Harmonic direction finding: A novel tool to monitor the dispersal of small-sized anurans

摘要

The suitability of harmonic direction finding for tracking of dispersing juvenile natterjack calamita) and green toads (B. viridis) was evaluated in laboratory and field experiments. a first step, dipole reflector tags were developed which combined low mass, small size and detection range. The average mass was 114 mg, wire antenna length 42 mm and detection usually varied between 2.5 in and 12.5 m - occasionally reaching 26 m - as assessed using commercial portable scanning device RECCO 5000. In toads that had a snout-vent length of mm, the mass of the reflector tag did not exceed 10% of the toad's body mass. Tags were attached by glueing to the dried dorsal skin of the toadlet. In a replicated laboratory almost all tags were shed 36 hr to 48hr after attachment. In 2001, 417 juveniles toads equipped with reflector tags and their dispersal was studied in a natural habitat (Urmitz, Germany). The recovery rate of reflector tags was similar in B. calamita n=33) and in B. viridis (31.6%, n=103). The maximum distances between release and site were 588 m in B. calamita and 665 in in B. viridis. Results obtained suggest that new method is better suited for monitoring the migratory activity and habitat use of small anurans than passive tagging systems presently in use, such as microtags and passive transponders (PIT). Nevertheless, detection range is still too small to rival active systems such as radiotransmitters which remain unsuitable for small anurans.