Accuracy and location success of an ultralite GPS unit

Abstract

Technological advances in GPS tracking units for wildlife have led to smaller and lighter devices. Increased battery life allows for collection of more locations. Before a new device is used in the field, it is important to evaluate its performance in order to more accurately interpret the raw data collected. Our objective was to determine the accuracy and location success of the G10 Ultralite GPS logger for potential use in a study of wood turtles (Glyptemys insculpta). We conducted stationary and moving tests under a variety of device settings and field conditions. For stationary tests, accuracy was measured by calculating the 50% and 95% circular error probable (CEP) at each test location. The CEP is the radius of a circle centered at the true location which contains either 50% or 90% of locations. We also calculated angular dispersion of each dataset, a measure of the direction and concentration of locations. Moving tests were conducted at two sites where wood turtles occur in order to evaluate the GPS unit performance under expected field conditions. Location success was ≥ 95% for all tests, including moving tests, indicating strong potential for consistent performance in the field. Location accuracy was not affected by snapshot size, location interval, or canopy cover. The angular dispersion values calculated indicated little bias in any compass direction, although smaller datasets had greater bias. The 95% CEP for most tests was < 40 m, demonstrating feasibility for assessment of wood turtle movements and habitat use. Integrating use of a temperature sensor would allow for better determination of aquatic vs. terrestrial behavior. To increase accuracy of GPS datasets, data should be screened to identify and remove outliers, using prior knowledge of animal movement characteristics. The high accuracy and location success documented in our tests combined with low power consumption and high storage capacity demonstrates the potential of the G10 Ultralite as an effective animal tracking device.