Population numbers, response to weather, movements and management of the threatened New Zealand skinks Oligosoma grande and O. otagense in tussock grassland

Abstract

The threatened skinks Oligosoma grande and O. otagense currently exist in small, fragmented populations inhabiting rock outcrops among subalpine tussock grassland in southern New Zealand. This habitat is disappearing as farm production increases. Population numbers in three prime sites on Emerald Creek are low in absolute terms (11?56 individuals of each species; 15?78/ha). Low numbers and habitat fragmentation place populations at demographic and genetic risk. Emergence of both species from outcrops is highly weather-dependent, being negatively correlated with cloud cover and positively correlated with vapour pressure deficit and either air or rock temperature. Although higher numbers of both species emerge in warm, dry and sunny weather, O. grande is more likely than O. otagense to be seen in marginal conditions. Many animals showed site fidelity but some moved between outcrops; maximum distances between sightings were 139 m for O. grande and 79 m for O. otagense. Pair bonding may occur in O. otagense. We recommend that annual censuses with moderate-low confidence intervals be carried out at a range of sites, that future surveys and censuses consider weather variables explicitly, and that the effects of habitat degradation and habitat enhancement on dispersal between outcrops be investigated.