Andrea ColtonViews:
For the past several months, I have been heading to a site in south-central Georgia to learn more about Eastern Box Turtle movements and home range sizes. One of the immediate lessons I learned straight away is how hard box turtles can be to find, especially when you really want to find them. Eastern Box Turtles spend their time on forest floors and, though they prefer more open forests, there is often a fair amount of leaf litter and understory vegetation present to conceal them. Due to visual obstructions, researchers are more commonly utilizing dogs trained to seek box turtles, as their noses can be more effective at finding turtles than the human eye. Unfortunately, we didn’t have a turtle dog in the budget, so it came down to a team of about ten people contributing 305 search hours to find turtles. For all that effort, we were able to find two adult females. The first was found on the first survey of the year, but it took nearly three months to find the second!
For both individuals, we attached transmitters so we could occasionally track them and a small GPS tag programmed to record their location every two hours. Both transmitters and GPS tags weigh very little, and we make sure that any weight added to a turtle’s shell is only 5% of its body weight to avoid weighing them down. I spent a large portion of my time during my master’s research tracking Ornate Box Turtles in Illinois and have always enjoyed doing radio telemetry work, but utilizing GPS tags on individuals is much more effective for fine-scale data. Tracking multiple animals every single day is a massive amount of work, and even then, you are only able to determine where they are at one specific moment of the day.
Even so, it is good practice to manually track to A) compare tracked locations to GPS tag locations to ensure accurate data is being collected, B) make sure you don’t lose the turtles by risking them wandering too far out of range of the radio receiver, and C) visually inspect the turtle for any signs of disease or distress and ensure all equipment is still working. So, how do we track manually? We need three pieces of equipment: a transmitter that emits a unique frequency, a radio receiver to pick up the frequency, and an antenna to amplify the signal. From there, we follow a beeping sound emitted from the radio receiver. We just head in the direction the beeping is loudest to find the turtle!
Each time I went out to track our two turtles, I ended up finding them a few hundred meters away from the last location I saw them. Both were largely found in longleaf pine uplands, but around mid-summer they made large movements towards wet, low-lying areas of forest and stayed there for a few weeks before moving back into upland. Perhaps the wetter, cooler forest provided relief from summer heat. Perhaps there is some seasonality to their foraging locations. While we don’t know the exact reason for the move, we do know that these areas provided something each turtle needed. The areas animals regularly utilize throughout their lives, whether it be for foraging, nesting, or thermoregulatory needs, are their home ranges.
Researchers can easily calculate home ranges by using “minimum convex polygons”. This simple analysis works by defining the area that encompasses 95% of the individual’s location data. For our turtles, we found that one uses 13 hectares while the other uses 36! This variation is consistent with other studies that have investigated turtle home range sizes. Largely, it seems the most consistent thing about turtles is that they are inconsistent! Likely, landscape variation and management practices between sites play a role in different behaviors exhibited by various populations, which highlights the importance of research at local levels.
