During nesting season (May-July), the Jekyll Island Causeway is patrolled by GSTC staff and researchers from the University of Georgia for crossing diamondback terrapins. The data collected from this monitoring program provides valuable information that helps guide the management of Jekyll terrapins.
Any turtle found alive and uninjured is safely removed from the road. Researchers take measurements that provide data about the local nesting population, as well as provide information on growth over time for recaptured animals. Animals found for the first time are marked with notches in the margins of their shells. These notches are placed on different scutes (scales) as part of a code system in which each terrapin has a unique notch pattern. Terrapins found in previous seasons are identified by decoding this pattern. Researchers also make note of where the turtle was found on the road, which direction it was heading in, and whether or not it was carrying eggs. After all the data has been collected, captured terrapins are released alongside the causeway. Care is taken to ensure that animals are released in locations where they will be least likely to head back across the road.
When injured turtles are found on the road, they are transported to the GSTC for assessment and care. Researchers still collect information on where the terrapin was found, as well as the direction it was traveling in. At the GSTC, a variety of techniques are used to help rehabilitate these injured terrapins.
Researchers also collect terrapins that have been hit and killed on the road. Just like with live and injured turtles, the location and direction-of-travel are noted for deceased individuals if they can be accurately determined. Deceased terrapins are also checked for notches, as well as examined for the presence of eggs. All viable eggs are extracted for artificial incubation as part of the GSTC’s rear and release program (see below).
As terrapins cross the road on their way to and from nesting, many are hit while still carrying eggs. These eggs can be collected from deceased individuals through extraction, or from injured individuals by using oxytocin and other drugs to induce them to lay. Intact eggs are cleaned, weighed and measured, and then placed into one of the GSTC’s incubators. Not all eggs will be viable, and clutches are checked regularly for signs of mold or rot. Constant temperature and humidity help provide an ideal environment for development, and after about 45 days in the incubator many eggs will begin to hatch. Hatchlings remain in the incubator until they have completed the hatching process, meaning they have fully absorbed the yolk sac from their eggs. Healthy hatchlings are weighed and measured, and then are released into the marsh at different sites around the Jekyll Island Causeway.
rear and release program
Each year, several hatchlings remain at the GSTC for participation in our Rear and Release Program. These turtles live in educational exhibits located at the end of the public walkway in the rehabilitation pavilion. Proper feeding and care allow these turtles to safely develop and grow as they give visitors a chance to view them and learn about their species. After spending a year as animal ambassadors, these turtles are released into the marsh off the Jekyll Island Causeway. It is hoped that their advanced size and health will provide them with an improved chance of survival to adulthood.
Incubation and Temperature-Dependent Sex Determination
Like most reptiles, the temperature inside a terrapin nest will determine whether its eggs develop as males or as females. Warmer temperatures typically produce female turtles, and cooler temperatures typically produce male turtles. As road mortality removes mainly females from the population, the incubators at the GSTC are purposefully set to warmer temperatures in order to produce mainly female hatchlings. It is hoped that released hatchlings survive to maturity and help replace some of the nesting females hit each summer on the causeway.
Beginning in 2007, terrapin crossing signs were installed on the Jekyll Island Causeway to alert drivers about the potential presence of nesting terrapins on the road. These signs are only posted during nesting season (May-July), so as to encourage drivers who may utilize the causeway year-round to be extra vigilant when terrapins are active.
Beginning in the summer of 2013, traffic signs equipped with flashing lights were installed to provide further warning to drivers. These lighted signs are located in areas where causeway monitoring has revealed high numbers of crossing terrapins. The lights are timed to flash only during peak crossing times, which are a half hour before high tide and up to two hours afterward. Continuing research will hopefully demonstrate if these new signs effectively warn drivers.
nest mounds and boxes
Terrapins cross the causeway as they seek high, dry ground in which to nest. Nest mounds were created alongside the causeway in order to provide high, dry habitat that entices terrapin females to stop and nest before crossing the road. These mounds are covered by caged boxes that are designed to allow terrapins in but keep potential predators, such as raccoons, out. There are 12 nest mounds located at six locations on the causeway. In the summer of 2013, wildlife cameras were used to monitor how often terrapin females chose to lay their eggs in several of the nest boxes.
Check out this poster by former Diamondback Terrapin AmeriCorps Member, Dan Quinn, to learn more about incubator and nest mound research at the GSTC!