Use of GPS loggers to enhance radio-tracking studies of semi-aquatic freshwater turtles

Ecologists have spent many hours manually tracking the movements of animals in their habitat to determine their home range, and to ascertain their use of critical habitat and wildlife corridors. This is costly, logistically burdensome, and can disturb the animal from its natural patterns of behavior. The introduction of Global Positioning System (GPS) logging devices has greatly reduced the labor involved for tracking large mammals and migratory birds since the devices automatically acquire locational fixes at regular intervals throughout the day. For freshwater turtles, however, GPS logging devices may not be suitable because of their inability to obtain locational fixes when submerged in water, but when on land, they have the advantage of collecting a sufficiently large number of locational fixes to resolve short-term sojourns and fine-scale movements that are not possible with conventional telemetry approaches. In this paper, we used a combination of conventional radio-tracking plus GPS loggers to study the movements of several Blanding’s Turtles (three females in 2011; two males and two females in 2012). We predicted that the GPS loggers in combination with conventional telemetry would provide additional information that would transform our understanding of how the turtles used their habitat. With this enhanced tracking, we were able to: (1) arrive at a more complete mapping of habitat used by the Blanding’s Turtles; (2) identify novel areas of critical habitat that were not discovered during the process of radio-tracking; (3) determine movement corridors between critical habitat locations; and (4) uncover fine scale patterns of movement within wetland habitat. We discuss the advantages and disadvantages of GPS logging technology, and provide an approach to maximize effectiveness for tracking freshwater turtles.