The common snapping turtle (Chelydra serpentina) is a widespread reptile known for its longevity, often living for many decades in the wild. This long lifespan supports a reproductive strategy involving laying a substantial number of eggs annually. Although a single female produces a large clutch, egg survival rates are notoriously low, meaning prolific reproduction yields few survivors.
Clutch Size and Nesting Vulnerability
The clutch is the total number of eggs laid in a single nesting event. Clutch size is highly variable, generally averaging between 20 and 40 eggs, though larger females may lay up to 80 eggs. The size and age of the female are the primary determinants, with larger, older turtles producing more eggs.
In late spring or early summer, the female leaves her aquatic habitat and travels to find a suitable nesting site, often choosing sandy or gravelly soil in a sunny, well-drained location. She uses her hind legs to excavate a flask-shaped hole, deposits the eggs, and covers them with soil before returning to the water. The mother provides no further parental care, leaving the nest immediately vulnerable. This vulnerability includes poor site selection, which can expose eggs to temperature extremes, or damage to the soft eggs during the laying process.
Predation: The Dominant Threat
Predation is the most significant factor determining the fate of snapping turtle eggs, accounting for the vast majority of all egg loss. Studies frequently report that 80% to over 90% of all nests are destroyed annually by predators, often within the first 24 to 48 hours after the female has left.
The main culprits are opportunistic, medium-sized mammals (mesopredators) that thrive near human-altered landscapes. These predators locate nests by following the scent trail left by the female.
Primary Predators
The primary predators include:
- Raccoons
- Skunks
- Foxes
- Coyotes
Badgers, crows, and ravens also contribute to nest destruction. Once located, a predator can quickly excavate and consume the entire clutch. The nesting season, from late May through early July, coincides with a period of high activity for these mammals, exacerbating the risk. In some locations, predation rates have reached 100%.
Environmental Conditions Affecting Incubation
Beyond predation, eggs must contend with a narrow set of environmental conditions for successful incubation. Temperature is one of the most important abiotic factors because the common snapping turtle exhibits temperature-dependent sex determination (TSD). The nest temperature determines the sex of the embryo: a narrow middle range produces males, while cooler or warmer extremes result in females.
Temperatures that are too cold or too hot can be lethal, resulting in non-viable clutches. The second critical factor is moisture, which must be maintained within a specific range.
Too much moisture, such as from flooding, can drown the eggs or facilitate fungal and bacterial infections. Conversely, soil that is too dry leads to desiccation, causing the embryo to die. Deviations from the optimal range significantly reduce the odds of successful hatching.
Overall Survival Rates and Population Dynamics
Synthesizing the numerous threats, the overall survival rate for snapping turtle eggs is remarkably low. On average, only about 5% of all eggs laid successfully hatch. This metric only represents the end of the incubation period, not the survival of the species.
Hatchlings that emerge still face significant predation and environmental risks as they attempt to reach the water. Consequently, survival to adulthood, which can take 15 to 20 years in northern populations, is drastically lower.
A commonly cited statistic indicates that only about 1 in 1,000 to 1 in 1,400 eggs laid will survive long enough to reach reproductive maturity. This high mortality rate is characteristic of long-lived species that offset early losses by having many offspring over a long reproductive lifespan. Since adult snapping turtles have few natural predators and live for decades, protecting mature breeding individuals is important for population stability.