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Eastern indigo snakes have been characterized as a “late-maturing colubrid snake”. These traits include high adult survivorship, high longevity, low to medium fecundity, small annual clutches, low juvenile survivorship, male-biased sexual size dimorphism, high ratio of mature to immature individuals in the population, and a significant proportion of the population that is older than 4 years old.
Sexual maturity in eastern indigos is reached in 3 to 5 years of age with a total length approaching 1.5-1.8 m. Male eastern indigos are estimated to reach sexual maturity in 2-3 years, and females in 3-4 years. In southeast Georgia, it is assumed that males typically do not attempt to breed until 2-3 years old, and females typically breed at 3-4 years old; however, exceptions can occur as a two year old captured in Georgia was found to be gravid. A skewed sex ratio of 2:1 male to female was found at a Georgia study site, and may be the result of higher energetic costs associated with reproduction, higher predation rates, and/or higher overwinter mortality in females.
Eastern indigo snakes are active in the winter; emerging from refugia during suitable temperatures to bask and breed. With the advent of cooling temperatures and shortening day lengths in autumn, adult eastern indigos concentrate on sand ridges and other upland habitats to breed. Competition among males for mates may be intense, resulting in male-male combat rituals. This involves the males intertwining as they wrestle and fight; sometimes biting each other on the neck and inflicting deep gashes. The height of the mating season is November through January, but breeding can occur from October through March.
Females lay a single clutch of 4-14 large eggs between April-June, usually in an open-canopied sandy microhabitat. Eggs measure approximately 7.6cm in total length. The eggs are soft shelled, oval, and granular-surfaced. Females have the ability to retain live sperm for prolonged periods, possibly over 4 years, for later release and egg fertilization. Reports of nest sites are rare, but appear to be mostly associated with gopher tortoise burrows; especially abandoned burrows. Eggs hatch in August-September, and neonates measure 40.6 – 61 cm upon hatching.
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