Is Maungatautari restoring bird pollination and seed dispersal services?
Degree GrantorUniversity of Canterbury
Degree NameMaster of Science
The decline in range and density of many native New Zealand birds from mammalian predation has raised concerns over the functioning of ecosystem processes such as pollination and seed dispersal. At Maungatautari, almost all mammalian pests have been eradicated from within a pest-proof fence enclosing 3400 ha of native forest. I examined whether Maungatautari is restoring pollination and seed dispersal services to native plants, compared to a nearby non-treatment site, Pirongia Mountain.
Five-minute bird counts made at Maungatautari and Pirongia (in 2002 and 2005 prior to pest eradication from Maungatautari, and in 2008 and 2010 following eradication) indicated that 10 of the 12 individual bird species examined showed significant changes in abundance following pest control. Six species showed an increase in abundance, including bellbirds (Anthornis melanura), tui (Prosthemadera novaeseelandiae) and kereru (Hemiphaga novaeseelandiae). Counts of all native species combined increased at Maungatautari while counts of all exotic species showed no trend over count years.
In December 2010, 140 five-minute bird counts showed tui and bellbirds, key pollinators, to be more abundant at Maungatautari than Pirongia. Higher pollen loads on the stigmas of both female and hermaphrodite Fuchsia excorticata flowers at Maungatautari, compared to Pirongia, suggest that F. excorticata at Maungatautari received better pollination service. Fuchsia excorticata pollen loads collected from 67 sites around New Zealand indicate that female plants at sites with lower abundances of mammalian predators generally received better pollination service. Hermaphrodite F. excorticata plants had similar and high pollen scores in all regions, except for in the North Island.
Five-minute bird counts in December 2010 also showed that kereru and blackbirds (Turdus merula), key seed dispersers along with tui and bellbirds, were more abundant at Maungatautari than Pirongia. A second measure of bird abundance, maximum counts, showed flock sizes of tui, bellbirds and kereru were larger at Maungatautari, but only significantly so for tui and bellbirds. Fuchsia excorticata fruits were removed more rapidly from plants at Maungatautari than at Pirongia (a 6-fold difference). There was twice the density of tawa fruits (bird cleaned and fleshy) under trees at Maungatautari compared to Pirongia, perhaps from reduced mammalian fruit predation. There was no significant site effect on tawa dispersal service (percent of fruit consumed by birds), but a significant site x fruit density interaction, suggests birds at Maungatautari provided better dispersal service to large fruit crops. A similar number of miro fruit (bird cleaned and fleshy) were caught in seed traps under miro trees, but a greater percentage of fruits were consumed by birds at Maungatautari (59%) compared to Pirongia (26%).
The results from this thesis indicate that increased densities of key native birds at Maungatautari are providing better pollination and dispersal services to the native plants examined. Projects which increase the density of key bird mutualists, such as tui, bellbirds and kereru, on the mainland, may have positive benefits for pollination and seed dispersal mutualisms.