Box Turtles (Terrapene carolina bauri) on Ancient, Anthropogenic Shell Work Islands in the Ten Thousand Islands Mangrove Estuary, Florida, USA
We investigated the ecology, distribution, and density of Florida Box Turtle (Terrapene carolina bauri Taylor, 1895) populations in the Ten Thousand Islands (TTI), an estuarine mangrove ecosystem in southwestern Florida. The distribution and ecology of Box Turtles in this region and this habitat type have not been previously investigated. The study area encompassed 18 islands and included five natural islands, 13 man-made shell islands, and adjacent mangrove environments. Two hundred and twenty-nine live Box Turtles and 95 Box Turtle shells were detected a total of 409 times on seven of the 18 islands. The seven islands where Box Turtles were detected ranged in size from 7.3 to 31.0 ha and were ancient shell work sites, apparently constructed by the Calusa or other Prehistoric Indians approximately 1,900 to 900 years before present (ybp). Box Turtles were not detected on natural islands. We detected Box Turtles primarily in subtropical hardwood hammock forests, but we detected 10% of turtles in mangrove or mangrove ecotones. Males were larger than females across all sites. We detected a significant difference in body size between living and dead adults. We estimated population size on four shell work islands to range from 43 (SE = 3.5) turtles to 270 (SE = 244) turtles and estimated densities ranging from 2.7–12.2 turtles/ha. Box Turtles on the shell work islands of the TTI are a unique example of populations living on ancient, manmade islands. However, known populations are small and isolated and may be susceptible to increased human recreational use, mechanized vegetation management, or predation by raccoons.Abstract
Map of the northern Ten Thousand Islands mangrove estuary in Collier County, Florida, United States. The three rectangles designated A, B, and C represent clusters of survey sites. Six survey locations are located within Area A; nine survey locations are located in Area B; and three survey locations are located in Area C.
Time between Terrapene carolina bauri encounters vs. month of survey at Site K in the Ten Thousand Islands region, Collier County, Florida, United States. We only plotted data from Site K because survey effort was not distributed evenly among islands and seasons, and our largest survey effort was focused on Site K. Sample sizes are reported in parentheses below each month.
Cumulative distribution of search intervals between Terrapene carolina bauri encounters on islands with documented turtle populations in the Ten Thousand Islands region, Collier County, Florida, United States. Ninety-five percent of the search intervals ended with a Box Turtle encounter in less than 4.5 person-hours.
The frequency with which simulations resulted in detecting Terrapene carolina bauri on the same number (7) of islands as in our surveys of 18 islands in the Ten Thousand Islands region, Collier County, Florida, United States. Each bar represents 10,000 simulations of the corresponding number of T. c. bauri populations distributed randomly amongst the 18 islands.
Terrapene carolina bauri search effort at 18 natural and human-made islands in the Ten Thousand Islands region, Collier County, Florida, United States. Symbol size is proportionate to island size (contiguous area of upland habitat). Shaded points represent islands where turtles were found. Horizontal line represents approximate effort needed to demonstrate absence of turtle populations with densities similar to the documented populations, with 95% confidence.
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