Bird responses to kānuka and poplar silvopasture on a hill country sheep and beef station in Aotearoa New Zealand : a thesis presented in partial fulfilment of the requirements for the degree of Master of Environmental Management at Massey University, Manawatū, New Zealand
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Date
2024
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Massey University
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Abstract
Historically, agriculture in Aotearoa New Zealand has been associated with mass deforestation and subsequent erosion. A popular way to counter erosion in hill country sheep and beef agricultural systems has been to plant exotic poplar or willow silvopastoral systems, however recent studies have explored the use of low density kānuka plantings as a potential native alternative. This study explored how both current poplar/willow and proposed kānuka plantings affect the movements of birds in a hill country sheep and beef station. It analysed the density of trees in various poplar/willow and kānuka groves via the use of a GIS dataset of individual trees across the Wairarapa region. Tree densities were used to generate four sampling categories (Open Pasture, Poplar/Willow, Low Density Kānuka, and High Density Kānuka), and 5-minute bird counts were undertaken in each of these categories. Results show that native and endemic bird counts grew significantly as kānuka density increased but counts of native and endemic birds in Poplar/Willow sites were often lower than those in Open Pasture. Introduced birds showed a similar increase in counts in Poplar/Willow as in Low Density Kānuka. Overall, the native species the benefitted the most from the presence of kānuka were the small insectivorous passerines: grey warbler (Gerygone igata), silvereye (Zosterops lateralis), and fantail (Rhiphidura fuliginosa). No native birds favoured Poplar/Willow sites, however native birds were sometimes witnessed moving through the canopy when poplar plantings bordered kānuka groves. Introduced European starlings (Sturnus vulgaris), chaffinches (Fringilla coelebs) and yellowhammer (Emberiza citrinella) all benefitted from the presence of both poplar/willow plantings and kānuka groves. Significant numbers of introduced Eurasian skylark (Alauda arvensis) and endemic New Zealand pipit (Anthus novaeseelandiae) were present on Open Pasture sites. Given the positive response of on-farm native bird populations to the presence of kānuka, its use as a silvopastoral plant has great potential to align conservation goals with the economic realities of agriculture. There is long term potential to form bird corridors out of silvopastoral erosion mitigation, however more work still needs to be done to fully understand the complexities of on-farm birdlife.