Restoring tūī in Hamilton
Tūī feeding on kōwhai flowers, a preferred food, at Lake Waikari. Image - Neil Fitzgerald.
Tūī are found in most New Zealand forests and in many towns but are scarce where nearly all forest is gone, especially in the South Island east of the Southern Alps. They are also scarce in Hamilton in the central Waikato. Public reports and surveys by John Innes and his team prior to 2004 showed that tūī appear in rural and urban places in the Waikato from about May until October, and that they feed mainly on nectar of exotic Banksia integrifolia, camellias, flowering cherries and eucalypts, plus native kōwhai.
Neil Fitzgerald attached small radio transmitters to the tails of tūī captured in Hamilton to record their movements and habitat use (the transmitters fell off when the birds’ tail feathers moulted in the autumn). The average length of ‘vegetation patches’ that tūī foraged in was 62 m and these had a mean canopy height of 11 m. The vegetation was 91% planted, and was dominated (64%) by exotic species. Within each patch there were, on average, four individual trees that tūī fed on. Distances between the patch and the nearest house varied considerably, from 0–300 m. Tūī are obviously quite happy near houses and roads.
In spring, tūī flew 12–20 km back to native forest areas to nest (map). Nesting success of forest birds in New Zealand is typically poor – only around a quarter of all attempts succeed – due to predation by pest mammals, especially ship rats, possums and stoats. This is also true for tūī in the Waikato, since only 3 of the 11 tūī nests found in this study successfully fledged young.
To improve tūī nesting success, the Waikato Regional Council (WRC) offered to target two key pests – ship rats and possums – in the forests where radio-tracked tūī went to breed. In 2007 WRC launched Project Halo in which these pests were managed to very low levels with various regimes of best-practice toxin application, including 1080, anticoagulants and others. Pests were successfully targeted in a pulsed regime of 3 years of toxic baiting followed by 2 years of no baiting.
Biennial counts in August of bird species and numbers in urban Hamilton by John’s team (in partnership with the Hamilton City Council) since 2004 showed that the proportion of count stations with tūī in parks and other green areas of the city increased from around 6% to 23% between 2004 and 2010. This was undoubtedly due to WRC’s pest control.
In December 2007, for the first time in living memory, tūī nested in Hamilton at the Hamilton Gardens. One nest in a macrocarpa was unsuccessful but a nest in bamboo successfully fledged chicks. Observations in 2011–2012 of tūī chicks and fledglings in Hamilton, combined with the sustained summer presence of tūī in parts of the city that had none in previous years, suggest that the number of tūī nesting (rather than just visiting) has recently increased greatly. Better data on this will be obtained when counts resume in November 2012.
The future focus of this management and research will be on protecting tūī and other birds nesting in the City with predator control similar to that undertaken in surrounding forests. John and his team will also explore whether the locally rarer bellbirds (korimako) and kererū are also increasing.
This research is funded by the Waikato Regional Council, Hamilton City Council and the Ministry of Science and Innovation (Programme CO9X0503).
