Laguna Mountains Skipper

Pyrgus ruralis lagunae

Description

The Pyrgus ruralis lagunae, (Laguna Mountains skipper) is a small butterfly in the skipper family (Hesperiidae). It has a wingspan of about 1 in (2.5 cm) and is distinguished from the rural skipper (P. ruralis ruralis ) by extensive white wing markings that give adults, particularly males, an overall appearance of white rather than mostly black, and by the banding patterns on the hind wings. The Laguna Mountains skipper is found in montane meadow habitats.

The Laguna Mountains skipper is one of two recognized subspecies of the rural skipper, P. ruralis lagunae, based upon population isolation and color differentiation. The Laguna Mountains skipper is restricted to the Laguna Mountains and Mount Palomar in San Diego County. The other subspecies of the rural skipper (P. ruralis ruralis ) ranges from the mountains of British Columbia and Alberta, Canada, south to the coast ranges and Sierra Nevada of central California, as well as Nevada, Utah, and northern Colorado and has darker wings than the Laguna Mountains skipper.

Three other species in the genus Pyrgus occur in San Diego County: the common checkered skipper (P. communis ), the small checkered skipper (P. scriptura ), and the western checkered skipper (P. albescens ). The Laguna Mountains skipper can be distinguished from all three of these species by the whitish appearance of the adults and the use of a single larval host plant, Horkelia clevelandii, Cleveland's horkelia, in the rose family. In addition, the western checkered skipper and southern California populations of the small checkered skipper are restricted to desert areas.

Behavior

The Laguna Mountains skipper apparently produces two generations per year. The adult flight season occurs from April to May with a second smaller flight in late June to late July. The Laguna Mountains skipper may have evolved a unique mechanism for coping with the low daytime temperatures it encounters during its spring flight, which is unusually early for butterflies in the Laguna Mountains. It is assumed that the life history of the Laguna Mountains skipper is similar to that of Pyrgus ruralis ruralis, which maintains a state of suspended activity as a full grown larva and lives 10-20 days in the adult stage.

Adults of the species feed on flower nectar.

Habitat

Cleveland's horkelia, the larval host plant of the Laguna Mountains skipper, occurs in meadows, under pines, and on granite in the Laguna, Cuyamaca, Palomar, and San Jacinto Mountains of southwestern California and northwestern Baja California, Mexico, from 4,000-8,000 ft (1,200-2,400 m) in elevation. Although the distribution of a butterfly is primarily defined by the presence of its larval host plant, the butterfly may be further restricted by other physiological or ecological constraints. The Laguna Mountains skipper is currently found in a few open meadows of yellow pine forest between 4,000-6,000 ft (1,200-1,800) in elevation.

Distribution

Historically, this skipper may have occurred throughout the higher elevations of San Diego County. There were at least six populations of this taxon in the Laguna Mountains in the 1950s and 1960s; however, current information indicates only one extant population. Until its rediscovery in 1983 and subsequent sightings in 1986 and 1995, this skipper had not been seen in the Laguna Mountains since 1972.

Historically, the Mount Palomar populations were small compared to the populations in the Laguna Mountains. Only five specimens have been collected from Mount Palomar in this century. Prior to specimens collected in 1991 and the additional populations found in 1994, the last known sightings from Mount Palomar were from 1980 and, prior to that, from 1939.

The Laguna Mountains skipper population in the Laguna Mountains in San Diego County was not seen during a relatively extensive survey in 1994 but was seen in 1995. Prior to that observation, it was last seen in the Laguna Mountains in 1986 occupying a small area along a fence in a U.S. Forest Service campground. The Laguna Mountains population was estimated to consist of fewer than 100 individuals. The Laguna Mountains skipper is currently found at four sites in the Mount Palomar region of San Diego County. The largest of the Mount Palomar populations is estimated to comprise 240 individuals.

Threats

The Laguna Mountain skipper is threatened by loss and degradation and fragmentation of habitat due to grazing, urban development, and fire management practices; over-collection and other human disturbance; and naturally occurring events such as fire or weather extremes.

If there were greater numbers of individuals and more populations, the Laguna Mountains skipper might be able to tolerate certain levels and timing of livestock grazing. However, given the low numbers of this butterfly, any impacts to its habitat would be significant. The grizzled skipper (Pyrgus malvae ) in England is able to tolerate grazing at a highly managed level. The rare Dakota skipper (Hesperia dacotae ) is sensitive to even light grazing. Some species of butterflies have habitat requirements that need a managed grazing scheme whereas others have habitat that recovers with reduced grazing. However, previous studies indicate that the use of grazing as a management tool for butterflies must be done carefully and at low intensities. A grazing plan for management of the Laguna Mountains skipper has yet to be developed.

Conservation and Recovery

Some protection is afforded to the Laguna Mountains skipper on U.S. Forest Service land. Considering the small population size and extremely limited distribution of the Laguna Mountains skipper, this protection is insufficient to conserve the butterfly.

Fire may be a necessary component for the maintenance of Laguna Mountains skipper habitat. The diversity of montane meadow habitats may be fire-dependent, including the skipper's larval host plant. Historically, the skipper may have experienced local extirpations and recolonizations following local fire events. However, the present discontinuity and low population numbers would not enable the Laguna Mountains skipper to tolerate local extirpations due to fire.

Contact

U. S. Fish and Wildlife Service
Regional Office, Division of Endangered Species
Eastside Federal Building
911 N. E. 11th Ave.
Portland, Oregon 97232-4181
Telephone: (503) 231-6121
http://pacific.fws.gov/

References

Levy, J. N. 1994. "Status of the Laguna MountainsSkipper Butterfly (Pyrgus ruralis lagunae J. Scott).Biological Survey and Analysis prepared for the Forest Service, United States Department of Agriculture.

Northern Prairie Wildlife Research Center. "Butter-flies of Montana." http://www.npwrc.usgs.gov/resource/distr/lepid/bflyusa/mt/659.htm (29 June 2000).

Scott, J. A. 1986. The Butterflies of North America. Stanford University Press, Stanford, California.