New Zealand Journal of Ecology (2007) 31(2): 169- 185

Sampling skinks and geckos in artificial cover objects in a dry mixed grassland-shrubland with mammalian predator control

Research Article
Deborah J. Wilson 1*
Robin L. Mulvey 1,2
Ryan D. Clark 3
  1. Landcare Research, Private Bag 1930, Dunedin 9054, New Zealand
  2. Present address: Department of Botany and Plant Pathology, Cordley Hall 2082, Oregon State University, Corvallis, Oregon 97331-2902
  3. Department of Zoology, University of Otago, PO Box 56, Dunedin 9054, New Zealand
*  Corresponding author

Introduced mammalian predators threaten populations of endemic New Zealand lizards but their effects on lizard populations have not been quantified on the mainland. We trialled the use of artificial cover objects (ACOs) for sampling small terrestrial lizards (the skinks Oligosoma maccanni, O. nigriplantare polychroma and O. inconspicuum, and gecko Hoplodactylus maculatus) in three experimental mammal-management treatments: a mammal-proof fence, two sites in an intensive mammal-removal area, and an experimental control site with no mammal removal. These predator control regimes were established in 2005-2006 to protect endangered grand skinks (O. grande) and Otago skinks (O. otagense) at Macraes Flat, North Otago. We (1) counted skinks and geckos found under ACOs on a single day and compared these counts between treatments, and (2) estimated lizard population sizes (N) based on capture-mark-recapture (CMR) of lizards under ACOs in daily and weekly sampling sessions. Our results provide baseline data of the abundance of the small lizard species shortly after implementation of predator management. Single-day counts of skinks were significantly higher inside the mammal fence compared with the experimental control. No consistent differences were found between the other treatments. Significantly more skinks were counted in gully habitats than in ridge habitats. Nˆ, counts of skinks from the first day of CMR, and the total number of individuals caught were correlated, but these relationships must be validated with independent data. Few geckos were caught unless ACOs were placed near rock outcrops. Only two skinks but 25% of geckos moved between adjacent ACOs (5-m spacing). The recapture rate of skinks was low; captures declined when ACOs were checked daily but not when they were checked weekly. Because of potential biases of these methods, we propose to compare counts in ACOs and Nˆ based on CMR in ACOs with Nˆ based on CMR in pitfall traps with 3-m spacing.