Eastern Indigo Snake

Drymarchon corais couperi

Description

The Drymarchon coralis couperi (eastern indigo snake) is one of the largest and stoutest colubrid snakes of North America, attaining a maximum length of about 8.5 ft (2.5 m). The head is barely distinct from the neck. Scales, arranged in 17 rows at midbody, are large, smooth, and shiny. The body color is a uniform lustrous blue-black. The chin, throat, and cheeks are tinged with red or cream. Smaller eastern indigo snakes may superficially resemble the common black racer (Coluber constrictor ).

Behavior

The indigo snake feeds largely on fish, frogs, toads, snakes (poisonous as well as nonpoisonous), lizards, turtles, turtle eggs, small alligators, birds and small mammals. The eastern indigo snake is highly dependent on burrows excavated by other animals, particularly the gopher tortoise (Gopherus polyphemus ). These burrows are used as a refuge and for overwintering. The gopher tortoise, itself, is included on the federal list as a Threatened species.

The eastern indigo snake may show seasonal shifts in habitat occupancy, wintering on sand ridges but moving to adjacent, more mesic habitats during the summer. It does not, however, exhibit true migration.

Breeding occurs from October to March and is promiscuous A single clutch of four to 12 eggs is laid during May. Eggs hatch in approximately three months. Sexual maturity may be reached in three to four years. Delayed fertilization is apparently possible; there is a single record of a captive snake laying five eggs (at least one of which was fertile) after being isolated for more than four years.

Habitat

The indigo snake inhabits mature pine forests in central and northern Florida, and flatwoods, dry glades, tropical hammocks, and muckland fields in southern Florida. It is often found along canal banks, using crab holes for dens. In Georgia it inhabits "sandhill" regions, dominated by mature longleaf pines, turkey oaks, and wiregrass. This plant community is adapted to periodic fires. When fires are suppressed, laurel oaks and associated hard-woods succeed, making the habitat unsuitable for the eastern indigo snake. The gopher tortoise plays an integral role in maintaining wildlife in the sand-hill ecosystem.

Outside peninsular Florida, D. c. couperi is largely restricted to the vicinity of xeric habitats supporting populations of gopher tortoises, Gopherus polyphemus, although D. c. couperi moves seasonally into more mesic habitats. The snake utilizes gopher tortoise burrows for shelter and possibly breeding. Throughout peninsular Florida, D. c. couperi may be found in all terrestrial habitats which have not suffered high density urban development. They are especially common in the hydric hammocks of the Gulf hammock region of north Florida and in similar habitats throughout peninsular Florida. The species is also found around the periphery of and along drainage canals that bisect citrus groves throughout Florida.

Due to their large home range and diurnal habits the species is particularly vulnerable to being killed by people or domestic animals. They remain in the greatest numbers in areas where extensive tracts of wild land are still to be found.

Distribution

The species, D. corais, ranges from the coastal plain of the southeastern United States to northern Argentina. Of this broad group of snakes, only the eastern indigo and the Texas indigo subspecies are found within the United States. Historically, the eastern indigo snake ranged from South Carolina through Georgia and Florida to the Keys, and west to southern Alabama. Some evidence suggests that the snake also occurred in Mississippi.

At present, the eastern indigo snake is found primarily in Georgia and Florida. It has been sighted recently in 50 Georgia counties and is particularly common in the southeastern quadrant of the state. It is considered locally abundant in Florida south of Sarasota. Populations are more fragmented north of Sarasota, and only a few small populations are known from the Panhandle. The species is now extremely rare, if it occurs at all, in Alabama, Mississippi, and South Carolina.

Threats

The decline of the eastern indigo snake mirrors the loss of mature longleaf pine forests in the South. In recent decades, agricultural and residential development have deforested millions of acres. Surviving stands of forest have been degraded by suppression of fire or by logging. Vast tracts of forest have been logged and replanted with fast-growing pines that can be more quickly harvested. These "young" forests cannot support the eastern indigo snake.

Urbanization and agricultural development have destroyed a large percentage of this species habitat. Where large tracts of otherwise suitable habitat remain, their suitability for D. c. couperi has often been diminished by declines in gopher tortoise population and their burrows that provide shelter for this snake. Thus, factors that reduce the suitability of tortoise habitat, such as fire suppression, reduce the suitability for the indigo snake as well. Gassing of tortoise burrows to flesh out rattlesnakes has been shown to be lethal to snakes as well. A steady loss of habitat has made this species more vulnerable to other human threats. Because it is large, conspicuous, and relatively slow, it often falls prey to people who "kill snakes on sight." On the other hand, commercial collectors value it for the pet trade because it is nonpoisonous, docile, and attractive. Mail order specimens can bring as much as US$225. Therefore, the eastern indigo snake is in the unenviable position of being killed by some and collected by others.

Because of its large home range, the indigo snakes is especially vulnerable to highway death in areas where its habitat has been fragmented by development, including surface mining activities.

Conservation and Recovery

The Recovery Plan calls for the following conservation measures. First, maintain and protect existing populations of the eastern indigo snake by locating and delineating present populations through field surveys and distribution studies as well as determining and providing needed habitat which includes acquiring and/or managing and protect areas necessary to maintain viable populations by controlling native vegetation through prescribed burning and/or selective thinning and conservative timber harvest techniques. In addition, studies of population ecology, movements, and food habits need to be made. In an effort to obtain better protection for this species, legislation protecting the eastern indigo snake in each state where it occurs or possibly occurs needs to be established including laws prohibiting the practice of introducing toxic substances into gopher tortoise burrows on public lands and to promote ending the practice on private lands inhabited by the eastern indigo snake. Also, legislation and/or regulations that will provide more protection for the gopher tortoise are needed. The second essential action that needs to be taken is to reestablish populations where feasible. This involves releasing the eastern indigo snake at chosen sites which have been identified as suitable reintroduction sites. In addition, it will be necessary to maintain a captive breeding program and to research captive breeding and restocking potential as needed. And a final action that needs to be taken is to improve the attitude of the public and their behavior towards the eastern indigo snake. This would involve educating the general public regarding the plight of the indigo snake and the need for recovery efforts by publishing scientific data and distributing educational materials for the media. A special effort to contact owners or leaseholders of large tracts of sandhill habitat where the eastern indigo snake possibly or does occur needs to be made, in order to inform landholders of the risks posed to this species.

The ultimate Recovery Plan objective is to delist the species by insuring that numerous the eastern indigo snake populations exist and are reproducing and protected where suitable habitat still exists in the historical range of the species. Before this can be accomplished research is necessary to: develop population monitoring methods; determine habitat requirements of juveniles; and determine captive breeding and restocking potential of the species. Establishment of protected areas of good habitat as reintroduction sites and sanctuaries is thought to be important as is the improvement of public attitude a behavior towards the eastern indigo snake.

Recovery tasks currently being carried out include habitat management through controlled burning, testing experimental miniature radio transmitters for tracking of juvenile Eastern indigo snake, maintenance of a captive breeding colony at Auburn University, recapture of formerly released snakes to confirm survival in the wild, presentation of education lectures and field trips, and efforts to obtain landowner cooperation in Eastern indigo snake conservation efforts.

Ultimately, the survival of eastern indigo snake, the gopher tortoise, the red-cockaded woodpecker (Picoides borealis ), and other endangered wildlife depends on the preservation of remaining tracts of mature, old-growth forests. This can be accomplished either through outright acquisition of land or by purchase of conservation easements. These efforts are hampered by the availability of funds.

Ideal indigo snake habitat is similar to that of the bobwhite and white-tailed deer, and management of national forests for these game animals will benefit the eastern indigo snake, as well. Beneficial management techniques include mechanical thinning and controlled burning to prevent overgrowth by hardwoods. Leases for logging on public lands that prohibit clear-cutting would preserve the snake's habitat. This snake apparently reproduces well in captivity, and reintroduction into the wild can be attempted once its habitat has been protected. In June 1989 the Interior Department created a new wildlife refuge for the Florida panther and other endangered species in south Florida. The 30,000-acre (12,140-hectare) Florida Panther National Wildlife Refuge is adjacent to the Big Cypress National Preserve and provides protected habitat for the Endangered wood stork (Mycteria americana ), Everglade snail kite (Rostrhamus sociabilis plumbeus ), bald eagle (Haliaeetus leucocephalus ), red-cockaded woodpecker (Picoides borealis ), peregrine falcon (Falco peregrinus anatum ), and eastern indigo snake.

Contact

U. S. Fish and Wildlife Service
Regional Office, Division of Endangered Species
1875 Century Blvd., Suite 200
Atlanta, Georgia 30345
http://southeast.fws.gov/

References

Behler, J., and W. King. 1979. The Audubon Society Field Guide to North American Reptiles. Alfred Knopf, New York.

Speake, D. W., et al. 1978. "Ecology and Management of the Eastern Indigo Snake in Georgia: A Progress Report." In R. Odon and L. Landers, eds., Proceedings of the Rare and Endangered Wildlife Symposium. Georgia Department of Natural Resources, Atlanta.

U.S. Fish and Wildlife Service. 1982. "Eastern Indigo Snake Recovery Plan." U.S. Fish and Wildlife Service, Atlanta.

Wharton, C. H. 1978. The Natural Environments of Georgia. Georgia Department of Natural Resources, Atlanta.