12 Memorandum : Vibration effects on amphibians (Leiopelmatid frogs) 64524 Vibration effects_memorandum (15 June 2022)_Final Rev 0 Archey’s frogs maintained their brooding posture, even when the frogs were “prodded”, for up to 17 days after they were collected off egg clusters that were soon to hatch. These observations suggest a strong innate behavioural predisposition to brood even when male frogs are disturbed. Auckland Zoo did, however, also record egg abandonment on several occasions, as well as the detection of unfertilised eggs. Several possible explanations for these recruitment failures have been considered, one of which includes the potential effects of anthropogenic vibrations inside the specially designed shipping container used to house the Archey’s frogs at Auckland Zoo. Reportedly, a broken floor support and movement in the floor panels while keepers moved around inside the facility created frequent increased vibrational disturbance that may have contributed to the egg clutch abandonment rates seen (R. Gibson pers. comm, January 2022). Although this hypothesis is largely speculative and no measurements were made of the extent of increased vibration (if any) the frogs actually experienced, anthropogenic vibration effects on captive animals have been reported in the literature. Garner et al. (2018) reported behavioural responses in laboratory rodents to vibration caused by routine husbandry procedures and Felt et al. (2012) demonstrated morbidity and mortality in aquatic African clawed toads in a laboratory setting in response to adjacent construction vibration. As such, potential vibration effects on Archey’s frogs at Auckland Zoo cannot be completely dismissed but it is more likely that other influences such as unnaturally high stocking densities (i.e., multiple frogs per m2) may have been a larger contributing factor to lowed breeding success in the captive frogs (R. Gibson pers. comm, March 2022). While there is little information on male Archey’s frog behaviour and movements while brooding eggs, it is likely that some movement occurs because egg-brooding frogs have been known to defecate, indicating they had eaten despite brood-care (Bell, 1985). If frogs temporarily move away from eggs to feed and then return, it seems plausible that if a male frog were to respond to an extraneous disturbance stimulus (e.g., vibration) by moving off an egg-cluster, it may return to brooding shortly after the stimulus ceases given their high investment in caring for eggs and ensuring successful recruitment. Disturbance effects (e.g., startle response or movement away) during the dorsal brooding phase might be less consequential because males are more mobile and simply carry the froglets with him on his back. 8.1 Conclusion The role of anthropogenic substrate vibrations in disrupting animal behaviour is poorly understood and the field is largely under researched. Theoretically, Leiopelmatid frogs do have the anatomical apparatus to detect vibration and the unusual aspects of Archey’s frog ecology (e.g., egg-brooding) suggest that extraneous vibration stimuli might influence behaviours. However, no evidence has been found to verify vibration sensation or perception in leiopelmatid frogs, let alone the positive or negative responses of these frogs to natural or anthropogenic generated vibrations. In Archey’s frog, the high level of investment in egg care by males does suggest that this species can tolerate some level of disturbance and the persistence of both Archey’s and Hochstetter’s frog populations in the immediate vicinity of the mining operations at Golden Cross suggests both species can tolerate some levels of vibration despite differences in biology and ecology. Indeed, the Golden Cross vibration modelling indicates that vibrations of 2–10 mm/s for Hochstetter’s frog and 2 mm/s (maybe up to 4 mm/s) for Archey’s frog are likely to be tolerated. It is important to recognise though, that the Golden Cross data does not provide evidence of a vibration threshold above which a response that is meaningful in an ecological sense could be expected.
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