Harmonic Radar - a Method Using Inexpensive Tags to Study Invertebrate Movement on Land

New Zealand Journal of Ecology (1997) 21(2): 187-193 ©New Zealand Ecological Society conductor with nonlinear characteristics, a diode, is illuminated by radar waves, it can re-radiate an harmonic of the original radar signal. This harmonic signal can be detected and used to locate the reflector together with anything attached to it. The energy to operate the reflector is delivered by the illuminating radar. The harmonic radar is such a device. It is a hand-held emitter which generates a continuous, unmodulated wave. Diodes are available that reflect the signal at double the original wavelength. The harmonic radar unit also detects the reflected signal and transforms it into an audible signal. The harmonic radar was originally developed to locate avalanche victims and it was first used for tracking invertebrate movements around 1985 (Mascanzoni and Wallin, 1986; Hockmann et al., 1989; Wallin, 1991). The reflected signal is not specific, so individual markings have to be applied to the animals if they are to be identified once they are found. In this communication we call attention to the potential usefulness of this equipment for tracking invertebrates in New Zealand. We present detection distance data for several types of diodes which can be used as transponders, and provide examples of its use for tracking the short term movements of a ground beetle and long term movements of an endangered snail.