The El Segundo blue butterfly (Euphilotes battoides ailyni) formerly extended over much of the 3,200 acre El Segundo Dunes of Los Angeles County, California. The dunes ranged from Ocean Beach (near Santa Monica) south to Magala Cove in Palos Verdes and were bordered on the west by the Pacific Ocean and the east by Los Angeles coastal prairie. The El Segundo blue occupied areas within the dunes with high sand content and its obligate host plant, coast buckwheat (Eriogonum parvifolium). The historic population size likely averaged 750,000 butterflies per year . The prairie has since been entirely converted to an urban landscape and the dunes reduced to about 307 mostly degraded acres. The extent of habitat loss peaked, and El Segundo blue numbers likely reached their nadir, in the late 1970s when virtually all of the dunes were developed or degraded. Restoration efforts were initiated in the 1980s and continue to this day. Virtually all remaining potential habitat was protected from private development due geological, conservation and other restrictions by 1990 and was believed to be capable of supporting 100,000 butterflies if fully restored . Governmental development, especially by the City of Los Angeles and the Los Angeles Airport (LAX) is still a significant threat .
Currently, there are three extant populations (Airport Dunes, Chevron butterfly preserve, and Malaga Cove) and two potential populations (Ballona Wetlands and Hyperion).
To end a long conflict with its neighbors, LAX condemned and removed 822 homes from 200 acres on its western border between 1966 and 1975, leaving a severely degraded but potentially restorable section of the El Segundo Dunes . The El Segundo blue was placed on the federal endangered species list in 1976, beginning a long, and to this day continuous, effort to restore the Airport Dunes for the butterfly and other native species. LAX has alternately sought to restore and destroy El Segundo blue habitat on the site. In 1975, about 70% of the back dune was excavated and recaptured to realign Pershing Drive . The area was reseeded with California buckwheat (Eriogonum fasciculatum) which attracted competing non-native moths and butterflies, suppressing El Segundo blue numbers. The foredune to the south and west, and last fragment of coastal prairie were graded during this same period. Only about 40 of the 200 acres escaped degradation during the 1970s. The impacts extirpated 17 of 20 native mammals, 7 of 31 butterfly species, 7 of 18 amphibians and reptiles, and all 5 coastal scrub obligate birds . Twenty-two of 73 native species present in 1940 were absent in 1989 and 19 of 51 of extant native plants were represented by less than 100 individuals . LAX proposed developing the dunes as recreational site with a 27 hole golf course and a 92 acre butterfly preserve in 1982 . In 1985 the California Coastal Commission refused to issue a permit for the project. In the late 1990s, LAX proposed to extend runway into the dunes .
In 1987 the City of Los Angeles initiated efforts to reduce California buckwheat and increase coast buckwheat populations. In 1992, the City of Los Angeles establishes a 203 acre Habitat Restoration Area within the dunes. Restoration efforts have continued to this day. These efforts significantly increased the size of the El Segundo blue population at the Airport Dunes, but the precise level of increase is not known because of inconsistent survey methodologies .
The population rose from approximately 400-700 in 1984 to 2,700-5,900 in 1989, then either declined or remained relatively stable through 1993 before dropping to 1,000-1,300 in 1994 . The population is known to have grown since then in response to restoration efforts, but counts are not comparable to earlier studies due to changed methodologies and survey efforts. Experts  believe the population size is certainly less than the 72,000 projected by recent LAX consultants .
CHEVRON BUTTERFLY PRESERE
The 1.6 acre Chevron butterfly preserve has been isolated by development since the 1950s . It is estimated to have supported about 2,000 butterflies from 1965 to 1976 . The population dropped to 1,600 in 1977, 681 in 1979, 400 in 1986 . The decline may have been caused by dune stabilization or lepidopterists criss-crossing the small site, using a capture-release method that can harm butterflies, and removing 839 butterfly larvae for study . In 1986, the preserve had 240 host plants and 1,000 introduced seedlings . The 1996 population was estimated at 5,000 to 7,000 butterflies on 1,200 host plants . The population increase has been attributed to intensive management for the El Segundo blue .
The El Segundo blue population was discovered on an eroded and iceplant dominated site in Malaga Cove in 1983 . It had sixty butterflies and less than 50 host plants on 1 acre in 1984 . It was fenced in 1986 . Host plants and butterfly populations in 1990 were similar to the 1984 count . The site was degraded by illegal dumping in 1997 . In 2004 it supported 10-30 butterflies . An adjacent population was discovered in 2000 in coastal bluff scrub habitat at York Long Point .
A single male was reported but not captured at a potentially suitable six acre private land site within Ballona Wetlands in 1985 . Fifteen host plants but no butterflies were found there on a small dune fragment in 1986 . By 1989 half the plants were dead . A seven acre site was seeded with native plants in 1990 but was significantly disturbed by a lagoon restoration project in 1997 . The U.S. Fish and Wildlife Service issued a permit to reintroduce the species prior to 1990, but the program has not been carried out .
A single butterfly was observed in the late 1980s near a remnant dune on a 30 acre site east of the Hyperion sewage treatment plan . The site was extensively planted with exotic vegetation in 1995 by the cities of El Segundo and Los Angeles .
 USFWS. 1998. El Segundo Blue (Euphilotes battoides allyni) Recovery Plan. U.S. Fish and Wildlife Service, Portland, OR.
 Mattoni, R. 1990. The endangered El Segundo blue butterfly. Journal of Research on the Leptidoptera 29(4):277-304.
 Mattoni, R., T. Longcore, C. Zonneveld and V. Novotny. 2001. Analysis of transect counts to monitor population size in endangered insects: the case of the El Segundo blue butterfly, Euphilotes battoides allyni. Journal of Insect Conservation 5:197-206.
 Rich, C. 2003. Letter from Catherine Rich, Executive Director, The Urban Wildlands Group, to Cindy Miscikowski, Los Angeles Councilwoman, August 4, 2003.
 Longcore, T. 2005. Personal communication with Travis Longcore, The Urban Wildlands Group, October 10, 2005.
 Sapphos Environmental, Inc. 2005. LAX Master Plan Final EIS, Appendix A-3c: Los Angeles/El Segundo Dunes Habitat Restoration Plan. Los Angeles World Airports, U.S. Department of Transportation, and Federal Aviation Administration.