Environment – Life cycle renewed

The abundant animal life on Tiritiri Matangi is supported by the soil and the plants that grow there. If you take the food pyramid familiar to biology students, a wide range and high biomass of invertebrates occupies the mid-part of the pyramid, above the plants, and they in turn are eaten by smaller numbers of birds and reptiles, which also eat the plants. Seabirds find their food at sea but nest on land. During their life, animal excreta fertilises the soil as do failed eggs and decomposing bodies. Some of the nutrients are washed into the coastal waters leading to more growth and variety of marine life.

This cycling of nutrients is exactly what we need on the island to ensure the plants and animals flourish. The difficulty we have is that many of the island’s animals and plants were lost during the farming period, as was much of the soil. 

To restore it, we have raised and planted thousands of trees and reintroduced reptiles, birds and one invertebrate, New Zeland’s largest wētā, the wētāpunga. But it takes many decades to re-establish the high levels of nutrient flows that previously would have occurred.

Thankfully, we didn’t need to wait until full nutrient flows were established to see the trees and other plants grow and for them to provide the vital food that supports all the other life. The life-support systems should continue to mature and improve but there is already plenty for visitors to see and enjoy.

Part of our work on the island is to monitor changes in the numbers and distribution of the wildlife and the wētāpunga are an interesting example. Releases were made at four locations on the island, and they have gradually spread as numbers increased. There are also nestbox projects to monitor the breeding success of the birds including for hihi/stitchbird, tīeke/saddleback, kākāriki/red-crowned parakeet and tītitipounamu/rifleman. We have over 150 tīeke nestboxes spread right across the wooded part of the island, but over the years the birds have increasingly turned to using natural sites for nesting and now only about a dozen are used each year. As part of the monitoring, we have been recording occasional wētāpunga in the boxes. A review of the data has provided an unexpected insight to their numbers and spread.

Over the past seven years the number of boxes occupied by wētāpunga have been 26, 47, 24, 51, 26, 72 and 113 and the number of individuals counted has risen from 27 in 2018-19 to 246 in 2024-25. Now we have a convenient means of monitoring our wētāpunga – but we’ll have to think of another way to follow the nesting success of the tīeke.