Radio frequency identification (RFID) uses a signal transmitted between an electronic device, such as a "tag", "transponder" or "microchip" and a reading device, such as a "scanner", "reader" or "transceiver". RFID technology identifies objects remotely through the use of radio frequencies.
The RFID or EID devices most widely used in animals are passive. Passive integrated transponders have no battery so the microchip remains inactive until read with a scanner. The scanner sends a low frequency signal to the microchip within the tag providing the power needed to send its unique code back to the scanner and positively identify the animal. Passive tags are designed to last the life of the animal providing a reliable, long term identification method.
The distance from which a tag can be read is called read range. Many factors contribute to the read range of passive tags including operation frequency, antenna power, tag orientation and interference from other devices. Low frequency tags are detected in milliseconds at close range from a few inches to about a foot (0.33 meter) in distance. Tags can be read through materials such as soil, wood and water. Ferrous metals and noisy environments can cause interference between the electromagnetic communication of the reader and tag.
PIT tags are typically injected subcutaneously using a 12-gauge hypodermic needle and syringe; they can also be externally attached using adhesives. Implant location varies depending on the species being studied, animal size and in some cases the behavior of the animal. Tags that are pre-loaded into an implanter, gas sterilized and individually packaged are available and convenient for tagging in the field.
The use of passive tags for animal identification and research provides many benefits including the reduction of error in recording data, rapid data collection and long term reliability. The value of PIT tags has been successfully demonstrated in studies of mark and recapture, survival, movement, behavior and distribution for a variety of species.