McCann's skink (Oligosoma mccanni).
Very common throughout the South Island, does not occur in the North. Has a great variety of patterns.
Displaying an interesting threat response by holding it's tail in the air.
Striped and speckled morphs occur in the South Island, with the pattern possibly being associated with the dominant vegetation (stripes in grassland, speckles in scrubland).
From New Zealand Herpetofauna
"common skink" displaying threat response is actually McCann's skink