Te Papa vertebrate curator Dr Colin Miskelly recently led a team that visited Takapourewa / Stephens Island Nature Reserve, to select and gather up 100 fairy prion chicks to move to Mana Island near Wellington. This is the fourth in a series of blogs about the project and the wildlife of Takapourewa.
Takapourewa holds a treasure-trove of rare and interesting wildlife, but this is only a fraction of what it could have been like, but for a fateful quirk of timing and geography. The 154 ha island lies off the northern tip of D’Urville Island, making it the outermost island of the Marlborough Sounds, and the first chunk of rock that seafarers encounter as they approach Cook Strait from the west. This meant that it was ideally suited for construction of a lighthouse when these proliferated around the New Zealand coastline in the late nineteenth Century. Unfortunately the technology of the time required lighthouses to be manually lit and watched over throughout the hours of darkness. This meant that the island needed people and houses, and a farm to feed them. And people like companion animals – in this case cats.
The combination of forest clearance and the introduction of cats on Takapourewa during 1892-94 led to the rapid extinction of several bird species (including the only surviving population of Lyall’s wren, and the last viable population of South Island piopio). Cats were eradicated by 1925, but the forest clearance continued to diminish the island’s biodiversity as salt-laden winds lashed the remaining patches of scrub-forest, causing further die-back and drying of the forest interior.
One of New Zealand’s largest ground beetles (Mecodema punctellum) was last collected on the island in 1931 and is likely to be extinct. Fortunately many other impressive insects survived, probably because rodents were never introduced. We were able to see some of the more notable inhabitants during our 4-day visit (but not all – the dry conditions in mid-January meant that some species stayed hidden).
The largest insect on Takapourewa is the Cook Strait giant weta (Deinacrida rugosa). This gentle giant survived naturally on Takapourewa, the Trio Islands and Mana Island, and has been introduced or reintroduced from these islands to many other sites (including Maud Island, Matiu/Somes Island, Titi Island, Wakaterepapanui Island, Zealandia, Long Island, Puangiangi Island, and Young Nicks Head). We found several giant weta while checking fairy prion burrows.
Wellington tree weta (Hemideina crassidens) on Takapourewa grow to a similar body-length as the giant weta, but are not quite as robust and heavy. They are mainly seen on tree trunks at night, very rarely descending to the forest floor, where they would be vulnerable to predation by the very dense tuatara population.
Several species of jumping weta are also present on Takapourewa, the largest of which is the striped, long-legged Gymnoplecton edwardsii. This species is common in the northern South Island and throughout much of the North Island.
Among the large flightless beetles that survived on Takapourewa are several species of nocturnal weevils. The flax weevil (Anagotus fairburni) is the same species that survived as relictual populations on several islands from the Poor Knights Islands south to a few outer islands in Fiordland. On Takapourewa, flax weevils cause only superficial damage to native flax (wharariki), in contrast to the population introduced to Mana Island, which has killed many hundreds of flax plants.
The ngaio weevil (Anagotus stephenensis) is a related, slightly larger species of weevil that feeds only on ngaio. Known to have survived only on Takapourewa, subfossil remains from South Canterbury indicate that it occurred on the New Zealand mainland before Pacific rats (kiore) were introduced. Ngaio weevils have recently been translocated from Takapourewa to nearby Te Kakaho Island.
One of the hazards to people visiting Takapourewa is the abundance of the giant tree nettle (ongaonga) along tracks and forest margins. This is the main host plant for admiral butterflies in New Zealand, and red admirals were common on the island during our stay.