Populations in Michigan and elsewhere have been marked and recaptured for decades, giving individual histories rather than estimates. Those records include females confidently over seventy years old that continue to nest, and analyses have found clutch size and egg viability holding steady or even rising with age rather than falling.
That pattern, sometimes called negligible senescence, is described in several long-lived turtles, and it changes what conservation has to protect. In a species where a female may contribute clutches over half a century, removing one adult costs far more future recruitment than losing a nest.
The threat matches the vulnerability exactly. Blanding's turtles travel long distances overland between wetlands, especially nesting females in early summer, and road mortality falls disproportionately on those adults. The species is listed as Endangered in Canada and is protected across much of its United States range.