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The Bottom Line, Primary Cause's of the Extinction of Local Populations
The Hypothetical Graphical Model  (based on this current local population as of 8-24-16)
At this point in time, 2016, this local population consists of a number of core members residing in 4 basic sub-groups.  The members of each sub-group rarely interact with members of other sub-groups.
This season (2016) three females (M24, M1, and M9) crossed the road to nest and one male (M14) crossed the road, returning to his former Primary Activity Area after a 3 year absence.

Nine new turtles were found (M39 thru M47) this season, and two turtles (M16 a male, and M39, a female)  were found dead in the woods of disease or natural causes (not trama or injury).

Turtles M1(f) and M24(f) successfully re-crossed the road with help (carried across by hand) but turtle M9 was killed by a vehicle when she tried to re-cross the road, 1 or 2 days before expected.   Turtle M14 was injured during his road crossing, but survived the season.
The meadow sub-group (yellow), consisting of 2 females and 3 males, all being young adults, M25(f), middle aged adults; M18(m), M11(f) and M30(m)  or older adults; M29(m).  These turtles face dangers of mowing equipment, but they have never been observed to cross public roads, with one small exception.  M25(f) was killed in 2017 by mower tractor.
The south slope sub-group (aqua), consists of 2 females (M1 and M6) and 2 males (M12 and M32), all being middle aged or very old adults.  The two females make road crossing every year or two.  The males never travel close to any public roads.
The tank road sub-group (red), consists of 3 males M8(m), M10(m) and turtle M14(m), a small male, who re-joined this group after a few years away.   Turtle M9(f), a small, active female, possibly the most important member of this sub-group, was killed while crossing the road in July, 2016 returning from a nesting forray.
The Edsel Hollow sub-group (orange), consists of males M15, M19 and M27, and female M38.  Other turtles found in this area over several years have turned out to be likely transients including M20, M39, M40, M5 and M23.
The photo to the left shows the travels of the core members of this local population's 4 sub-groups for the past 9 years.
It might appear that members of the Meadow Group (yellow) interact often with members of the Tank Road (red) and South Slope (aqua) groups. But in reality, the visits (road crossings) by members of the other groups are by females on nesting forrays.  All red line road crossings were by one turtle:  M9 (f), now dead by vehicle.

The aqua road crossings are by turtles M6(f), M24(F) and M1(f).  Except for one observed mating between M30 and M6, no other interactions have been observed between these two groups' members.
Any Eastern Box Turtle local population who's residents' combined home ranges are bisected by any public road, is doomed to extinction, as adults, primarily, but not exclusively females, are removed, resulting in recruitment diminishing eventually to zero, and the remaining relic adults die as a result of old age and disease.
Development and habitat destruction are often cited as primary causes of Box turtle population demise, but research confirms that most urban turtle mortality is from vehicles.  Some turtles die from leaf and brush burning and some from lawn mowing, but most mortality is from vehicles during road and street crossings.

Road crossings also account for the taking some turtles for pets, and other turtles being moved and released away from their home ranges.  Turtles that are moved from their established home ranges, attempt to travel (home) back, but research suggests that if moved too far, Box turtles are unable to return, and possibly wander about the remainder of their lives.

Eastern Box turtles don't generally establish new home ranges when they loose their old ones.  Some research suggests that Box turtles maintain 2 (or more) home ranges, and some say that Box turtles will extend their home range when in search for food and other resources, but most research suggests that once a young Box turtle establishes a home range, they will stay there for life.

Diseases cause turtle deaths, and evolving diseases may someday become the primary cause of sudden death in Box turtles.
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As road-crossing females are removed by vehicles, one by one, contact among sub-groups diminishes, mating opportunities for the remaining females decreases, and the amount of new recruitment, already extremely low, is reduced even more.
Not all adult Box turtles are road-crossers, and not all Box turtle residents have activity areas that are bisected by roads,  but unless every adult male and every adult female turtle in a local population is replaced by a  juvenile, surviving at least until sexual maturity, and each of those individuals is also replaced by additional surviving recruitment, and so on in perpetuity, the entire population will vanish.
Population Recruitment and Mortality Modeling link is located here
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Eastern Box Turtle
                Terrapene carolina carolina
A Relict Population Doomed To Extinction?
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