Techniques for tracking amphibians: Harmonic radar versus radio telemetry, and the effects of tag attachment

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Abstract

To gain information on the microhabitat use, home range and movement of a species, it is often necessary to remotely track individuals in the field. Radio telemetry is commonly used to track amphibians, but can only be used on relatively large individuals. Harmonic direction finding can be used to track smaller animals, but its effectiveness has not been fully evaluated. Tag attachment can alter the behaviour of amphibians, suggesting that data obtained using either technique may be unreliable. We investigated the effects of external tag attachment on behaviour in the laboratory by observing 12 frogs for five nights before and five nights after tag attachment, allowing one night to recover from handling. Tag attachment did not affect distance moved or number of times moved, indicating that the effects of tag attachment are unlikely to persist after the first night following attachment. We then compared harmonic direction finding and radio-telemetry using data collected in the field. We fitted rainforest stream frogs of three species with tags of either type, located them diurnally and nocturnally for approximately two weeks, and compared movement parameters between techniques. In the field, we obtained fewer fixes on frogs using harmonic direction finding, but measures of movement and habitat use did not differ significantly between techniques. Because radio telemetry makes it possible to locate animals more consistently, it should be preferred for animals large enough to carry radio tags. If harmonic direction finding is necessary, it can produce reliable data, particularly for relatively sedentary species.

Keywords: amphibian; behaviour; ecology; techniques; radio tracking; harmonic radar; harmonic direction finding