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The
extent and vibrancy of this patch varies with geographic location.
Scales are
large and smooth, with the central 3 - 5 scale rows keeled in adult
males. There are 17 scale rows measured at mid-body, and the
anal plate is undivided. Juveniles measure 43 - 61 cm (17
- 24 inches) at hatching, are typically black, have narrow whitish
to bluish bands along the body, and are more red or cream colored
around the head (USFWS 1999; Conanat and Collins 1991).
Potentially
Misidentified Species:
Juveniles may be easily confused with southern black racers (Coluber
constrictor priapus) due to the pale patches around the chin
and cheeks. Black pine snakes (Pituophis melanoleucas
lodingi) are similar in color and size, but lack the iridescent
sheen of the indigo snake. They also retain a faint crossbanding
pattern on the tail that indigo snakes lack.
II. HABITAT AND DISTRIBUTION
Regional Occurrence:
The historic range of Drymarchon couperi included the coastal
plains of Georgia, Alabama, Mississippi, and possibly Southern South
Carolina. Currently indigo snakes primarily range throughout
Florida, including the Florida Keys, and into southern Georgia (Lazell
1989; Lawler 1977).
IRL Distribution:
Drymarchon couperi occurs throughout the IRL.
III. LIFE HISTORY AND
POPULATION BIOLOGY
Age, Size, Lifespan:
Eastern
Indigo snakes are the longest native snakes in the U.S. and grow
to lengths of 1.88 - 2.65 m (Ashton and Ashton 1981; King
and Krysko 2000).
Juveniles measure 43 - 61 cm (17 -24 inches)
at hatching.
Little information
is available regarding the lifespan of wild eastern indigo snakes;
however, captive snakes have been documented to live more than 25
years (Shaw 1959).
Abundance:
Though they occur throughout Florida, eastern indigo snake populations
are declining to the point where they are considered rare in many
areas.
Reproduction:
Drymarchon
couperi reaches sexual maturity at approximately 3 - 4 years
of age (Hallam et al. 1998). In North Florida, breeding occurs
November - April. Wild females lay clutches of 4 - 12 eggs
in May or June (Moler 1992), while captive females have an average
clutch size of 9 -20 (Speake et al. 1987). Hatching takes
place after approximately 3 months, with peaks occurring August
- September. In south-central Florida, breeding occurs June
- January, with egg laying taking place April - July. Hatching
generally occurs from mid-summer through early Fall (USFWS 1999).
Females can apparently store sperm
and delay fertilization of eggs. Carson (1945) reported a
on a female indigo snake that laid a clutch of 5 eggs after having
been isolated for more than 4 years. There have also been
anecdotal reports of parthenogenetic reproduction in virginal snakes
(USFWS 1999).
IV. PHYSICAL TOLERANCES
Temperature:
Drymarchon couperi is cold-sensitive and requires shelter
when winter temperatures below approximately 10 °C (50 °F).
Most often refuge is taken in gopher tortoise burrows (Bogert
and Cowles 1947; Speake et al. 1978).
In wetter habitats where
gopher tortoises do not occur, indigo snakes take refuge in hollow
logs and the burrows of rodents, land crabs, and armadillos (Lawler
1977; Moler 1985a; Layne and Steiner 1996).
Other Physical Tolerances:
Desiccation:
Under
laboratory conditions, Drymarchon couperi showed a high
susceptibility to desiccation, and thus seeks out cool, underground
burrows or similar cover as shelter against extreme heat and dryness
(Bogert and Cowles 1947; Speake et al. 1978; Moler 1985a).
V. COMMUNITY ECOLOGY
Trophic Mode:
As
they lack venom and do not constrict, eastern indigo snakes attack
any vertebrate small enough to be overpowered and killed with their
strong jaws. They have been observed to flush prey from cover,
then give chase (Layne and Steiner 1996). They also occasionally
climb trees or shrubs in search of prey. The diet includes
toads, frogs, lizards, other snakes (including venomous types),
turtles, turtle eggs, gopher tortoises, small alligators, birds,
and rodents. Juveniles consume primarily invertebrates (USFWS
1999; Layne and Steiner 1996; Steiner et al. 1983).
Activity Time:
Diurnal.
Habitats:
Drymarchon couperi utilizes
a variety of habitat types and shows some preference for open, undeveloped
uplands. Typical habitats include pine flatwoods, scrubby
flatwoods, high pine, dry prairie, tropical hardwood hammocks, marshes,
coastal dunes and scrub, and mangrove forests (Steiner et al. 1983;
USFWS 1999).
In Georgia and Northern
Florida, indigo snakes can be temperature-restricted to sandhill
areas where gopher tortoises burrows are available to shelter in
when winter temperatures drop below approximately 10 °C.
In peninsular Florida, where winter temperatures are not typically
challenging, indigo snakes are found in all terrestrial habitats
that are not densely developed. Along the coast, indigo snakes
frequently use sandy ridges and hammock areas (Moler 1985b).
Drymarchon couperi
move between habitats frequently, especially during the summer and
fall (Moler 1985a), and thus have extensive home ranges. Speake
et al. (1978) reported home range sizes for indigo snakes in Georgia
averaging 4.8 ha in winter (December - April) and 42.9 ha in late
spring and summer (May - July). Moler (1985a) reported that
adult males utilize larger areas then either females or juveniles,
perhaps encompassing 224 ha. Layne and Steiner (1996) reported
male home range size as averaging approximately 74 ha (with a maximum
of 199.2 ha), while females averaged approximately 19 ha (with a
maximum of 48.6 ha).
Associated Species:
Drymarchon couperi can often be found in association with
gopher tortoises (Gopherus polyphemus) and other organisms
that share tortoise burrows, including the eastern diamondback rattlesnake
(Croatalus adamanteus).
VI. SPECIAL STATUS
Special Status:
Drymarchon couperi has been listed
as Threatened in the State of Florida since 1971. It has been
Federally listed as Threatened since Jan 31, 1978. The decline
of eastern indigo snakes is primarily the result of over-harvesting
for the pet trade, but habitat loss and degradation, and the gassing
of tortoise burrows to collect rattlesnakes have also heavily impacted
the species (Speake and Mount 1973; Speake and McGlincy 1981).
Law
enforcement of prohibitions against unauthorized take has reduced
pressure on the indigo snake, but has not eliminated it (Moler 1992).
Because this snake has a large home range, it may be especially
susceptible to habitat loss and fragmentation (Lawler 1977; Moler
1985a). Some estimates suggest that habitat losses of approximately
5% per year continue to occur (Lawler 1977). Increased human
population growth also increases the possibility of increased snake
mortality due to deaths from property owners and domestic pets.
It is expected that the increasing trend toward altering natural
areas for agricultural, residential and commercial purposes will
result in a large number of isolated groups which cannot support
a sufficient number of individuals to ensure continued survival.
Recovery
of Drymarchon couperi requires protection and preservation
of large expanses of unaltered habitat (USFWS 1999). However,
relatively little is currently known about the minimum population
size required to maintain and recover the species, though research
and population modeling efforts are underway to address these issues.
Management
activities being currently undertaken include prescribed burning
to maintain optimum habitat quality, maintenance of a captive breeding
colony, public outreach and education, and landowner cooperation
to conserve snake populations on privately held lands.
VII.
REFERENCES
Ashton R. and P. Ashton. 1981.
Handbook of Reptiles and Amphibians
of Florida. Windward Publishing,
Inc. Miami, FL.
Bogert, C. and R. Cowles. 1947.
Results of the Archbold expeditions.
No. 58. Moisture loss in relation
to habitat selection in some Floridian
reptiles. American Museum Noviciates
1358:1 - 55.
Carson, H. 1945. Delayed fertilization
in a captive indigo snake with a note
of feeding and shedding. Copeia 1945(4):222-224.
Conant R. and J.T. Collins. 1991.
A Field Guide to Reptiles and Amphibians.
Houghton Mifflin Company, Boston, MA.
Hallam, C.O., K. Wheaton, and R. Fischer.
1998. Species profile: Eastern
indigo snake (Drymarchon corais couperi)
on military installations in the
Southeastern United States. Technical
report SERDP-98-2, March 1998.
Strategic Environmental Research and Development
Program, U.S. Army
Corps. of Engineers, Waterways Experiment
Station, Vicksburg, MS.
King, F.W. and K.L. Krysko. 2000.
Online Guide to the Snakes of Florida.
Florida Museum of Natural History, University
of Florida, Gainesville,
FL. 266 pp. Available at http://www.flmnh.ufl.edu/natsci/herpetology/
fl-guide/onlineguide.htm.
Lawler, H.E. 1977. The status of Drymarchon
corais couperi (Holbrook),
the eastern indigo snake, in the southeastern
USA. Herpetological Review
8(3):76-79.
Lazell, J. 1989. Wildlife of the Florida
Keys: a Natural History. Island Press.
Washington, DC.
Moler, P.E. 1985a. Home range and seasonal
activity in the eastern indigo
snake, Drymarchon corais couperi,
in northern Florida. Final performance
report, Study E-1-06, III-A-5. Florida
Game and Fresh Water Fish
Commission; Tallahassee, FL.
Moler, P.E. 1985b. Distribution of the
eastern indigo snake, Drymarchon
corais couperi, in Florida.
Herpetological Review 16(2):37-38.
Moler, P.E. 1992. Eastern indigo snake.
Pps 181 - 196 in: P.E. Moler (ed).
Rare and Endangered Biota of Florida, Volume
III, Amphibians and
Reptiles. University Press of Florida,
Gainesville, FL.
Shaw, C.E. 1959. Longevity of snakes
in the U.S. as of January 1, 1959.
Copeia 1959(4):336-337.
Speake, D.W. 1993. Indigo snake recovery plan
revision. Final report to the U.S.
Fish and Wildlife Service; Jacksonville,
Florida.
Speake, D.W., and R.H. Mount. 1973. Some possible
ecological effects of
"rattlesnake roundups" in the
southeastern coastal plain. Proceedings
of the annual conference of the Southeastern
Association of Fish and
Wildlife Agencies 27:267-277.
Speake, D.W., J.A. McGlincy, and T.R. Colvin.
1978. Ecology and management
of the eastern indigo snake in Georgia:
A progress report. Pages 64-73
in: R.R. Odum and L. Landers, (eds.), Proceedings
of rare and endangered
wildlife symposium, Georgia Department
of Natural Resources, Game
and Fish Division, Technical Bulletin WL
4.
Speake, D.W., and J.A. McGlincy, 1981. Response
of indigo snakes to gassing
of their dens. Proceedings of the annual
conference of the Southeastern
Association of Fish and Wildlife Agencies.
35:135-138.
Speake, D.W., D. McGlincy, and C. Smith. 1987.
Captive breeding and
experimental reintroduction of the eastern
indigo snake. Pps. 84 - 90 in:
R.R. Odom, K.A. Riddleberger, and J.C.
Ozier (eds.), Proceedings.
3rd Southeastern Nongame and Endangered
Wildlife Symposium, Georgia
Department of Natural Resources, Game and
Fish Division.
Steiner, T.M., O.L. Bass, Jr., and J.A. Kushlan.
1983. Status of the eastern
indigo snake in southern Florida National
Parks and vicinity. South Florida
Research Center Report SFRC-83/01, Everglades
National Park;
Homestead, Florida.
U.S. Fish and Wildlife Service USFWS). 1982.
Eastern indigo snake recovery
plan. U.S. Fish and Wildlife Service, Atlanta,
Georgia.
U.S. Fish and Wildlife Service (USFWS).
1999. South Florida multi-species
recovery plan. Atlanta, GA.
2,172 pp.
Report by:
K. Hill, Smithsonian Marine Station
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