Assuming that 4.7 eggs are laid per season, that all eggs are fertile
and all hatch, that all young survive to maturity, that half the
hatchlings are females, and that females first lay eggs in the
eleventh year, the progeny of a single mature female would number 699
after twenty years. Considering that infertility and prenatal
mortality eliminate approximately 40 per cent of eggs laid (according
to laboratory findings) the average number of surviving young per
clutch would be 2.8 and the total progeny, after 20 years, would be
270, provided that only one clutch of eggs was laid per year. But it
is thought that, on the average, one third of the female population
produces two clutches of eggs in a single season. If the second clutch
contains 3.5 eggs (resulting in 2.1 surviving young when factors of
infertility and prenatal mortality are considered), the progeny of a
single female, after 20 years, would number approximately 380.
Postnatal mortality reduces the progeny to a still smaller number.
The small number of eggs laid each year and the long period required
to reach sexual maturity make the reproductive potential of _T.
ornata_ smaller than that of the other turtles of the Great Plains,
and much smaller than nearly any of the non-chelonian reptiles of the
same region.