Northern Prairie Wildlife Research Center
The technique that has most revolutionized wildlife research, however, is radio-tracking, or wildlife telemetry. As we will discuss, the potential for learning new information with this technique is almost unlimited. On the other hand, the technique requires the live-capture of animals and usually the attachment of a collar or other device to them. It then usually requires someone to listen for a signal from the device periodically. This means people in the field in vehicles, aircraft, and on foot.
Despite the disturbance caused by radio-tracking wildlife, most national parks have recognized the benefits of the technique and hosted radio-tracking studies for many years; in some parks, hundreds of animals have been, or are, being studied, by radio-tracking. Consequently, some NPS staff have voiced concern about the actual or potential intrusiveness of radio-tracking studies. Ideally, such studies would still be done but with no intrusion or conflict with visitors.
Thus the NPS has sought to closely examine the wildlife radio-tracking technique so as to determine (1) if any less-intrusive methods could supply the same information, (2) what the full range of radio-tracking technology is in order to determine if the least-intrusive techniques are being used, and (3) whether future technological improvements might lead to less-intrusive techniques. The present review is the result.
Our approach will be to first present a simple overview of radio-tracking technology so the reader will be aware of the benefits, variety, cost, and availability of the technology, and the advantages and disadvantage of each type. We will also highlight the little-known, recent refinements that, if used, could reduce research intrusiveness.
Then we will examine the question of whether or when any less intrusive, non-radio-tracking techniques could supply the same information. Next we will discuss what future improvements may be on the horizon and suggest some that, if or when doable, would help reduce intrusion in national parks.
Last, we will present a detailed review of radio-tracking technology for readers who want a more complete understanding of the technique in question. This review will also allow administrators and scientists to determine whether the least-intrusive radio-tracking techniques are being used.
Radio-tracking is the technique of determining information about an animal through the use of radio signals from or to a device carried by the animal. "Telemetry" is the transmission of information through the atmosphere usually by radio waves, so radio-tracking involves telemetry, and there is much overlap between the two concepts.
The basic components of a radio-tracking system are (1) a transmitting subsystem consisting of a radio transmitter, a power source and a propagating antenna, and (2) a receiving subsystem including a "pick-up" antenna, a signal receiver with reception indicator (speaker and/or display) and a power source. Most radio tracking systems involve transmitters tuned to different frequencies (analogous to different AM/FM radio stations) that allow individual identification.
Three distinct types of radio-tracking are in use today: (1) very high frequency (VHF) radio tracking, (2) satellite tracking, and (3) Global Positioning System (GPS) tracking. VHF radio-tracking is the standard technique in use since 1963. An animal wearing a VHF transmitter can be tracked by a person on the ground or in the air with a special receiver and directional antenna.
Briefly, the advantages of VHF tracking are relatively low cost, reasonable accuracy for most purposes, and long life; disadvantages are that it is labor-intensive and can be weather-dependent if aircraft-based. Nevertheless, VHF radio-tracking is by far the most useful and versatile type of radio-tracking, for not only does it yield location data, but it also allows investigators to gather a variety of other types of information (Mech 1974, 1980, 1983).
Satellite tracking employs a much higher-powered transmitter attached to an animal. The signal is received by satellites and the animal's calculated location is sent to a researcher's computer. Satellite tracking requires a much higher initial cost and is much less accurate (mean accuracy = 480 meters [Fancy et al. 1989]) and, for most species, is shorter-lived than VHF systems.
If only animal locations and gross movements are of interest to a study, such as a dispersal path, satellite tracking is advantageous because it requires no personnel in the field once the tracking device is placed on the animal. It is especially useful for monitoring long-range movements. However, most wildlife studies also require a variety of other information that satellite tracking does not provide, including number of companions, individual productivity, behavior, and population size and trend. For carnivores, information about predatory habits, such as rates, location, species, age, sex, and condition of their kills, cannot be obtained by satellite tracking.
GPS tracking is based on a radio receiver (rather than a transmitter) in an animal's collar. The receiver picks up signals from a special set of satellites and uses an attached computer to calculate and store the animal's locations periodically (e.g. once/15 minutes, once per hour, etc.). Depending on collar weight, some GPS collars store the data and drop off the animal when expired to allow data retrieval; others transmit the data to another set of satellites that relay it to the researchers; and still others send the data on a programmed schedule (e.g., daily) to biologists who must be in the field to receive them.
GPS tracking also has high initial costs and at present is relatively short-lived and applicable to mammals the size of a wolf or larger, or to birds on which solar cells can be used. GPS tracking is highly accurate and especially suited to studies where intensive and frequent data (many locations/day) are needed or useful. Depending on several variables, GPS tracking may or may not require frequent field visits.
Three recent refinements in radio-tracking can reduce intrusiveness by researchers using the technique. The first is the ability to program radio-collars to transmit only at certain times ("duty cycling") rather than continually. This refinement can double or triple transmitter life, thus reducing or eliminating the need to recapture an animal for replacing an expired collar. For example, using duty cycling, batteries in elk collars could now last 8 years or more.
The second recent refinement is a reduction in weight of GPS collars, thus allowing them to be used on smaller species. Or by adding additional batteries to the reduced package, larger animals could be tracked longer.
Third, GPS transmitters powered by solar cells are now available for birds. This new availability will allow biologists to study many birds without having to venture into the field to determine each location.
Details about these three refinements can be found below in the detailed radio-tracking section.
The radio-tracking technique is so revolutionary (Mech 1983) that there is no other wildlife research technique that comes close to approximating its many benefits. For example, before radio-tracking, the study of animal movements depended on live-trapping and tagging animals and then hoping to recapture them somewhere else. A refinement was the use of visual markers such as color-coded collars that allowed observers to identify individuals from afar. The crudeness and biases inherent in this method are obvious, but the technique is the next best to radio-tracking for this kind of study.
Although new technology and scientist ingenuity do occasionally produce other new wildlife research techniques, none have come close to substituting for radio-tracking. Two new techniques bear mentioning because they are being much touted for their lack of invasiveness. They are the use of hairs plucked from free-ranging animals, and the use of scats, both for DNA analyses. Both techniques may be highly useful, but such use would only be for very specialized objectives. Both can tell presence/absence of a species and even minimum numbers present, and scat analyses may even yield a reasonably accurate population estimate (Kohn et al. 1999). However, doubts and cautions about the research promise of these non-invasive DNA techniques are still being aired (Taberlet et al. 1999, Garshelis 2001).
Population estimates of wolves are usually done by VHF radio-tracking and aerial observation. Therefore, conceivably if the sole or primary objective of a wolf radio-tracking project is to estimate the population, DNA analysis of scats could be a substitute. However, this technique has not been proven practical yet with wolves, although it is currently under study (Peterson, Mech, Vucetich, and Wayne in progress).
Although the scat analysis technique for censusing would be much less intrusive than radio-tracking, there are three major disadvantages: (1) the logistics of proper wolf scat collection for a population estimate throughout the area to be censused are highly challenging and would require considerable field effort, (2) lab analyses of scat-derived DNA are problematic (Taberlet et al. 1999). and (3) the scat technique would provide little of the complementary data that radio-tracking yields such as behavioral observations, mortality rates and causes, dispersal, and various other data depending on the amount and frequency of tracking time.
One of the most important improvements that could be made for all types of radio-tracking would be more efficient power sources, i.e. lighter, smaller batteries. This advance would allow any or all of the following: (1) longer life, (2) greater range, (3) lighter packages, (4) use of present radio-tracking devices on smaller animals. Such improvements would greatly facilitate VHF, satellite and GPS radio-tracking.
More efficient batteries that would prolong transmitter life, of course, would have to be accompanied by longer-lives of the other transmitter components. Although this is not a problem for periods of up to 4 years, it could become a problem if batteries allowed even longer life.
Most of the above advances would also translate into reduced intrusiveness through reduced live-trapping for re-collaring, or reduced in-field tracking. For example, for a given weight of a GPS collar, longer life would mean either a higher rate of location acquisition or a longer period of data collection. These advantages would allow more species to be tracked with GPS collars rather than VHF collars, thus reducing the need for in-field tracking time by biologists.
A second improvement would be a more efficient transmitting antenna. A more efficient antenna would reduce power requirements, thus translating to gains and advantages similar to those of a more powerful battery.
More efficient and longer-lived and more durable solar cells would be a third advance that could translate into less intrusiveness in radio-tracking. Currently, solar cells are useful in certain applications, especially with birds. However, with mammals, cells can be covered by fur, mud and debris. Longer-lived rechargeable batteries, which act as buffers for storing energy from solar cells, would allow longer total life of solar-powered transmitter packages. Thus they would also constitute a significant improvement.
Greater accuracy of satellite tracking would render this technique far more useable for wildlife research within national parks. Lower costs of satellite and GPS equipment would allow biologists to make greater use of those technologies rather than the more intrusive VHF tracking, at least for the specialized objectives they can help meet.
Neither leading electronics engineers in the wildlife radio-tracking field nor National Aeronautical and Space Administration (NASA) personnel consulted for this report have indicated that any technological breakthroughs are imminent that will revolutionize wildlife radio-tracking. Thus only incremental improvements can be expected for the foreseeable future.
Perhaps the next improvement will be the perfection of hydrogen fuel cells small enough to be used in animal radio-transmitters; theoretically they could yield longer life or lighter packages. A current estimate is that such cells might be available in 3-5 years (Hulbert 2001).
If satellite telemetry could be made far more accurate, it could at least save on personnel-days in the field in vehicles, on foot, or in the air. However, prospects are low for increased satellite-tracking accuracy soon. Consultation with manufacturers of satellite telemetry equipment confirms that the relatively low degree of accuracy of satellite systems is inherent in the basic position-finding methods used.
Of course, radio-tracking technology, like all other technology, will continue to improve with time, and costs will decrease. The high degree of competition among the many commercial companies (Appendix A) providing radio-tracking equipment guarantees that. However, even if all the improvements suggested above were made, they would only reduce, not eliminate, the basic intrusiveness of radio-tracking. Animals would still need to be caught, and they would still need to host transmitter packages, external or internal.
Therefore, the most that can be expected in the near term for minimizing intrusiveness of wildlife radio-tracking is for researchers to make use of the best, most appropriate, radio-tracking technology they can for reaching their objectives. Because that approach is already in the best interests of wildlife studies, most scientists are already using it.
However, improvements in technology are occurring rapidly, so some biologists may not be aware of them. Thus it is useful to review the radio-tracking technique and its latest improvements in more detail.