Error in Telemetry Studies: Effects of Animal Movement on Triangulation

Abstract

We used Monte Carlo simulations to investigate the effects of movement on error of estimated locations derived from radio-telemetry triangulation of sequentially obtained bearings. Simulated movements of 0-534 m resulted in up to 10-fold increases in average location error but <10% decreases in location precision when observer-to-animal distances were <1,000 m. Location error and precision were minimally affected by censorship of poor locations with Chi-square goodness-of-fit tests. Location error caused by movement can only be eliminated by taking simultaneous bearings. J. WILDL. MANAGE. 54(3):506-510 Telemetry triangulation commonly used for obtaining location estimates of animals. The accuracy of a location estimate is a function of tower locations, the animal's location relative to the towers, and precision of the bearings from the tower to the animal (White and Garrott 1986:509), where towers refer to the antennas used by observers to obtain bearings. For triangulation from fixed antennas where bearings are obtained simultaneously, an has only 1 location relative to the antennas. However, many studies employ a single mobile antenna to sequentially obtain all bearings for a single location estimate. The time delay due to changing ' Present address: Alaska Fish and Wildlife Research Center, U.S. Fish and Wildlife Service, 1011 E. Tudor Road, Anchorage, AK 99503. This content downloaded from 157.55.39.116 on Sat, 11 Jun 2016 06:28:10 UTC All use subject to http://about.jstor.org/terms J. Wildl. Manage. 54(3):1990 MOVEMENT-INDUCED TELEMETRY ERRORn Schmutz and White 507 antenna locations allows for movement and, thus, error due to changes in the animal's position. These errors may decrease the ability to detect habitat selection (White and Garrott 1986) or may alter the interpretation of social interactions (Pyrah 1984, Andelt 1985). Our objective was to simulate the telemetry location process and to understand how movements might magnify telemetry location error. By examining movements simultaneously with other sources of location error, the relative importance of movements in obtaining accurate location estimates can be determined. We thank C. E. Braun, C. A. DeYoung, K. M. Giesen, N. T. Hobbs, J. K. Ringelman, D. G. Saltz, Y. Cohen, and 5 anonymous reviewers for comments on the manuscript. Our study was conducted while the senior author was receiving a graduate research assistantship from the Colorado Division of Wildlife.