= Wildlife radio telemetry
<Wildlife radio telemetry> applies <animal radiotelemetry> to locating and monitoring free-living animals. In a conventional field setup, an attached <radio transmitter> emits a signal and the observer uses an <antenna> with a <radio receiver>. <Radio direction finding> estimates the direction toward the tag; repeated observations can then reveal movement and a <home range>.
An idealized geometric example shows why one direction does not locate the animal completely. In a flat map with coordinates measured in kilometres, an observer at $(0,0)$ obtains the bearing line $y=x$, while an observer at $(1,0)$ obtains $y=1-x$. Their intersection is $(0.5,0.5)$. A single bearing leaves a whole line of possible locations. In practice, angular error broadens the intersection, and nearly parallel bearing lines give poorly constrained positions.
A field location is also time-specific: combining directions taken far apart in time can be misleading if the animal moves between observations. The biological interpretation then requires more than drawing a line around fixes. A study of free-roaming domestic <cats> paired radio-based location measurements with activity sensors, illustrating how movement measurements can be combined with behaviour.<Home Range, Habitat Use, and Activity Patterns of Free-Roaming Domestic Cats by Jeff A. Horn and others>[Abstract and Introduction; radio-telemetry and collar activity study]{ref}
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