SREL Reprint #2692

Aerial telemetry accuracy in a forested landscape

Travis L. DeVault1, Warren L. Stephens2, Bradley D. Reinhart2, Olin E. Rhodes, Jr.3, and I. Lehr Brisbin, Jr.2

1Department of Forestry and Natural Resources, Purdue University, West Lafayette, IN 47907 U.S.A.
2Savannah River Ecology Laboratory, Drawer E, Aiken, SC 29802 U.S.A.
3Department of Forestry and Natural Resources, Purdue University, West Lafayette, IN 47907 U.S.A.

Introduction: Radiotelemetry is one of the more widely used tools for investigations of animal movements, home range size, habitat use, and survival. Radiotelemetric estimations of animal locations, however, are not without error. Bearing errors associated with ground-based triangulated estimates of radiotagged animals can be in excess of 20 degrees (Hupp and Ratti 1983, Garrott et al. 1986), and depending on the aim of the study, excessive error may preclude meaningful analyses of data (White and Garrott 1990). Some researchers have chosen to ignore the issue of error in telemetry data (see Hupp and Ratti 1983, Saltz 1994, Withey et al. 2001), but ultimately the value of telemetry data is severely diminished when the magnitude of error is not investigated.
Aerial tracking may be more desirable than ground-based methods in studies involving telemetry of wideranging birds and other highly mobile animals, or in dense forests where signal "bounce" may limit the effectiveness of ground-based telemetry (Gilmer et al. 1981, Marzluff et al. 1994). Aerial tracking allows researchers to avoid much of the potential error associated with ground-based tracking because fewer obstructions lie between the receiver and transmitter. However, aerial telemetry does not always provide "line of sight" radio fixes, especially in heavily forested landscapes. Although many studies have elucidated environmental factors contributing to bearing error from ground-based telemetry, no studies have documented how environmental factors influence conventional aerial telemetry accuracy.
In this study, we evaluated the accuracy, precision, and sources of error for an aerial telemetry protocol designed for investigations of home range size and movement patterns of raptors and other wide-ranging birds at a heavily forested site in South Carolina, U.S.A. At this site, ground-based telemetry for wide-ranging animals is impractical due to substantial forst cover and extensive roadless areas.

Keywords: aerial telemetry; geographic information system; radiotelemetry; telemetry error

SREL Reprint #2692

DeVault, T. L., W. L. Stephens, B. D. Reinhart, O. E. Rhodes, Jr., and I. L. Brisbin, Jr. 2003. Aerial telemetry accuracy in a forested landscape. Journal of Raptor Research 37:147-151.

This information was provided by the University of Georgia's Savannah River Ecology Laboratory (srel.uga.edu).