Scientists have long been interested in recording data from freely moving animals. For larger animals, several telemetric techniques are available not only for following the movement of unrestrained animals in the wild (White and Garrott, 1990) but also for transmitting measures of heartbeat, body temperature, wingbeat, respiration, etc. (e.g. Lord et al. 1962; Butler and Woakes, 1980; Funk et al. 1993; for an overview, see Amlaner and Macdonald, 1980). Because of the size of such transmission devices, however, data acquisition has been restricted to larger animals. The development of lightweight batteries and microchips has only recently facilitated efforts to transmit data from smaller animals such as insects. Such data should greatly enhance our understanding of the processes involved in the neuronal control of unrestricted behaviour. Eventually it should be possible to monitor the activity of individual units (neurones, muscles) under closed-loop conditions, which closely resemble free movement. It is to be expected that this new approach will surpass previous studies involving intact but surface-bound animals implanted with long flexible electrodes (for crickets, see Kutsch, 1969) or animals tethered in a windstream (for improvement of the flight balance device, compare Weis-Fogh, 1956, with Dombrowsky, 1991). Increased freedom has been achieved in experiments on ‘free flight’ of large insects (Mohl, 1988; Stolley, 1990), although even these animals were restricted to a short or stationary flight handicapped by several implanted flexible electrodes.

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