An animal data gathering device comprise: a radio transmitter and receiver, a processor for controlling the operation of the device, and memory for storing, information including a first unique identifier associated with the device, wherein the processor is arranged to transmit a signal, by means of the radio transmitter, and to receive, by means of the radio receiver, one or more signals, each representing a second unique identifier from other devices and the processor is arranged to store in the memory each second unique identifier. Thus a record is kept of all radio devices with which the device has come into radio contact.