Radio telemetry is a tool used to research wild animal species in the field in order to gain a thorough understanding of that population and its dynamics as well as to identify any potential threats to its survival. This information can then be used to formulate management plans for the long-term conservation of that species.
Baseline data like daily movements, home range size, use of home range, behaviour and diet are important for a thorough understanding of the species in question. This can in theory be done by following the animal in order to observe its movements and habits, but in practice this is likely to prove very difficult, particularly in areas with thick vegetation or where the animal is active at night (e.g. Lions or Spotted Hyena) or when dealing with a species with secretive habits. There is also the risk that the close proximity of humans could affect the animals behaviour resulting in an unrealistic outcome of the study or possibly having a negative affect on the study animal, like interfering with the hunting success in carnivores.
One of the most widely used method of gathering information about an animals movements is
the use of Radio Tracking (or to use the correct terminology, Radio Telemetry).
The idea is fairly simple - suitable study animals are fitted with radio collars
which incorporate a radio transmitter, which is set to transmit a signal at
regular intervals on a pre-set frequency, powered by a battery, which can last
up to three years. Very often the animal has to be tranquilised before the
collar can be fitted. Once the collar is activated by removing a magnet, the
researcher then fine tunes their receiver to the collar frequency by listening
to the quality of the signal received via the antenna attached to the receiver.
When the animal recovers from the anaesthetic it is free to move away.
When researcher is ready to track one of the animals that has been fitted with a radio collar, they tune their receiver in to the frequency that animal's collar is set to and listens for the signal. The receiver is equipped with an aerial which is designed to be directional - in other words the researcher has to point it in the right direction to pick up the best signal. By rotating the aerial and holding it in both vertical and horizontal positions, the researcher can identify which direction the animal is in. The exact position of the animal can be pinpointed through triangulation whereby the signal is located from two or different positions which are marked on a map and a line is drawn from each position in the direction of the compass bearing where the signal is strongest. The location of the animal corresponds to the point where the lines intercept. In the case of carnivores which are mostly active at night, they are located during their day time resting positions and at least 24 hours apart to ensure that location fixes are independent of each other.
In practice there are a number of factors that make this more difficult.
Firstly the animal could be moving which makes it hard for a single researcher to pinpoint its location - although the researcher can simply follow the strongest signal and then follow the direction of the strongest signal and stop to take additional readings at regular intervals - if the animal is stationary then they will keep travelling on their original heading, but if it is moving then they may need to change course after each reading to keep heading for the animal. Eventually they will locate the animal (assuming the researcher is able to travel slightly faster than the animal they are searching for). Alternatively they can work with a second researcher and both take reading from different locations and communicate by radio to discuss their locations and the direction in which they are getting a strong signal - this allows them to look on a map to see where the two signal readings cross which gives the animals location.
The clarity of the signal can be affected by the terrain. Mountains and rocks can block or even bounce a signal resulting in a false direction. Line of sight especially when tracking from an elevated position results in crisp clear reception.
Once the researcher gets close to the collared animal the antenna becomes less useful for location - the signal is so strong that whichever way the antenna is held the researcher still gets a good signal so they don't know the exact direction to the animal, just that its a short distance. In some areas this isn't a problem, but in areas with lots of trees, bushes or long grass the animal can be very close but still invisible.
Cheetah with its radio collar clearly visible
When searching for radio collared animals in a large study area, the most effective way to locate the animals quickly is to use an aircraft fitted with radio tracking equipment. Whereas tracking from the ground may give a range of one or two miles (depending on the terrain), tracking from the air has a much larger range - up to 30Km in some cases. When use of an aircraft is either not practical or is too expensive, climbing a hill to take the readings is also an effective way to boost the range.
Technology has moved on a long way from the early days of radio tracking. Originally collars constantly issued a regular signal using VHF radio. More modern VHF radio collars have a number of additional features.
Radio collars are available in a huge range of sizes to fit animals ranging in size from rodents to African elephants. They are made from a range of materials - typically leather or synthetic belting, but for small animals even a simple plastic cable-tie can be used to mount a radio transmitter.
Radio collars have even evolved to save the lives of some of the animals
wearing them. Greg Rasmussen of the
Painted Dog Project, worked with tracking collar supplier
Sirtrack to design a unique addition to
their collars. This addition is an anti-snare plate which consists of an
aluminium plate which runs along the base of the collar with 3 rows of rivets,
17 in total, protruding from the plate. If an animal wearing the
anti-snare plate is unfortunate to enter a snare, the rivets act as points to
break the wire and also prevent the wire cutting into the neck of the animal,
raising its chances of survival.
Many researchers are now using these anti-snare plates on collars without
transmitters, just to increase survival rates in areas where poaching is common.
Photo courtesy of Sirtrack.
A newer development is GPS collars. These use the Global Positioning System to record the animals exact location and store readings at pre-set intervals. When the researcher later recovers the collar the data can be downloaded and plotted on a computer giving detailed information about the animals movements during the period it was collared. By setting the interval between readings, the researcher is able to affect the lifespan of the collar - very frequent readings uses the battery power faster so the collar doesn't last as long, whereas long intervals between readings gives potentially less accurate data but the battery lasts longer.
Photo of a GPS collar (left) and radio collar (right)
Some collars can be programmed to drop off at a set time/date rather than the researcher having to dart the animal and remove the collar manually. Some collars also allow the researcher to send a signal to the collar which triggers the automatic release. To make the collar recovery easier, some GPS collars also include a VHF transmitter with its own power supply as this will normally last longer than the GPS battery and so the researcher is able to use the VHF signal to locate the collar either while it is still on the animal, or once it has dropped off. This can prove to be vital as some animals have been observed to pick up a collar that has automatically dropped off and to then run off into the distance, carrying it - subsequent location could prove almost impossible without the collar having a VHF transmitter. Some GPS collars also allow the data to be downloaded remotely, either by a radio link or in areas with GSM mobile phone coverage, by SMS text messages.
A big advantage of the GPS collars is that whereas most radio tracking is done during the day (when its possible to see the terrain clearly making it safe to drive), animals are often active at night, and a GPS collar records data day and night. It also allows the researcher to fit several collars and then not need to spend large amounts of time tracking the animals to build up the data - it can be simply downloaded at a later date.
The image below shows a map of part of the Brown Hyena Research project study area. A Brown Hyena was fitted with a GPS collar and set to take frequent readings. After several months the collar was retrieved and the data was downloaded onto a PC. The GPS position readings were then overlaid onto a map with each red dot representing a single GPS reading. The downloaded data provides a detailed picture of everywhere the Brown Hyena has been and it enables the research team to see where it spent most of its team but also to see that on two or three occasions it left its home range and travelled long distances to two locations - a source of fresh water and a seal colony. Because a lot of the Brown Hyenas activity takes place at night then the GPS collar provided data that daytime readings with a radio collar would not have revealed.
An alternative to GPS collars are satellite tracking collars which transmit a signal or data via the Argos satellites which collect, process and disseminate environmental data using the Doppler Shift method to work out the location of the transmitter fitted on to the wildlife). Typically latitude, longitude and altitude are transferred , but temperature and activity data can also be transferred depending on the settings chosen during manufacture. This system has been in use since 1978, when the Argos system went into service, and thousands of animals have been tracked worldwide using the Argos system.
Researchers are able to trace wildlife migration routes and movements on a 24 hour basis which was impossible with VHF alone. Often VHF transmitters are incorporated into the satellite tracking collar or package to assist with either pinpointing the animal or finding the PTT once it has dropped off the animal.
The Argos system collects data from Platform Terminal Transmitters (PTTs) and delivers this telemetry data to the user´s desktop.
The disadvantage of the Argos system is that it has ongoing costs to receive the data as well as the initial cost of the collars whereas GPS or VHF collars only have the initial purchase costs.
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Radio or GPS tracking is also used on creatures where a collar is not suitable, such as birds or turtles. In these cases different ways of attaching the device need to be used. In the case of birds, the radio or GPS unit must be extremely lightweight to avoid affecting the birds ability to fly and the units are usually attached by gluing them to the bird. The units will naturally fall off when the bird starts to moult. Similarly with turtles, gluing the unit on to the turtle's shell is the most effective way to mount the unit without causing discomfort to the turtle. Units used with turtles or other marine animals have to be waterproof and able to resist the corrosive effects of sea water.
In other cases an implant may be used if a collar or other external attachment is impractical or undesirable. This can either be subcutaneous (under the skin), or in the peritoneal cavity (under the muscle layer). As well as being used for visual reasons, implants can be used as part of studies to monitor the animals body temperature or heart rate. When Rhino are to be tracked, a popular method is to drill a hole in the tusk and mount the implant in the hole. The down side of implants is that they can suffer from a reduced range when compared to collars as the animals body will block some of the signal thus reducing its strength and range.
© Predator Conservation Trust.
