Radio Telemetry

In the past, information about the biology, behavior, survival, and effects of the human footprint on the sage-grouse have been obtained observational studies that incorporated standard very high frequency (VHF) radio-telemetry. This technology allowed investigators to assess and evaluate habitat-use patterns, seasonal movement, and mortality by relocating sage-grouse that were marked with these radios. The very early sage-grouse radio-transmitters weighed more than 70 g (> 5% of an adult female’s mass or the weight of three Eisenhower silver dollars) and had relatively short battery lives. The weight of these early transmitters and how they were deployed on sage-grouse may have increased individual bird mortality risks. But by the late 1970s, improvements in transmitter technology resulted in radio-transmitters that weighed 25 g (2% or less of an adult female’s mass, weight of one silver Eisenhower dollar ) and batteries that lasted several months.

Throughout the 1970s and early 1980s, transmitters were attached to sage-grouse using variations of a backpack harness. Research in the early 1980s demonstrated that backpack harnesses also may increase a sage-grouse predation risks. Subsequently many biologists switched to a poncho-mounted transmitter. These transmitters were used on sage-grouse throughout much of the 1980s and early 1990s. The ponchos were custom fit to individual birds and the transmitter was attached to the poncho so that it would lie against the bird’s crop. During this time solar powered transmitters that included batteries were used with ponchos. By the mid 1990s, biologists adopted a battery-powered transmitter attached around the bird’s neck by a necklace consisting of plastic-coated cable. This necklace was lighter than a poncho and could be attached quickly to reduce the handling time for each bird. The per unit cost was approximately $200.

These standard radio-telemetry transmitters may have limitations if the research questions require more detailed knowledge of bird movements (i.e., exact and multiple daily locations) and behavioral responses to changes in the landscape. But the standard radio-telemetry (VHF) methodology has been largely preferred because of the higher costs associated with newer global positioning system (GPS) satellite telemetry technology (i.e., a single GPS radio-transmitter can cost several thousand dollars with additional costs associated with data downloads) and the increased weights.

Early GPS type radio-transmitters weighed >30 grams. They could be deployed using a leg-loop harness (i.e., rump mount) rather than a backpack harness. These GPS transmitters have several advantages over traditional VHF transmitters because they can collect multiple locations per day at pre-programmed times, reduce problems with on-the-ground access, eliminate observer disturbance of the bird. They also can provide real time data on survival, movements, habitat use, and timing of nest initiation. Solar-powered GPS transmitters must be mounted dorsally with exposure to the sun to ensure adequate battery recharge. Using this technique, researchers have successfully obtained hourly locations on sage-grouse throughout the year. This allows for concise documentation of seasonal habitat use, daily and seasonal movement patterns, nest initiation, foraging activities while incubating, and habitat use after hatching.

While initial costs associated with GPS transmitter technology are higher than conventional VHF transmitters, cost savings typically would accrue in longer duration studies in terms of personnel, time, study logistics, and a reduction in the number of VHF units deployed. However, there are some concerns that rump-mounted GPS transmitters may directly or indirectly reduce survival, rates of nest initiation, or movements of sage-grouse because of their similarity to backpack-style transmitters.