RFID devices have been used extensively in animal tracking. They can be attached to moving animals and insects to track their movements and habits; since the devices can be made extremely small, they can be used even with very small animals and insects.
Both the tracking and the miniaturization ability of the RFID was demonstrated in a study by University of Bristol researchers recently. In the study, the scientists implemented very small, less than 3mm RFIDs to the backs of rock ants in order to study their nest choosing habits. They created a host of ants nests with the well built nests about twenty times farther away than the poorly built nests, and then started a crowd of rock ants on a journey towards the nests, with a tracking device attached to their backs.
The RFID devices were useful in identifying the number of ants, their movements to the nest, their selection, and also how many ants moved from the nearby poorly built nest to the faraway but well built one. The tiny nature of the device did not impede any movement on the part of the ant. Moreover, the ability of the RFID to automatically transfer and accumulate signal came in handy here, because without that, it would have been impossible to manage hundreds of minute ants. Just imagine stamping a bar code on the ants and trying to get them to walk under a hand held laser device in order to track them!
RFID devices have other implementations in the animal world. They can be used to track large animals in reserve forests, especially when it is not a good idea to go near the animal. They can also be used to track the movement of migratory birds, much like the tracking of aircraft by IFF transponders, a technology that is as old as the first World War.