Definition

Telemetry (tele = distance, metry = measurement) refers to measuring from a distance. "Radio" telemetry refers specifically to telemetry in which information is transmitted over VHF radio waves. Although several aspects of an animal's biology can be measured remotely with telemetry, we use this tool specifically to measure a squirrel's position in space.

Components

There are three components to a radio telemetry system.:

1.A transmitter is worn by the animal subject. It transmits a pulsed signal (every 1.5 seconds) as a VHF radio wave. Squirrel transmitters weigh 4 grams and are worn around the neck.

2.A receiver receives the radio signal and translates it into something we can interpret such as an audible beep. The receiver can be tuned to receive specific radio frequencies within a broad range, thus one receiver can be used to identify and track multiple animals whose radio collars transmit at different frequencies.

3.An antenna amplifies the radio signal being received. A "directional" antenna receives the radio signal with different sensitivity (gain) depending on the orientation of the antenna - the beep is loud when the antenna pointed toward the animal, but becomes increasingly softer as the antenna turns away from the animal.

Techniques

In Squirrel Camp, we use radio telemetry primarily for radio tracking - following the radio signal until the animal is located visually. Starting at some distance from the squirrel, we travel in the direction in which the radio signal is strongest. As we get closer to the squirrel, the radio signal increases in strength, i.e. the beep gets louder, and we can reduce the sensitivity (gain) on the receiver for better sound resolution. We home in on the squirrel until we make visual contact. This gives us the squirrel's exact location in space, and allows us to observe its behavior at the time. Experienced researchers can locate squirrels in less than ten minutes with this technique.

Occasionally, we use triangulation to locate squirrels from a greater distance. Triangulation involves recording the direction from the observer to the squirrel as a compass bearing from two or more observer locations. These bearings are then plotted as lines on a map, which intersect at the animal's location. Unlike radio tracking which gives an exact location, triangulation involves some estimation error, but can be kept small by experienced researchers.

On foot in the boreal forest, we can detect the radio signals from squirrel radio collars from distances of about 300 meters. Antennas positioned higher can receive signals from greater distances. Common tactics to increase the range involve gaining elevation, and include climbing hills and trees, or when these are not available, standing on your vehicle.

Applications

Radio telemetry has many applications in wildlife biology. Telemetry-based analyses we conduct on the red squirrel project include:

Resource use - nest sites, feeding locations

Habitat selection - used sites chosen from among those available for use

Survival - Longevity, location and cause of death

Movement patterns - sequential locations of moving animals such as dispersing juveniles

Activity patterns - timing and duration of activity and sleep, nest use

Behavioral observation - focal sampling for determining diet, mating choices, caching behavior

Home range analysis - drawing polygons around a large set of mapped locations

-MCA