Movements of tūī in the Waikato
While reinvasion by pests is unhelpful during or after control programmes, one common objective of pest control is to get valued native species to reinvade places where they were formerly abundant. Translocation may be required if the nearest desired colonists are hundreds of kilometres away, or where inhospitable landscapes provide a barrier to colonisation. On the other hand, some species are intrinsically very mobile and readily colonise new sites by themselves, as managers of many sanctuaries are currently discovering.
Tūi is one such mobile species. When nesting, tūī home ranges are only a few hundred metres across. But in the spring and winter when nesting is finished they undertake much larger journeys, frequently travelling up to 20 km to access seasonally available nectar of species such as coastal Banksia, camellias, eucalypts and kōwhai.
For the last decade, Neil Fitzgerald, John Innes and team have studied tūī in Waikato in two different contexts. First, working with Waikato Regional Council and Hamilton City Council, they showed that pest control in forest fragments 8–15 km from Hamilton has increased the number of tūī visiting the city in winter about 15-fold since 2007. Tūī are also reasonably common nesters in the city so some are resident all year round (see Kararehe Kino 20, June 2012). Second, Neil and John have monitored tūī ‘spillover’ from Maungatautari, a pest-free (except for mice) sanctuary in the central Waikato, and it is this work that is described here.
Maungatautari is a 3400-ha reserve of tawa-dominated forest, protected by 47 km of pest- fence, and has been largely pest-free since late 2006. Landcare Research monitoring at Maungatautari shows that mean tūī counts doubled from 2 to 4 per count station between 2002 and 2011. Neil and John also investigated whether tūī have increased outside the sanctuary. The landscape around Maungatautari was divided into four 5-km bands (Fig. 2) and the residents were asked two questions: What was the most tūī you saw at your property at one time last winter? Do you think that tūī at your property have decreased, stayed the same or increased in the last 2 years?
Questionnaires were delivered to about 2000 properties in late 2006, with the number of questionnaires scaled to the area of each zone. The survey was repeated biennially (2008, 2010, and 2012) with identical questions put to the 307 initial respondents and 218, 199 and 161 responses respectively received.
Results showed that tūī increased greatly outside the sanctuary as well as inside it (Fig. 1), with average maxima increasing between 2006 and 2012 from 6.3 to 16.6 in the 0–5 km band, from 4.9 to 23.6 in the 5–10 km band, from 3.6 to 6.9 in the 10–15 km band and from 3.9 to 6.9 in the 15–20 km band.
Most residents’ subjective opinions about tūī increases agreed with these data. Over all zones and years, 55% of respondents thought that tūī had increased since the previous survey; 31% thought they had stayed the same; 9% thought they had decreased and 5% were unsure.
The team’s results show that Maungatautari is one of several managed sites in the Waikato that are improving nesting success of tūī, and that there is a spillover band at least 10 km wide around the sanctuary in which this species has greatly increased. There is much to learn about how widely other species will range from the many kinds of sanctuary now being developed on the New Zealand mainland and its nearshore islands, and which native species will disperse to production and urban landscapes.
This research is funded by the Ministry of Business, Innovation and Employment under Contract CO9X0503.
John Innes & Neil Fitzgerald
Fig. 1 Average of ‘most tūī seen at one time’ by residents in 5-km bands around pest-fenced Maungatautari Reserve, central Waikato, from 2006 to 2012, arranged by year (top) and distance (bottom).
Fig. 2 Five-kilometre bands around the pest-fenced Maungatautari Reserve in which residents were surveyed about tūī ‘spilling over’ from the sanctuary. The edge of Hamilton City is just visible at top left.
