Radio Telemetry and Wildlife Tracking

Introduction to radio-telemetry and wildlife tracking

Photo: Brown bear released with TGW-3680 system. Courtesy: Telonics

The Interagency Grizzly Bear Study Team (IGBST) has been monitoring and radio-collaring bears in the Greater Yellowstone Ecosystem (GYE) since 1975. Over 950 individual bears have been radio-monitored. Each year, the goal of the team is to radio mark and monitor at least 25 female grizzly bears, additionally, using radio telemetry to monitor a proportionate number of male grizzlies. It is necessary to radio-mark bears as it provides crucial information in tracking key population parameters. Other metrics documented include age at first reproduction, average litter size, cub and yearling survival, how often females produce a litter, and causes of mortality. Estimating survival data amongst the different demographic groups is referred to as “known fate monitoring.” In combination with annual counts of females with cub-of-the-year, it allows for estimation of the grizzly bear population and bounds on sustainable mortality limits. By monitoring bears on an ever-increasing urban landscape, it also assists managers in evaluating activities and how they may impact bears going into the future.

Introduction: Research involving the use and implementation of radio telemetry in field ecology started in the early 1960s (Marshall et al. 1962; Cochran and Lord 1963). One of the first uses of radio telemetry in large carnivores was by Craighead et al. 1963 on Yellowstone grizzly bears. Researchers and scientists frequently use radio telemetry to study and explore various topics in carnivore biology (Fuller & Fuller, 2012).

There is a distinct difference between radio-tracking and telemetry. Radio-tracking is a technique used to determine information about an animal (location, movement, etc.) through radio signals (collar or transmitter fitted on the animal)(Fuller & Fuller 2012). Telemetry is the actual transmission of information through the atmosphere by radio waves; hence, radio-tracking directly involves telemetry (Mech & Barber 2002).

Radio-waves are categorized in spectral bands: Very High Frequency (VHF = 30-300 MHz) and Ultra High Frequency (UHF = 300-3000 MHz)(Fuller & Fuller 2012).Bandwidth refers to a specific range of frequencies. Tracking animals is made possible through the signal transmission from the transmitter to the receiver, estimating the individual location or relaying information on heart rate, motion, body temperature, etc. The ability to gather this information is revolutionary (Mech 1983), and current technology continues to get better. A vast amount of information would not be possible to obtain without the aid of radio-telemetry, given the wide range, and continuous movements of carnivores (Fuller & Fuller 2012).

Photo: Aerial telemetry flight. Courtesy: USGS/IGBST

Photo: Ground based telemetry using H-antenna. Courtesy: IGBST

Considerations & Potential effects on animals: Before deploying a transmitter on any animal, one should consider the potential effects it may have on the animal(s) involved (Murray and Fuller 2000; Withey et al. 2001; Fuller & Fuller 2012; Cochran 1972; Marks and Marks 1987; Vaughan and Morgan 1992). Field personnel must exercise careful consideration must when deciding on transmitter design and size. Most animals fitted with transmitters are captured and restrained, sometimes sedated (anesthesia)(Cattet et al. 2008; Mulcahy and Gardner 1999; Agren et al. 2000; Arnemo et al. 2006). Exacerbated behavioral or physiological stress may result from the capture and deployment of a transmitter, potentially compromising the health of the animal (sometimes fatal)(Birgham 1989), simultaneously affecting the integrity of the result. Animals sometimes display behavioral or energetic changes resulting from capture & handling. No data can genuinely prove that radio-collaring/tagging has no adverse effect on an animal (Mech & Barber 2002). Results demonstrated to date only demonstrate that no effect was detected when tested using the specified statistical power (White & Garrott 1990). On the contrary, more recent research has indicated that the effects of capture and collaring using current capture methods do not have long term implications, nor contribute to observable changes in body condition, reproduction or survival (Rode et al. 2014).

Photo: MOD-400-3 on urethane over butyl collar, with CAST-1 option. Courtesy: Telonics

Telemetry Systems - VHF & UHF: Most of the wildlife radio-telemetry has used VHF frequencies; however, satellite telemetry, with UHF frequencies and GPS Iridium are becoming increasingly popular (Fuller & Fuller 2012).

After the selection of the transmitter, a designation of frequency, signal pulse, signal strength, duration of the operation and the configuration/mass of the transmitting unit. The components of a radio-tracking system: transmitting subsystem (radio transmitter, power source, antenna), a receiving subsystem (receiving antenna, a signal receiver, reception indicator), and power source (Mech & Barber 2002). Specifically, a transmitter includes electrical circuitry, power source (battery), transmitting antenna, encapsulation (epoxy or resin), and material to attach to an animal (i.e., collar). The power source of a transmitter determines explicitly the duration for which the transmitter will operate (Fuller & Fuller 2012; Mech & Barber 2002). The signal power and operational life of the transmitter are notable tradeoffs with battery-powered telemetry because with batteries comes added weight. Current transmitting units utilize microprocessors and low power clocks to help conserve power. By adjusting the duty cycle, it may also minimize and conserve power (duty cycle refers to the ability to program, by turning on-or-off, transmissions at specific times) (Fuller & Fuller 2012).

Researchers frequently use collars to fit transmitters on mammals (Pouliquen et al. 1990), especially those with profound necks, large ears, and horns or antlers; these features help assist in the prevention of the collar from slipping over the head of the animal. For medium and large animals, the collar itself is typically made from leather, machine belting, braided nylon or synthetic dog collar material, and secured/reinforced by adjustable bolts, rivets, and buckles (Fuller & Fuller 2012). In some cases, the utilization of collars is not possible; one example is male polar bears, which undergo significant weight changes (Anderka and Angehrn 1992) and exhibit the ability to slip collars over their heads quickly. Specifically, when fitting and deploying radio-collars on grizzly bears, transmitter protection is essential. The manufacturer encapsulates the battery in resin or epoxy, also positioning the antenna between two layers of heavy collar material, which is common practice for animals that exhibit a high risk of breaking their antenna (Biggins et al. 2006; Schwartz and Arthur 1999; Loveridge and Macdonald 2002). In the case of grizzly bears, when fighting occurs, the neck and head region are the two areas targeted, which makes protecting the transmitter, battery, and antenna particularly essential to preserve functionality. Additionally, by reinforcing transmitters, batteries, and antennas, it also shields them from moisture and environmental factors, which could potentially damage or compromise the transmitter or collar functionality. In addition to the use of collars, researchers have also deployed ear-tag transmitters (Servheen et al. 1981) and adhesive transmitters (Anderka 1987) on bears.

In accompaniment to transmitters, there are a variety of sensors that are made available from a handful of manufacturers. Some sensors can detect body movement (Garshelis et al. 1982; Gervasi et al. 2006; Fuller & Fuller 2012), while others can detect temperature, activity, body position. Just like in smartphones, collars can use tilt switches to report the animal’s body posture (slow or fast pulse) (Theuerkauf and Jedrzejewski 2002). The utilization of accelerometers allows 3D motion sensing (Kappeler and Erkert, 2003; Moll et al., 2007). Personnel may determine activity from a given animal through changes in both radio signal strength and consistency (Weir and Corbould 2007); this also means that mortality can be detected through a lack of movement as well (Hass and Valenzuela 2002; Kamler and Gipson 2004; Mills et al. 2008). Some sensors can reset the pulse rate if the transmitter begins to move again (for example, denning bears), or programmed to remain in mortality mode for a specified period (Fuller & Fuller 2012).

Photo: This is a TGW-4570 Iridium/GPS collar manufactured by Telonics. This particular model is the most commonly used GPS on grizzly bears in the Yellowstone Ecosystem currently. This collar was purchased with grant money during spring 2019 for instructional purposes and demonstrations. Notice the white cotton spacer, and black commanded-release (CR) mechanism. Courtesy: Tyler Brasington

Photo: Torn collar spacer on an Iridium GPS collar during 2019. This spacer failed after only three months of deployment. Spacers are used as a back-up to commanded-release (CR) systems. Courtesy: Tyler Brasington

Data Storage & Options: Many may be asking where is all this locational, movement, and activity data stored? There are several options for how we can log and store data. Current options allow for store-on-board (SOB), which allows all information and data to be logged and stored on the transmitting unit, available for later download to a receiver system through radio transmissions. The other option is to recover the transmitter once it has been dropped or cast from the marked animal. It is also important to realize that telemetry units can be refurbished and reused (Fuller & Fuller, 2012). Other units do not have the SOB capability; this requires a manual fix location to be obtained (more fieldwork). Additionally, with GPS and satellite technology used more frequently, this allows the relay of information in real-time to scientists behind a desk (the frequency and amount of information relayed is determined, as previously mentioned by duty cycle).

Receiving systems: VHF receiving systems for wildlife telemetry includes a radio receiver, antenna, cables to connect the antenna to the receiver, and additional accessories (headphones, counters, decoders, and recording devices)(Fuller & Fuller 2012). Manual receivers can generally operate within bandwidths of 50-200 kHz, and use between 5-20 frequencies (Fuller & Fuller 2012). Programmable receivers are also an option for wildlife professionals and are incredibly beneficial when there are multiple transmitters in a given area (i.e., a survey from aircraft). In some cases, personnel may program a receiver so that it can record signals automatically and unattended (Fuller & Fuller 2012). Receiving antennas take form with a few different designs. There are omnidirectional, loop, Adcock/H antenna, yagi, and null-peak system. The omnidirectional antenna is also referred to as a “whip” and has a uniform 360-degree reception pattern, with reasonably low gain. These antennas are easily configured for vehicles and aircraft and generally used to detect presence over the location. Directional receiving antennas, in contrast, have a three-dimensional pattern, oriented by the element(s) of the antenna (Fuller & Fuller 2012). Making the antenna more directional will increase gain; a directional antenna will detect the most reliable signal when directed towards the signal origin. Elevation plays a role in transmitting and receiving antennas; the higher the elevation generally increase the reception range. That is not to say that terrain, vegetation, buildings will not block or cause interference with the signal transmission (Fuller & Fuller 2012).

Field Procedures: Personnel may maximize radio-telemetry locational accuracy and precision through appropriate training, and consistent procedures (White and Garrott 1990; Nams and Boutin 1991; Withey et al. 2001). There are several methods and techniques for locating radio-marked individuals. These include triangulation & homing. The method of triangulation involves obtaining two signal bearings from different locations, preferably at 90 degrees to one another, where the two bearings intersect is the estimated location of the animal. Generally, three or four bearings produces better results. When more than two bearings are involved, the bearings form an area called an “error polygon,” which contains the animals’ location (Heezen and Tester 1967; White and Garrott 1990). The benefit to triangulation is that it locates the individual animal with very little disturbance (Mech 1983); however, the further away, the larger the error (Mech 1983). Homing refers to the process of following a signal based on the greatest strength. As the individual researcher closes in on an animal’s location, the gain must be adjusted and reduced in order to better identify the direction of the signal. The researcher continually proceeds forward, following the strongest signal, gradually decreasing gain until the animal is in sight or visible, or until sufficiently near to estimate location (Mech 1983).

Photo: Early Argos transmitter attached to a brown bear in Alaska. Coutesy: Alaska Department of Fish & Game/Telonics

Satellite telemetry: The utilization of satellite telemetry permits remote tracking of animals across most places on earth, using the Argos system. The Argos system first became available in the 1980s and is still used to date (Harris et al. 1990). Early systems used NIMBUS satellites (Kolz et al. 1980; Schweinsburg and Lee 1982; Timko and Kolz 1982). Satellite telemetry was first implemented and utilized to track animals in the early 1970s (Buechner et al. 1971) but was only useful for large animals like bears (Craighead et al. 1971) and elk (Craighead et al. 1972; Lentfer and DeMaster 1982).

Satellite telemetry uses a platform transmitter terminal (PTT), which is fixed and attached to the animal. The PTT sends a UHF signal to satellites, then location is calculated based on the Doppler effect, and then relay the information to receiving sites on the ground. The main methods to attach PTTs include collars, harnesses, subdermal anchoring, harpooning with floats, or fur bonding (Taillade 1992).

These transmitters are typically programmed to transmit signals every 50-90 seconds, exhibiting a pulse width of roughly 0.33 seconds (Howey 1992; Samuel and Fuller 1996). When satellites pass overhead of the animal, there is a 10-12 minute window of time during which the satellite obtains the transmitter signal; it is essential to note that two satellites are necessary to obtain location information (Taillade 1992). The PTTs must hold enough power to communicate and transmit signals to satellites, which orbit between 800-4000 km away (Howey 1992). In order to accomplish this, the power ranges between 250 mW to 2W; this is in comparison to a traditional VHF transmitter, which has about 10 mW of power). A typical PTT collar requires 3 D-cell batteries, which last anywhere between 3-12 months, depending on how the duty cycle is programmed. To maximize the life of the collar, some researchers may adjust to turn on once every three days; this would yield three times the average life of a PTT transmitting every day (Mech & Barber 2002). The distribution of processed data goes to researchers and scientists in various formats, including internet access (for data received about 4 hours previously)(Fuller & Fuller 2012).

Photo: TAW-4210-3 "Argos-only" model on a butyl collar with CAST-4 option. Courtesy: Telonics

Satellite telemetry is less accurate than traditional VHF or GPS tracking. Satellite telemetry reports locations whose accuracy varies from 150 m to several kilometers (Keating et al. 1991).One study even found (Fancy et al. 1989) that 90% of satellite-based locations estimated to be within 900m of the known location, with an average error of 480 m.

Also, satellite telemetry can be viewed as both expensive and economical, depending mainly on the use and situation. The cost of one PTT unit generally ranges from 3,000-4,000 dollars. This price sits about 10-20 times the initial cost of a VHF transmitter (White and Garrott 1990). If the PTT can be retrieved, it typically costs $150-300 to refurbish. In addition to the initial transmitter cost, data acquisition, and processing cost $90-260/ month per animal (Wilson et al. 1992). Satellite-based transmitter deployment can be more cost-effective in certain situations (Craighead, 1987; Harrington et al. 1987; Fancy et al. 1989). For example, Fancy (1989) performed a five-year study, with ten animals, one location per day. This study yielded results, on a cost/data-point basis, that conventional VHF would be 43 times more expensive than satellite telemetry.

Global Positioning System (GPS) Telemetry: Global satellite coverage for military purposes was first developed by the United States Department of Defense (DoD) in 1973. In 1993, GPS technology reached operational capacity when the 24th satellite launched into orbit (Rodgers et al. 1996; Tomkiewicz 1996).

GPS telemetry is not to be confused with satellite telemetry. With satellite systems, the animals PTT is the transmitter, which sends information to the satellite receivers, further relaying this information to a recording/receiving station on earth. GPS telemetry uses a different set of satellites, which function as transmitters while the animals unit acts as the receiver. The signal information is then used by the unit to calculate its location based on current positions of satellites and the time taken for the signal sent from each satellite to reach the animal unit (Mech & Barber 2002). The animal unit stores the locational data for retrieval or remote downloading.

Photo: GPS Store-on-board models TGW-4000-4 and TGW-4502-3 on collars, and TGW-4100-2. Courtesy: Telonics

Photo: GPS/Iridium collars (TGW-4170-4, 4270-4, 4470-4, 4570-4, and 4670-4). Courtesy: Telonics

There are always at least four satellites available from any position on earth; each satellite orbits approximately every 12 hours. This presence also allows 3D-position acquisition based on four variables (latitude, longitude, altitude, time/receiver clock bias)(Mech & Barber 2002).

Lotek Engineering Inc. introduced the first GPS location system, the GPS_1000, during 1994. Since the first introduction, size has reduced, longevity has increased, and data storage and retrieval have drastically improved. The standard GPS collar consists of a GPS receiver and antenna, and a VHF beacon for locational backup and system verification, control hardware, and power supply (battery) (Rodgers et al. 1996; Mech & Barber 2002; Fuller & Fuller 2012). The biggest issue faced with GPS collars is their batteries. The most considerable drain and strain on a GPS battery are when the system continually searches for satellite signals to acquire a location fix (Mech & Barber 2002). Search time is a critical component in the longevity of the GPS collar; typical location acquisition may occur within 204 minutes due to canopy cover and topography of the region. Televilt has produced a GPS collar (POSREC-Science) that can obtain and locational fix within 10 seconds under ideal circumstances.

There are several other additions and advances to GPS technology for collars, and monitoring wildlife. These include indicators of time-in-mortality, commanded release (automatic drop off mechanisms), field-replaceable batteries, temperature and activity sensors, and remote two-way communication. Drop-off mechanisms, or known as “commanded release,” are mechanisms, make it possible for researchers to retrieve the collar without having to recapture the individual. Remote two-way communication also is notably beneficial because it allows researchers to minimize contact with the animal and make programmable adjustments (Mech & Barber 2002).

Photo: TGW-4600 collar system deployed on a brown bear sow. South Baranof Island, Port Armstrong. Courtesy: Telonics

Photo: 2005 - Gobi bear wearing a TGW-3481 GPS/ARGOS transmitter. (Courtesy: Gobi Bear Project/Telonics)

Data Storage for GPS systems: There are three main methods for data retrieval from GPS systems; data stored-on-board (SOB), data downloaded to a portable receiver, and data relayed by satellite.

Typically the cost of a GPS collar ranges from $3,000-4,500, about ten times the cost of a VHF collar for medium-sized animals (Merrill et al. 1998). A complete ‘start-up’ package for one animal fitted with a remote-downloading GPS collar costs roughly $10,500; this estimate includes a receiver at the cost of approximately $5,000, software with supporting cables for $2,000, and a collar with a drop-off or commanded-release mechanism and one extra battery for field replacement for $3,500. Any additional collars deployed after will be less of an investment, as one receiver can cover multiple frequencies and collars. GPS collars are also reusable and can be sent back to the manufacturer for refurbishment. Generally, a replacement commanded-release mechanism costs ~$275-300 and batteries for ~$187-200.

The initial investment and sometimes overall cost, while much more than traditional VHF systems, does not necessarily mean that GPS technology for the use in wildlife tracking, is less economical. Consider the comparison of cost/location as opposed to cost/animal. In this case, GPS collars can sometimes be less expensive and also save on personnel costs since studies may be less labor-intensive.

Figure: Screenshot Telonics Data Report from a GPS transmitter imported to worksheet within Microsoft Excel. This is a general depiction of how data is displayed after being imported. (Courtesy: Tyler Brasington)

Works Cited:

Ågren, E. O., Nordenberg, L., & Mörner, T. (2000). Surgical implantation of radiotelemetry transmitters in European badgers (Meles meles). Journal of Zoo and Wildlife Medicine, 31(1), 52-55.
Anderka, F. W. (1987). Radiotelemetry techniques for furbearers. In M. Novak, J. A. Baker, M. E. Obbard, and B. Malloch, eds. Wild furbearer management and conservation in North America. Ont. Minist. Nat. Resour., Tornoto. Pp. 216- 227.
Anderka, F. W., Angehrn, P. (1992). Transmitter attachment methods. In I. G. Priede and S. M. Swift, eds. Wildlife Telemetry Remote Monitoring and Tracking of Animals. Ellis Horwood, New York, N.Y. Pp. 135-146.
Arnemo, J. M., Ahlqvist, P., Andersen, R., Berntsen, F., Ericsson, G., Odden, J., ... & Swenson, J. E. (2006). Risk of capture-related mortality in large free-ranging mammals: experiences from Scandinavia. Wildlife Biology, 12(1), 109-113.
Beuchner, H. K., Craighead, Jr., F. C., Craighead, J. J., Cote, C. E. (1971). Satellites for research on free-roaming animals. BioScience. 21:1201-1205.
Biggins, D. E., Godbey, J. L., Miller, B. J., & Hanebury, L. R. (2006). Radio telemetry for black-footed ferret research and monitoring. Recovery of the black-footed ferret—progress and continuing challenges, 175-189.
Birgham, R. M. (1989). Effects of radio-transmitters on the foraging behavior of barn swallows. Wilson Bull. 101:505-506.
Cattet, M., Boulanger, J., Stenhouse, G., Powell, R. A., & Reynolds-Hogland, M. J. (2008). An evaluation of long-term capture effects in ursids: implications for wildlife welfare and research. Journal of Mammalogy, 89(4), 973-990.
Cochran, W. W. (1972). Long-distance tracking of birds. In S. R. Galler, K. Schmidt-Koening, G. J. Jacobs, and R. E. Belleville, eds. Animal orientation and navigation. NASA SP-262. U.S. Gov. Printing Off., Washington, D.C. Pp. 39-59.
Cochran, W. W., Lord, Jr., R. D. (1963). A radio-tracking system for wild animals. J. Wldl. Manage. 27:9-24.
Craighead, F. C., Craighead, J. J., & Davies, R. S. (1963). Radiotracking of grizzly bears. Pergamon Press.
Craighead, J. J, Craighead, D. J. (1987). Tracking caribou using satellite telemetry. Natl. Geogr. Res. 3:462-479.
Craighead, J. J., Craighead, Jr., F. C., Varney, J. R., Cote, C. E. (1971). Satellite monitoring of black bears. BioScience. 21:1206-1212.
Craighead, Jr., F. C., Craighead, J. J., Cote, C. E., Buechner, H. K. (1972). Satellite and ground radio tracking of elk. In S. Galler et al. Animal Orientation and Navigation. NASA, Washington, D.C. Pp. 99-111.
Fancy, S. G., Pank, L. F., Whitten, K. R., Regelin, W. L. (1989). Seasonal movements of caribou in arctic Alaska as determined by satellite. Can J. Zool. 67:644-650.
Fuller, M. R., & Fuller, T. K. (2012). Radio-telemetry equipment and applications for carnivores. Carnivore ecology and conservation: a handbook of techniques. Oxford University Press, Oxford, 152-168.
Garshelis, D. L., Quigley, H. B., Villarrubia, C. R., & Pelton, M. R. (1982). Assessment of telemetric motion sensors for studies of activity. Canadian Journal of Zoology, 60(8), 1800-1805.
Gervasi, V., Brunberg, S., & Swenson, J. E. (2006). An individual‐based method to measure animal activity levels: a test on brown bears. Wildlife Society Bulletin, 34(5), 1314-1319.
GPS collars on wolves and white-tailed deer. Wildl. Soc. Bull. 26(4):830-835.
Harrington, F. H., Veitch, A. N., Luttich, S. N. (1987). Tracking barren-ground and woodland caribou by satellite: the more the need for PTTs, the better they work. In Proc. Argos Users Conf., Service Argos, Greenbelt, MD. Pp. 221-242.
Harris, R. B., Fancy, S. G., Douglas, D. C., Garner, G. W., Amstrup, S. C., McCabe, T. R., Pank, L. F. (1990). Tracking wildlife by satellite: current systems and performance. U.S. Fish Wildl. Serv., Fish Wildl. Tech. Rep. 30. pp. 52
Hass, C. C., & Valenzuela, D. (2002). Anti-predator benefits of group living in white-nosed coatis (Nasua narica). Behavioral Ecology and Sociobiology, 51(6), 570-578.
Heezen, K. L., Tester, J. R. (1967). Evaluation of radio-tracking by tiangulation with special reference to deer movements. Journal of Wildlife Managment 31:124-141.
Howey, P. W. (1992). Tracking of birds by satellite. In I. G. Priede and S. M. Swift, eds. Wildlife Telemetry Remote Monitoring and Tracking of Animals. Ellis Horwood, New York, NY. Pp. 177-184.
Kamler, J. F., & Gipson, P. S. (2004). Survival and cause-specific mortality among furbearers in a protected area. The American midland naturalist, 151(1), 27-34.
Kappeler, P. M., & Erkert, H. G. (2003). On the move around the clock: Correlates and determinants of cathemeral activity in wild red fronted lemurs (Eulemur fulvus rufus). Behavioral Ecology and Sociobiology, 54(4), 359–369.
Keating, K. A., Brewster, W. G., Key, C. H. (1991). Satellite telemetry: performance of animal-tracking systems. J. Wildl. Manage. 55:160-171.
Kolz, A. L., Lentfer, J. W., Fallek, H. G. (1980). Satellite Radio Tracking of Polar Bears Instrumented in Alaska. In C.J. Amlaner, Jr. & D. W. MacDonald, eds. A Handbook on Biotelemetry and Radio Tracking. Pergamon Press, Oxford, pp. 743-752.
Lentfer, J. W., DeMaster, D. (1982). Satellite radio tracking of polar bears. In C. Cote, R. Taylor, and E. Gilbert, eds. Nimbus-6 random access measurement system applications experiments. NASA SP-457, Washington, D.C. Pp. 52-53.
Loveridge, A. J., & Macdonald, D. W. (2002). Habitat ecology of two sympatric species of jackals in Zimbabwe. Journal of Mammalogy, 83(2), 599-607.
Marks, J. S., Marks, V. S. (1987). Influence of radio collars on survival of sharp-tailed grouse. J. Wild. Manage. 51:468-471.
Marshall, W. H., Gullion, G. W., Schwab, R. G. (1962). Early summer activities of porcupines as determined by radio-positioning techniques. Journal of Wildlife Management 26:75–79.
Mech, L. D. (1983). A Handbook Of Animal Radio-tracking. Univ. of Minn. Press, Mpls. 108pp.
Mech, L. D., & Barber, S. M. (2002). A critique of wildlife radio-tracking and its use in national parks. Northern Prairie Wildlife Research Center.
Merrill, S. B., Adams, L. G., Nelson, M. E., Mech, L. D. (1998). Testing releasable
mice, Mus domesticus. Can. J. Zool. 63:1607-1609.
Mills, K. J., Patterson, B. R., & Murray, D. L. (2008). Direct estimation of early survival and movements in eastern wolf pups. The Journal of Wildlife Management, 72(4), 949-954.
Moll, R. J., Millspaugh, J. J., Beringer, J., Sartwell, J., & He, Z. (2007). A new ‘view’of ecology and conservation through animal-borne video systems. Trends in ecology & evolution, 22(12), 660-668.
Mulcahy, D. M., & Garner, G. (1999). Subcutaneous implantation of satellite transmitters with percutaneous antennae into male polar bears (Ursus maritimus). Journal of Zoo and Wildlife Medicine, 510-515.
Murray, D. L., Fuller, M. R. (2000). Effects of marking ion the life history patterns of vertebrates. Pp. 15-64, In: Research Techniques in Ethology and Animal Ecology (L. Boitani and T. Fuller, eds.). Columbia University Press, New York
Nams, V. O., & Boutin, S. (1991). What is wrong with error polygons?. The Journal of wildlife management, 172-176.
Pouliquen, O., Leishman, M., Redhead, T. D. (1990). Effects of radio collars on wild
Rode, K. D., Pagano, A. M., Bromaghin, J. F., Atwood, T. C., Durner, G. M., Simac, K. S., & Amstrup, S. C. (2015). Effects of capturing and collaring on polar bears: findings from long-term research on the southern Beaufort Sea population. Wildlife Research, 41(4), 311-322.
Rodgers, A. R., Rempel, R. S., Abraham, K. F. (1996). A GPS-based telemetry system. Wildl. Soc. Bull. 24(3): 559-566.
Samuel, M. D., Fuller, M. R. (1996). Wildlife Radiotelemetry. In T. A. Bookhout, ed. Research and Management Techniques for Wildlife and Habitats, 5th ed., rev. The Wildlife Society, Bethesda, MD. Pp. 370-418.
Schwartz, C. C., & Arthur, S. M. (1999). Radiotracking large wilderness mammals: integration of GPS and Argos technology. Ursus, 261-273.
Schweinsburg, R. E., Lee, L. J. (1982). Movement of four satellite-monitored polar bears in Lancaster Sound, Northwest Territories. Arctic. 35:504-511.
Servheen, C., Their, T. T., Jonkel, C. J., Beaty, D. (1981). An ear-mounted transmitter for bears. Wildl. Soc. Bull. 9:56-57.
Taillade, M. (1992). Animal tracking by satellite. In I. M. Priede and S. M. Swift, eds. Wildlife Telemetry Remote Monitoring and Tracking of Animals. Ellis Horwood, New York, NY. Pp. 149-160.
Theuerkauf, J., Jedrzejewski, W. (2002). Accuracy of radiotelemetry to estimate wolf actilit) and locations. Joumal of wildlile Managemcnt 66:lJ59 86,1
Timko, R. E., Kolz, A. L. (1982). Satellite sea turtle tracking. Mar. Fish. Rev. 44:19-24.
Tomkiewicz, S. (1996). GPS Application for Wildlife – A Review. Telonics Quarterly. 9(1): Spring and Summer.
Vaughan, M. R., Morgan, J. T. (1992). Effect of radio transmitter packages on wild turkey roosting behavior. Proc. Int. Eur. Conf. Wild. Telem. 4:628-632.
Weir, R. D., & Corbould, F. B. (2007). Factors affecting diurnal activity of fishers in north-central British Columbia. Journal of Mammalogy, 88(6), 1508-1514.
White, G. C., Garrott, R. A. (1990). Analysis of Wildlife Radio-Tracking Data. Academic Press, Inc., San Diego.
Wilson, R. P., Ducamp, J. J., Rees, W. G., Culik, B. M., Niekamp, K. (1992). Estimation of location: global coverage using light intensity. In I. G. Priede and S. M. Swift, eds. Wildlife Telemetry Remote Monitoring and Tracking of Animals. Ellis Horwood, New York, NY. Pp. 131-134.
Withey, J. C., Bloxton, T. D., Marzluff, J. M. (2001). Effects of tagging and location error in wildlife telemetry studies. Pp. 43-75, In: Radio Tracking and Animal Populations (J. J. Millspaugh andJ. M. Marzluff, eds.). Academic Press, San Diego.