectared almost exclusively on Viola adunca in 1998 and showed a strong preference for it and common vetch (Vicia sativa) in 1999. The valley silverspot nectared only on Canada thistle in 1998 (Cirsium arvense), but in 1999 also used showy fleabane (Erigeron speciosus). Insufficient data was available about checkerspots’ preferences, but the study suggested they preferred common camas (Camassia quamash)

It was interesting to note that the preferences of two species were different in the two years of the study. It is believed this indicates an ability on the part of these species to take advantage of a variety of food sources, in response to differences in availability of plants. The study also showed that all four species chose areas with relatively short Scotch broom cover.

Except for Puget blue, the timing of the emergence of adult butterflies and the plants’ nectar production did not always coincide, so the butterflies’ choice of nectar plants varied year by year. The study recommended that prairie restoration and management efforts focus on areas with abundant nectar species, especially at the edges of forest and grassland edges. Control of Scotch broom was determined to be essential. Because Canada thistle is a nectar source later in the season, after other sources have disappeared, control of it should be limited even though it’s classified as a noxious weed.

The study concluded that availability of late-season nectar may limit populations.

While the study provided valuable information about the preferences of the species, the information is still incomplete. The study covered only the peak flight period; we don’t know much about their habits during the other times of the year. The study only looked at adult feeding behavior; it didn’t consider larvae or ovipositing.

G’num2004Vol5No1