Northern Prairie Wildlife Research Center
Advances in the construction of attachment packages and batteries have reduced adverse impacts of radio-tagging. For example, researchers creatively minimized radio-tag visibility in the cases of leopard (Hamilton 1976) and farm cat (Macdonald and Apps 1978) telemetry studies by painting the radio collars to match each feline's coat color and pattern.
Improved technology and decreases in battery weight now allow complete transmitter packages weighing as little as 0.8-1.2 g to last 20-30 days (Samuel and Fuller 1996). Since weight is a primary concern in radio-tagging, advances such as this are significant to minimizing adverse effects.
When researchers were confronted with the problem of whip antennas on red-cockaded woodpeckers snagging in tree bark, a more flexible antenna was used to alleviate this (Nesbitt et al. 1982). Also, Boshoff et al. (1984) and Karl and Clout (1987) incorporated weaker materials into collars used on birds to allow the collar to break away should it become snagged or entangled.
Expandable break-away collars are another advance. They have also been used on black bears (Strathearn et al. 1984), young bobcats (Jackson et al. 1985), young mountain lions (Garcelon 1977), caribou calves (Adams et al. 1995), and elk calves (Singer et al. 1997). Several attachment methods have been modified to free the animal from the transmitter. For example, collars incorporating elastic (Amlaner et al. 1978; Hirons and Owen 1982) or cotton threads (Karl and Clout 1987) deteriorate, loosen over time, and eventually fall off. However, the time required before the collar is dropped can be highly variable (Samuel and Fuller 1990) and consideration should be given to the interim period when the collar is still attached but poorly fitting and possibly impeding movements or chaffing excessively.
Researchers have also used harnesses that automatically release the radio package after a predetermined period and thereby avoid the slow "wearing away" interim period (Makcay 1974; Jackson et al. 1985). Similarly, GPS collars have remote drop-off mechanisms (Mech et al. 1990), so the collar can be retrieved without having to recapture the animal (Merrill et al. 1998).
Trap-transmitters have been employed on large-carnivore traps to help minimize injuries and capture-related stress (Hayes 1982; Nolan et al. 1984). The signal from the transmitter (which is attached to the trap and monitored throughout the trapping) changes pulse rate when the trap has been activated. The altered signal alerts researchers, which allows them to reach the trapped animal more quickly; thus the animal has less time to injure itself by frantic escape attempts. Transmitters can also be used to remotely trigger a trap.
Special "capture collars" minimize stress during recaptures as animals are remotely darted without the immediate presence of the researcher and without being restrained (Mech et al. 1984, 1990, DelGiudice et al. 1990, Mech and Gese 1992). Researchers locate the animal via telemetry and then signal its collar to fire a dart containing drugs into the animal. The collars are also equipped with a back-up dart. The researchers then follow the signal until the animal is under the effects of the injected drugs. This technique minimizes stress for the animal during recaptures (DelGiudice et al. 1990).
White and Garrott (1990) made five recommendations for researchers when implementing a radio telemetry study; 1) use the lightest-weight transmitter package possible, 2) select an inconspicuous package especially when dealing with animals that rely on cryptic coloration, 3) test the transmitter packages on captive animals first in a variety of environmental settings, 4) wait one week before collecting data to use in analysis, and 5) avoid handling/instrumenting an animal during any critical life history period (especially reproductive periods). Amlaner (1978) suggested that researchers should strive to use minimal-weight transmitter packages and non-restrictive harnesses.
If researchers follow the above suggestions, the benefits of radio-tracking studies should outweigh the potential adverse effects, resulting in a greater chance of obtaining unbiased data and of minimizing adverse effects for the instrumented animal.