Developing indices of relative abundance for monitoring cave and ground wētā (Orthoptera) in southern beech forest, New Zealand

ABSTRACT

We sampled populations of forest-floor dwelling cave and ground wētā using footprint tracking tunnels and spotlight transect counts in southern beech forest, New Zealand. Samples were compared to estimates of wētā density based on mark–recapture estimates from 25 m² enclosures. Both activity indices captured variability in cave wētā in time and space, were strongly correlated with each other, and have the potential for monitoring cave wētā activity levels. Comparisons between indices and cave wētā density estimates were equivocal, as recapture rates were too low to calculate high-resolution density estimates. We also found that cave wētā counts had a curved relationship increasing with temperature, and a negative relationship with increasing shrub and woody debris cover. Based on these preliminary results, tracking tunnels could be a viable method of monitoring cave wētā as they appear more efficient than transect counts and are relatively inexpensive. However, further calibration trials are needed to determine if indices mirror robust population density estimates.

KEYWORDS:

• Rhaphidophoridae
• Anostostomatidae
• indicators
• invertebrates
• invasive species
• nocturnal
• tracking tunnels

Acknowledgements

We are grateful to Shanna Rose, Jason van de Wetering, Maddie van de Wetering, Dan Palmer, Antje Leseberg, and Kerry Weston for assisting with field trials, Peter Johns for identifying wētā, and Eric Edwards, Stephen Hartley, Corinne Watts, Chris Green and Warren Chinn for providing valuable advice on the design of the trials. Corrine Watts and an anonymous reviewer provided helpful comments that improved this manuscript.

Associate Editor: Dr Rob Cruickshank.

Disclosure statement

No potential conflict of interest was reported by the authors.

Additional information

Funding

This study formed part of the Department of Conservation Science Investigation 4231, and was conducted with the support of a Victoria University of Wellington Summer Scholarship.