EFFECTS OF ANIMAL ACTIVITY ON GPS TELEMETRY LOCATION ATTEMPTS

Abstract

Interpretation of habitat use from GPS collar locations could be biased if the activity of animals wearing GPS collars affects the probability of obtaining a successful location. We tested for this bias with GPS location attempts made by collars deployed on free-ranging moose (Alces alces) in northern Minnesota, USA. We classified moose as being either inactive or active during each GPS location attempt based on activity counts recorded by the collar. Only 69% of GPS location attempts were successful while moose were active, compared to 88% of when moose were inactive. Moose activity reduced success of location attempts in both summer and winter. We also estimated the precision of GPS locations while collars were deployed on free-ranging moose. When moose were inactive 50% of 3-dimensional locations were within 5 m of the estimated location, and 95% were within 17 m of the estimated location. When moose were inactive, 50% of 2-dimensional locations were within 7 m of the estimated location, and 95% were within 26 m of the estimated location. Despite the bias induced by animal activity, GPS telemetry is the most precise method currently available to obtain locations of free-ranging large mammals such as moose. Sampling biases in GPS units resulting from animal activity should be accounted for when interpreting habitat use by free ranging animals.