Uncompahgre Fritillary Butterfly

Boloria acrocnema

Description

The Uncompahgre fritillary is a small butterfly with a 1-in (2.5-cm) wingspan. The upper wings are rusty brown, crisscrossed with black bars. The forewing is light ocher below, and the hind wing has a jagged white bar separating the crimson-brown inner half from the purple-gray outer half. Females are generally lighter above than males. The body has a rusty brown thorax and a brownish-black abdomen. The species is considered by some to be Boloria improba ssp. acrocnema, a subspecies of the dingy arctic fritillary. It has also been classified as Clossiana acrocnema.

Behavior

Adults feed on a variety of alpine flowers. Females lay eggs on snow willow (Salix reticulata ssp. nivalis ), which is the larval food plant.

Researchers believe that the Uncompahgre fritillary has a biennial life cycle. Eggs laid in the summer become caterpillars the following summer and mature into adult butterflies during the third summer. There are thus separate even-and odd-year populations within the same habitat area.

This butterfly is relatively sedentary and a weak flyer that stays close to the ground, making it an easy target for collectors.

Habitat

The Uncompahgre fritillary inhabits cool, moist mountain slopes above 13,200 ft (4,020 m). It is always associated with patches of snow willow, which provide larval food and cover.

Distribution

This species has the smallest range of any North American butterfly. It was discovered on Uncompahgre Peak in Hinsdale County, Colorado, in 1978. Another site was discovered in 1982 on land managed by the U. S. Bureau of Land Management (BLM). In 1988 a few individuals were captured at two additional sites. The total known range includes the San Juan Mountains and southern Sawatch Range in Gunnison, Hinsdale, and possibly Chaffee Counties in southwestern Colorado.

Since this species was discovered only recently, its current range is the same as its historic range, and it is not known whether the species was formerly more widespread. The original Uncompahgre Peak population is in the Big Blue Wilderness in the Uncompahgre National Forest. The second population is in a wilderness study area administered by the BLM. The two additional sites where some individuals were found in 1988 require more study to determine whether they support viable populations. Reports that four additional colonies have been discovered are as yet unconfirmed.

Surveys conducted in the 1970s and 1980s indicated that populations at the major colonies were on the decline. The even-year brood at Uncompahgre Peak had declined from about 800 in 1978 to about 200 in 1988. The population at the BLM site had declined from more than 1,000 in 1984 to about 500 in 1988. The odd-year brood at Uncompahgre Peak, which had been documented in the past, may be extinct, and the status of the odd-year brood at the BLM site was unclear. The U. S. Fish and Wildlife Service estimated the total population to be about 1,000.

Threats

The overwhelming threat to the Uncompahgre fritillary is butterfly collectors. As one of the few North American species discovered in the twentieth century, it is in great demand by collectors, and individual specimens are often sold for more than US$100. Although collecting has been banned by the U. S. Forest Service (USFS) in the Uncompahgre Peak area, some collection apparently continues. There has been no ban on collecting at the BLM site. Now that the Uncompahgre fritillary has been listed as endangered, collecting the species is illegal and can be prosecuted by federal authorities.

The small size of the known population and the need for a cool, wet habitat also threaten the long-term viability of the Uncompahgre fritillary. Besides the pressures of collecting, the species is vulnerable to such unpredictable natural events as prolonged drought or climatic change.

Conservation and Recovery

In 1984 the USFS and the BLM came to an agreement on conservation of the Uncompahgre fritillary. Besides banning collecting on USFS land, trails near the BLM site were rerouted to reduce recreational traffic in the habitat area.

Contact

U. S. Fish and Wildlife Service
Regional Office, Division of Endangered Species
P.O. Box 25486
Denver Federal Center
Denver, Colorado 80225
http://www.r6.fws.gov/

References

Brussard, P. F., and H. Britten. 1989. "Final Report on the Uncompahgre Fritillary (Boloria acrocnema )." Report prepared for the U. S. Forest Service, U. S. Bureau of Land Management, and U. S. Fish and Wildlife Service. Montana State University, Bozeman.

Gall, L. E. 1984. "Population Structure and Recommendations for Conservation of the Narrowly Endemic Alpine Butterfly, Boloria acrocnema (Lepidoptera: Nymphalidae). Biological Conservation 28: 111-138.

U. S. Forest Service and U. S. Bureau of Land Management. 1984. "Interagency Agreement and Species Management Perspective for Mt. Uncompahgre Fritillary Butterfly (Boloria acrocnema )." U. S. Forest Service and U. S. Bureau of Land Management, Gunnison, Colorado.