Periodic Status Review for the Mardon Skipper (2023)

The mardon skipper (Polites mardon) is a small tawny-orange butterfly with a stout, hairy body found in five disjunct regions in Washington, Oregon, and California: 1) south Puget Sound, 2) southern Washington Cascades, 3) southern Oregon Cascades, 4) southern Oregon coast, and 5) coastal northern California. The mardon skipper is estimated to occupy 165 sites that represent approximately 66 populations rangewide. “Sites” refers to the specific locations with documented species presence, and “populations” represent local clusters of sites that are assumed to function as a local population.

In Washington, most of the known sites are in the southern Washington Cascades with a few sites located in the south Puget Sound prairies in Thurston and Pierce Counties. It has been state-listed as endangered since 1998 and was a federal candidate for Endangered Species Act listing from 1999-2012. In 1999, only nine sites were known, six from the southern Washington Cascades, and three from the south Puget Sound prairies. However, after an extensive survey effort from 2000-2011, approximately 117 sites and approximately 49 mardon skipper populations were documented in Washington State, with nearly all found in the southern Washington Cascade region. Therefore, the U.S. Fish and Wildlife Service determined that rangewide listing was not warranted.

Mardon skippers were once more broadly distributed on the south Puget Sound prairies. Urban development, forest encroachment, introduction of invasive species, and land conversion to agriculture have reduced the south Puget Sound region prairies and available mardon skipper habitat to a fraction of their previous extent. Today, mardon skippers remain on only three sites: the Artillery Impact Area of Joint Base Lewis-McChord, and the North and South Units of Scatter Creek Wildlife Area (WLA). The numbers of mardon skippers at the Scatter Creek WLA have declined significantly since 2008-2009, from hundreds to only a few individuals documented in 2021. In 2022 and 2023, surveys conducted at both units of Scatter Creek WLA detected no mardon skippers during their flight period. Further monitoring over the next few years will determine if the Scatter Creek WLA populations are extirpated. The dramatic decline in mardon skipper numbers in the south Puget Sound prairies shows that mardon skipper numbers are critically low compared to what has been documented over the last two decades.

Mardon skippers have narrow habitat requirements, though specific host and nectar plants appear to vary by region. Generally, mardon skippers require open grassland and meadows dominated by short-statured grasses or sedges and forbs including larval host plants (grasses and sedges), and nectar sources for adults. South Puget Sound populations are found on prairies with glacial outwash soils dominated by native grasses such as Roemer’s fescue (Festuca roemeri) interspersed with early blue violet (Viola adunca) and other nectar plants.

Mardon skipper populations are affected by several factors including conifer/shrub encroachment, invasive grasses, grazing by domestic livestock, off-road vehicle use, prescribed and natural fire, recreation, pesticides, issues related to small population size, and climate change-driven factors (e.g., drought, shifts in flowering resource phenology and hydraulic periods). Mardon skippers have limited dispersal abilities. Barriers and distance between sites likely limit recolonization and colonization of new sites. Many populations are small and at risk of extirpation.

Although many additional mardon skipper sites and populations were documented in the southern Washington Cascades since state listing, the south Puget Sound prairie sites and populations have seriously declined, and the skipper’s status is precarious. Washington defines “Endangered” to mean any wildlife species native to the state that is seriously threatened with extinction throughout all or a significant portion of its range. Given that the south Puget Sound populations represent a significant portion of its range and the threat of extinction in these few remaining sites is high, it is recommended that the mardon skipper remain listed as endangered in Washington.