The North American box turtle (Terrapene) is a terrestrial reptile known for its highly domed shell and exceptional longevity. These long-lived creatures, which can survive for many decades, have a reproductive strategy characterized by low annual output. They produce a relatively small number of offspring per reproductive event, relying instead on the female’s ability to reproduce over a long period to sustain the population.
How Many Eggs Are Laid Per Season
The number of babies a box turtle produces is modest, with females laying a small quantity of eggs in each clutch. The average clutch size generally falls within the range of two to eight eggs, though some individuals may lay as few as one or as many as eleven eggs. The size of the female often dictates the number of eggs she can produce, with larger turtles typically laying bigger clutches.
Female box turtles are capable of producing more than one clutch during the mating season, which typically runs from spring into summer (May through July). While some individuals may produce only one clutch, others can lay up to three separate clutches in a single year. For example, the Common Box Turtle (Terrapene carolina) often averages a clutch size of four to five eggs.
The total number of eggs laid annually is the product of the small clutch size multiplied by the number of clutches. This results in a low reproductive rate compared to many other reptile species. Species within the Terrapene genus, such as the Eastern Box Turtle (T. carolina) and the Ornate Box Turtle (T. ornata), have slightly varied averages in clutch size, but the general pattern of low fecundity remains consistent.
The Reproductive Cycle and Nesting
The reproductive season for box turtles begins in the spring and continues through the summer and fall. A key aspect of their reproduction is the female’s ability to store sperm within her oviducts after mating. This mechanism, known as delayed fertilization, allows a female to lay viable, fertilized eggs for several years—sometimes up to four years—following a single successful mating encounter.
When it is time to lay eggs (typically mid-May to late June), the female searches for a suitable nesting site. She seeks a location with well-drained, loose soil that is exposed to the sun to provide warmth for the developing eggs. Using her hind legs, the female meticulously digs a flask-shaped nest cavity that can be several inches deep.
After depositing the elliptical, leathery-shelled eggs, the female carefully covers them with soil, concealing the nest before leaving. Incubation time is highly dependent on environmental factors, particularly soil temperature, but generally lasts between 50 to 100 days. Soil temperature also determines the hatchlings’ sex, a phenomenon called temperature-dependent sex determination.
Survival Rates of Young Box Turtles
The small number of eggs laid per season is offset by an extremely high mortality rate among eggs and hatchlings. Since there is no parental care, developing embryos and emerging hatchlings are vulnerable to a host of threats. Predation is a major factor, with animals like raccoons, skunks, foxes, and snakes frequently raiding nests for eggs.
Hatchlings are highly susceptible to predation because of their small size and soft shells upon emergence. They do not develop the hinged plastron that allows adult box turtles to completely seal themselves inside their shells until they are about four to five years old. This means they lack the primary defense mechanism of the adult turtle during their first few vulnerable years.
Very few box turtles survive their first year of life. Studies indicate that, on average, only a fraction of hatchlings survive long enough to reach adulthood, with survival rates sometimes as low as one in a thousand. Furthermore, survivors do not reach sexual maturity until they are seven to ten years old or more. This combination of low annual output and high juvenile mortality necessitates the box turtle’s long lifespan to ensure the species’ continued existence.