Wildlife Telemetry
Wildlife telemetry is a method of ecological research for recording and tracking wild animals using high-frequency transmitters . With the help of wild animal telemetry, knowledge about the migratory behavior of migratory animal species can be obtained and knowledge about the ecology and habitat preferences of individual species can be determined. With the help of this data, measures to protect species and nature can be taken.
history
Among the animals there are a number of so-called " globetrotters ". Big birds like storks and geese or mammals like polar bears and whales are known. In addition, fish, butterflies and a number of other animals also seek out habitats and feeding areas that are far apart over the course of a year.
These animals were tracked using receivers and directional antennas on foot, by car, ship or plane. "Radiotracking" has been used since the late 1960s to research wild animals. The technical development in the manufacture of components towards integrated circuits and the now common semiconductor technology was essential . This made an increasing miniaturization of the transmitters possible. Today even small animals such as butterflies can be equipped with transmitters. Another factor was the increasing efficiency (battery and power consumption) of the transmitters.
A new possibility of global surveillance opened up in 1957 with the Russian Sputnik I satellite . Scientists at the American Johns Hopkins University noticed that the frequency of the received radio signals changed significantly depending on whether the artificial satellite was approaching or moving away from a receiving station. They used this so-called Doppler effect to calculate the position of the satellite on its orbit. Conversely, it had to be possible for an orbiting satellite to locate the location of a transmitter on earth. This idea was first taken up by the military to locate warships on the oceans. In 1978 the civil ARGOS system went into operation. Since then, in addition to determining the position of ships, containers and trucks, it has also been used for global observation of wild animals.
Wild animal telemetry began with a study published in Science magazine in 1966 by the American biologist Gerald Kooyman, who was the first researcher to use technical assistance to record detailed behavioral data of a diving animal.
methodology
The methods that are used to determine an animal's position today are essentially radio direction finding using triangulation (first described by Heezen & Tester 1967), homing-in from an aircraft or from the ground (first described by Hoskinson 1976) and the transmission of transmitter signals to satellites (first described by Harris et al. 1990).
With the expansion of the technical possibilities, more complex signals are now also being transmitted, for example the position data of a GPS receiver, so that a direct bearing is no longer necessary. In the meantime, physiological data (heart rate, body temperature, etc.) of the animal, some of which are recorded with data loggers , are also transmitted directly.
In order to be able to “transmit” animals, they are either provided with a transmitter after birth or caught for it. Depending on the species, the animals are caught using traps or Japanese nets (birds and bats). Larger mammals can also be immobilized with narcotics. The aim of all embedding measures is to keep the time it takes to put on the transmitter as short as possible in order to save the animals unnecessary stress. In the case of birds and flying mammals, the transmitters are usually glued to the dorsal fur (in bats) or dorsal plumage (in birds) with a medical skin adhesive at the level of the shoulder blades. Most of the time, the transmitters fall off by themselves after a certain period of time.
So-called dart transmitters are transmitters that are implemented in stunning projectiles. On the one hand, they make it easier to find the immobilized animal and, on the other hand, misdirected projectiles can be found again. The sedative can be secured again and accidents are avoided.
Triangulation
With the triangulation, the whereabouts of the animal is determined using cross bearings . Triangulation is therefore subject to a series of errors, since the localization is based on a series of azimuths . Errors of 100 to 200 m are typical.
Near-field telemetry is usually used in ecology, but it will be replaced by satellite-based technology in the next few years.
Homing-in
With homing-in, the location of the animal is searched for directly, similar to homing in aviation , using serial bearings. However, this often results in a certain error in the interpretation of the map, in particular in the case of flight bearings. The accuracy of all direct telemetry methods is very different and depends, among other things, on the topography.
Satellite channels
Localizations with the Argos satellite system can usually be found within a circle of 1 to 3 km around the transmitter. The system works in the L-band (401.650 MHz ± 30 kHz). Several satellites pick up the signals from the transmitters and forward the signals to ground stations. The position of the transmitter is calculated there. The heart of the ARGOS system are special transceivers with which some weather satellites are equipped. They circle the earth fourteen times a day on polar orbits at an altitude of 850 kilometers. In Europe, the ARGOS data is processed by the CLS (Collecte Localization Satellites) in Toulouse . From there, the users receive the coordinates of the transmitter they are using. The transmitters for the system are relatively large, but are also suitable for animals with long migration routes, such as marine mammals .
Combined data logger and transmitter
As an alternative to direct bearing, data can now also be transmitted via telemetry. The technical advancement in the field of transmission technology and satellite positioning makes it possible to send stored position data. GPS data loggers (store-on-board recording devices) with powerful two-stage transmitters can store up to 260,000 recordings and transmit the stored data using VHF transmitters. This allows very precise movement profiles of animals to be created. Although a potential accuracy of significantly <1 m is possible, in the wild biological use of GPS units in 50 percent of the cases only an accuracy of 40 m is achieved and 100 m in 95 percent of the cases.
Video telemetry
With the miniaturization of video cameras, this technology is also used in telemetry. Sharks , seals , whales and sea turtles have already been equipped with cameras. The so-called " Crittercam ", a camera with a recorder in a waterproof housing, is glued to the animal's skin with a plastic holder. In the narrower sense, this is not a question of telemetry, because the data to be evaluated are not transmitted at high frequencies. The dives of the animals can be followed, and you can see where the different species look for food, what they eat and what their daily routine looks like. After a programmed time, the camera releases from the animal and can be located by radio direction finding. The recordings can then be evaluated.
evaluation
In the meantime, special software is available for the data from wild animal telemetry and the data obtained are usually transferred to geographic information systems. The data is often incorporated into models .
In practice, the points targeted by conventional telemetry are corrected by an error ellipse . Various methods are used to further evaluate the ecological data such as the home range of an animal , the most common being the minimum convex polygon. Further evaluations are usually carried out using multivariate methods .
Legal
Wild animals are caught and temporarily deprived of their freedom to broadcast. In Germany, this is only permitted with special permits from nature conservation authorities and animal welfare must be observed. Permits must be obtained for both catching the animals and for sending them on. Usually the project has to be approved as an "animal experiment" by the district or regional council.
technology
With direct bearing, a maximum bearing is usually carried out with the help of a yagi or parabolic antenna. Another variant is the Doppler direction finding, which, however, involves a higher technical effort and is only used for direction finding from stationary receiving systems.
Conventional wildlife telemetry has three components:
- the HF transmitter, adjacent to the animal
- the recipient, possibly with a data logger
- the antenna system with connecting cables
Channel
The miniaturization of transmitters has continued to advance in the last few decades. In the meantime, 2m transmitters with a weight of 0.6 g (e.g. PIP2 single button celled tag from BIOTRACK Ltd.) are commercially available. The transmitter weight should be below the threshold of 10% of the animal's body weight. The service life of the batteries depends on the transmission power of the transmitter and the space and weight capacities available. An essential factor for the signal strength is the quality and radiation possibilities of the antenna. Outputs of up to 1 watt ERP depending on the size of the animals are common. The VHF transmitters are mostly frequency-modeled and emit a "beep". In some cases, functions such as a “tree switch” are still used in the semi-professional sector. The beep speed changes when the position of the transmitter changes ( motion sensor ), for example when a dog stands on its hind legs. In the case of watertight housings, some of the transmitters are operated with a magnetic switch. The transmitters are therefore in operation for between ten days and one year, depending on the task at hand.
Antennas
Small dipole antennas , usually mobile and handy Yagi systems or HB9CV antennas , are usually used for location finding .
receiver
Special test receivers or semi-professional receivers from the amateur radio sector are usually used as receivers .
Frequency ranges
There are no officially assigned frequency ranges for wildlife telemetry. The transmitters are part of the location radio service and mostly work in the 2 m range (148–174 MHz). In the USA, the frequency ranges 40–50 MHz, 148–155 MHz, 160–165 MHz, 216–222 MHz are also used. The legal situation differs from country to country.
In Germany, a permit must always be obtained from the Federal Network Agency , which then issues a radio test license for radio-marking animals.
A number of small companies offer transmitter collars for dog owners. For these users in Germany, the transmitters have a transmission power of 10 mW and work on the SRD frequency 433.434 MHz. The use of this frequency is free of charge and registration in Germany.
Manufacturer
In the early years, scientists and the technical departments of the institutes produced the transmitters themselves. There are now a number of companies specializing in bio-telemetry, such as Titley Scientific , BIOTRACK Ltd. (Dorset, UK), Marshall Radio Telemetry (North Salt Lake, USA), Merlin Systems , ATS Inc. ( Isanti , USA), e-obs GmbH (Grünwald, Germany). Some of the companies are quite small and produce their devices with special modifications at the customer's request. In the meantime, companies also offer transmitters for “open frequencies” that anyone in Germany can use. They are used by dog handlers, falconers, etc. for hobby purposes. The technology used mostly comes from the field of amateur radio direction finding .
Publications
Books
- Joshua Millspaugh, John M. Marzluff (Eds.): Radio Tracking and Animal Populations . Ign Outdoor Activities (Plein Air), 2001, ISBN 978-0-12-497781-5
Ecological research using the telemetry method
- Frank-Uwe F. Michler, Berit A. Köhnemann, Goldenbaum; Mechthild Roth, Stephanie Speck, Jörns Fickel, Gudrun Wibbelt: Causes of death of radio-tagged raccoons (Procyon lotor L., 1758) in the Müritz National Park (Mecklenburg-Western Pomerania)
- R. Schulte, H. Wölfel: Final report on the research project . Satellite telemetry on red deer in the Harz Mountains . 1999.
- W. Stöhr (1988): Long-term heartrate telemetry in small mammals: A comprehensive approach as a prerequisite for valid results . In: Physiology & Behavior , Volume 43, Issue 5, 1988
methodology
- Devin S. Johnson, Joshua M. London, Mary-Anne Lea, John W. Durban: Continuous-Time Correlated Random Walk Model for Animal Telemetry Data . In: Ecology 89, 2008, pp. 1208-1215, DOI: 10.1890 / 07-1032.1
- F. Huettmann, Julia Linke: An Automated Method for Determining Wildlife Habitat Preferences in GIS and Telemetry Studies: A Flexible Software Tool and Examples of Its Application . In: Zeitschrift für Jagdwissenschaft , Volume 49, Number 3, pp. 219–232, DOI: 10.1007 / BF02189740
Web links
- GPS lynx telemetry in the Bavarian Forest National Park - The role of the lynx in the mountain forest ecosystem
- Monitoring of the lynx in the Bavarian Forest National Park BR contribution