Geologically, it consists of Tertiary rocks, capped with loess and gravels, and surrounded by eroding cliffs and wave-cut reefs.

Other birds recorded as breeding there include white-faced storm petrels, sooty shearwaters, fairy prions, variable oystercatchers and white-fronted terns.

[2][3] The island has the only colony of white-faced storm petrels found along the coast between Cook Strait and the Otago Peninsula.

[2] Fur seals use rock platforms around the island as haul-out sites.

[3] The main vegetation type on the island plateau is introduced grassland.