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ARCATA FWO: Taking Flight — Summer is Survey Season for the Oregon Silverspot Butterfly
California-Nevada Offices , September 15, 2016
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Newly emerged Oregon silverspot butterfly nectaring on yarrow (Achillea millefolium) near a restoration site at the Lake Earl Wildlife Area in Crescent City, California
Newly emerged Oregon silverspot butterfly nectaring on yarrow (Achillea millefolium) near a restoration site at the Lake Earl Wildlife Area in Crescent City, California - Photo Credit: K. Mierzwa/USFWS
Surveying for Oregon silverspot butterfly along an established transect during a recent surveyor refresher training at Del Norte Habitat Conservation Area (July 2016). Those in picture are current orr former Service staff of the Arcata Fish and Wildlife Office: Ecologist Susie Tharratt and Fish and Wildlife Biologist Lynn Roberts, walking ahead of Gary Falxa (retired).
Surveying for Oregon silverspot butterfly along an established transect during a recent surveyor refresher training at Del Norte Habitat Conservation Area (July 2016). Those in picture are current orr former Service staff of the Arcata Fish and Wildlife Office: Ecologist Susie Tharratt and Fish and Wildlife Biologist Lynn Roberts, walking ahead of Gary Falxa (retired). - Photo Credit: Cristina Bauss/USFWS
An Oregon silverspot butterfly alighting on Erigeron sp. in Crescent City, California. This butterfly is listed as Threatened under the Endangered Species Act of 1973. Note the silver spots on the underside of its wings, lending to its common name.
An Oregon silverspot butterfly alighting on Erigeron sp. in Crescent City, California. This butterfly is listed as Threatened under the Endangered Species Act of 1973. Note the silver spots on the underside of its wings, lending to its common name. - Photo Credit: Chris Damiani/USFWS
Environmental Scientist Frank Kemp (California Department of Fish and Wildlife) surveying for Oregon silverspot butterfly at a northern transect within the Del Norte Habitat Conservation Area, in Crescent City, California. This photo exhibits some of the typical habitat where the species is found within the Tolowa Dunes State Park.
Environmental Scientist Frank Kemp (California Department of Fish and Wildlife) surveying for Oregon silverspot butterfly at a northern transect within the Del Norte Habitat Conservation Area, in Crescent City, California. This photo exhibits some of the typical habitat where the species is found within the Tolowa Dunes State Park. - Photo Credit: Susie Tharratt/USFWS
Close-up of  Viola adunca, or early blue violet (a member of the violet family), the Oregon silverspot butterfly's larval host plant. Caterpillars of the Oregon silverspot butterfly feed primarily on early blue violets. Violet abundance and native nectar sources have declined at all Oregon silverspot butterfly habitat areas due primarily to competition from non-native vegetation.
Close-up of Viola adunca, or early blue violet (a member of the violet family), the Oregon silverspot butterfly's larval host plant. Caterpillars of the Oregon silverspot butterfly feed primarily on early blue violets. Violet abundance and native nectar sources have declined at all Oregon silverspot butterfly habitat areas due primarily to competition from non-native vegetation. - Photo Credit: Gary Falxa/USFWS

By Susie Tharratt and Cristina Bauss

The only known population of Oregon silverspot butterflies (Speyeria zerene hippolyta, or silverspot butterfly) in California occurs along salt-spray meadow habitats adjacent to a coastal dune complex near Lake Earl, the largest coastal lagoon in the state, situated in Del Norte County. Each summer from early July until mid-September, one just might stumble upon the weekly field survey—or more accurately, the field surveyors—who take part in rangewide population monitoring efforts for this threatened butterfly. Surveys coincide with the time of adult emergence, or flight period, and are meant to inform general population trends on an annual basis. Data collected at the Del Norte Habitat Conservation Area, one of six  habitat conservation areas identified in the 2001 Revised Recovery Plan for the Oregon Silverspot Butterfly (Service 2001), contribute to a larger population monitoring program implemented by the U.S. Fish and Wildlife Service (Service), led by the Newport Field Office of the Oregon Fish and Wildlife Office. 

The silverspot butterfly is a medium-sized (wingspan of approximately 2.2 inches or 5.5 cm) member of the brush-footed family (Nymphalidae). It is bright orange and brown with black veins and spots on the upper wing surface, and a yellowish submarginal band and bright metallic silver spots on the underside wing surface; these spots, in part, contribute to its common name. One of many subspecies of the zerene fritillary, the Oregon silverspot butterfly was historically distributed along the Washington and Oregon coasts, from Westport in Grays Harbor County, Washington, south to Heceta Head in Lane County, Oregon, with a disjunct population located north of Crescent City in Del Norte County, California. Today only six small populations persist:  five in Oregon (at Clatsop Plains, Mount Hebo, Cascade Head, Bray Point, and Rock Creek-Big Creek) and one in far northern California, within the state’s Lake Earl Wildlife Area (LEWA) and Tolowa Dunes State Park areas. The California population was not discovered until after the subspecies was listed as threatened in 1980.   

Presumably cued each summer by the arrival of appropriate conditions, caterpillars typically emerge from their pupae (called adult emergence) beginning in July and extending into September. Males typically appear several weeks before most females emerge. This is when a small cadre of dedicated resource biologists from the Service’s Arcata Fish and Wildlife Office (AFWO), California Department of Fish and Wildlife, National Park Service, and California State Parks sets off to count silverspot butterflies, in renewed optimism of determining how the California population is recovering.   

In its eleventh year, the California monitoring effort was established in 2005 by AFWO botanist David Imper and biologist Gary Falxa, both now retired. Data collected in California dovetail into a similar monitoring program established by the Nature Conservancy in 1990 in Oregon. This monitoring effort provides the Service with invaluable information on the status of the butterfly rangewide, allowing managers to identify and ameliorate threats, track restoration progress and identify new areas for management action, inform augmentation efforts, and estimate an annual index of abundance value (Index), which provides a relative population measure from year to year—although seemingly, two years are never alike among all the monitored sites! With each passing year, new data and findings present managers with both challenges and opportunities for conservation and restoration practices. 

This year (2016) has been a perfect example of this fact. With California in a fifth straight year of drought-like conditions and with notable changes in timing of precipitation and frequency of low-lying fog, changing environmental factors are a cause for worry at the Del Norte Habitat Conservation Area. Populations are most at risk when unfavorable weather conditions occur in consecutive years. At the southern end of their distribution, silverspot butterflies may well be struggling to adapt to regional-level climatic shifts along with habitat changes occurring within a human-altered landscape. Early reports are survey numbers for this population this year are lower than expected, and the overall Index may be trending downwards. 

But on this late-July day, as Gary Falxa assisted new trainees in the finer points of population surveying, everyone appeared enthused and hopeful while reviewing detailed protocols codifying the times (between 1000 and 1400 hours) and prevailing environmental conditions (including temperature, percent overcast, and wind speeds) under which surveys can be conducted. In addition to highlighting nuances such as scanning arc and walking speed, this periodic training event allows surveyors to “standardize” techniques to ensure reliable year-to-year population-index estimates. During a recent training, the sight of multiple people seemingly engaged in repetitive, almost robotic action—walking very slowly while swiveling their heads even more slowly—was intriguing enough to evoke questions from more than one passing motorist. 

Surveyors work in pairs, each trainee with an individual trainer, on fifteen transects. A few are in Tolowa Dunes State Park; the remainder are within the LEWA, or along public parcels newly acquired from the former Pacific Shores subdivision. Transects are “fixed” (i.e., revisited and the same year-to-year) along mapped areas that in 1990 had higher concentrations of the small, perennial early blue violet (Viola adunca), the butterfly’s primary food resource when it is in its larval (caterpillar) phase. Within these “suitable” habitat areas transects are scattered, each between 200 and 500 meters in length. Transects are surveyed the same way each year, and each is demarcated every 50 meters to help ensure a fixed level of effort during protocol-level surveys. During the July surveyor training, these 50-meter marks allowed for natural pauses where trainers and trainees stopped to record sightings, standardize and fine-tune their techniques, and verify non-targeted butterfly identifications or observations. 

The Oregon silverspot was once much more abundant along coastal habitats in the Pacific Northwest. However, higher-quality grasslands in terms of associated vegetation type (dune, montane, or coastal terrace), size, and proximity to adjacent occupied habitat that allows for dispersal and connectivity is becoming increasingly reduced and fragmented. Habitat loss and degradation continue to threaten and isolate existing populations of silverspot. Furthermore, early blue violets—once endemic to coastal terraces and headland “salt-spray” meadows and stabilized dunes (seen in five of the six known sites in Oregon and California) and montane grasslands such as those on Mount Hebo in Oregon (the sixth site)—are becoming less prevalent. This is partly due to changes in plant assemblages and soil conditions following conversion from early-successional native-plant communities into later-successional habitats comprised largely of non-natives and conifers. In the past, these meadow habitats were maintained by periodic wildfire and wildlife grazing; today they are quickly being lost to fire suppression activities, accelerated development and fragmentation, and in some areas, excessive use by off-road vehicles or over-grazing by domestic animals. 

Some restorative measures, such as controlled burning or use of limited grazing treatments, can be applied on larger parcels of public land to restore and maintain processes that favor native species and reset the early-successional composition of habitat types. However, most of the butterfly’s known population occurs on smaller, patch-sized fragments of habitat, a checkerboard of public and private property that poses challenges for large-scale restoration efforts and may inhibit reestablishment of natural colonization processes. In addition, when managing for endangered and threatened species the Service and others must carefully weigh the pros and cons of invasive species plant removal. For instance, tansy ragwort (Senecio jacobaea) is not native to North America—but because it is observed as a frequently-used plant resource by silverspot butterfly for nectaring at the Del Norte Habitat Conservation Area, it has not been targeted for removal. In similar fashion, native species augmentations, or plantings, pose their own management challenges; planting native Viola requires careful consideration of seed source. Furthermore, emerging or exacerbating risks to the species—for example the alteration in the timing of adult butterfly emergence with locating appropriate food and nectar resources (phenology), for example—within this fragmented, patchwork landscape may also drive future conservation questions and actions. As the AFWO’s Ecologist Susie Tharratt indicated, once habitat features and conditions are missing in suitable quantity and quality from the landscape “long-term persistence of this butterfly is less likely.” Tharratt has taken over from Falxa in leading the monitoring effort for the AFWO.

Will the Oregon silverspot go the way of the Lotis blue butterfly (Lycaeides argyrognomon lotis), last seen in Mendocino County in 1983? Not if efforts to save it continue to experience some degree of success. In response to a serious population decline in the 1990s, in 1998 the Service partnered with the Oregon Zoo in Portland and the Woodland Park Zoo in Seattle to develop a population supplementation program. Each year about 2,000 zoo-reared Oregon silverspot butterflies are released on the Oregon coast. The Nature Conservancy is working with the U.S. Forest Service on habitat restoration, using controlled burns in an attempt to re-establish early blue violets in meadows that had given way to brush and forest. There is even an award-winning beer, Silverspot IPA, inspired by the butterfly; brewed by Pelican Pub & Brewery in Tillamook, a portion of the proceeds is earmarked for conservation efforts. But recovery takes time, and time alone may not be enough. 

In Del Norte County, there was a little good news on the day Gary Falxa volunteered to help new trainees. All eight surveyors had recorded at least one silverspot butterfly, and some had seen three or four. 

 

 
Susie Tharratt is an ecologist for the Endangered Species Program at the Arcata Fish and Wildlife Office in Arcata, Calif.

Cristina Bauss is a recent graduate of the Humboldt State University Geography Program, and is on contract to the Arcata Field Office.


Contact Info: Susie Tharratt, 707-825-5117, susie_tharratt@fws.gov
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