New Zealand bird pollination studies – timeline
See how scientists have changed their ideas about the importance of bird pollination in New Zealand in the timeline below.
1870 – Decline of birds
There is a sharp decline in several native birds shortly after the accidental introduction of ship rats (Rattus rattus), coming on top of declines caused by years of forest clearance by human settlers. Some bird species become extinct.
Rats eating eggs
Rats are adapted to climbing trees and can locate nests easily due to their strong sense of smell.
1881 – Bird pollination not important
George Thomson publishes the first paper to state that bird pollination is not important in New Zealand. Early ecologists in New Zealand are influenced by ideas from Europe, where there are few bird-pollinated plants.
1885 – New pests
Weasels and stoats are first introduced to New Zealand to control introduced rabbits. They also eat young birds, so native bird numbers decline further.
Weasel with dead sparrow
A weasel (mustela nivalis) with it's prey, a house sparrow (passer domesticus).
1979 – Birds do visit flowers
Eric Godley publishes a list of eight bird species that visit 30 species of native plants. However, he thinks that, in most cases, birds are not important pollinators, as insects could do just as well.
Tūī on flax flowers
As a tūī searches flax flowers for nectar, pollen gets rubbed off on the top of its beak. At the same time, it leaves pollen on the stigma, completing pollination.
1989 – Birds disperse seeds
Mick Clout and Rod Hay state that birds are important for seed dispersal but bird pollination is rare in New Zealand. They realise some native plants are bird pollinated, but predict that future study will show the reduction in bird numbers is not a threat for pollination.
1992 – Explosive flowers
Jenny Ladley finds that flowers of Peraxilla (native mistletoes) only open and get pollinated when tweaked open by certain native birds.
1995 – Mistletoe problems
Jenny Ladley and Dave Kelly publish their concerns about mistletoes, which are bird pollinated. Low bird numbers means reduced pollination, so mistletoes are in trouble.
Mistletoe research
Dave Kelly the of University of Canterbury explains why native mistletoes are declining. He also talks about the research that he and Jenny Ladley carry out in Craigieburn Forest Park in the South Island. This includes using observations and measurements to provide a long-term picture and experiments to study pollination.
2000 – Rhabdothamnus pollination
Sandra Anderson discovers that bird pollination of Rhabdothamnus, a native New Zealand shrub, is failing.
2003 – Insects can’t replace birds
Sandra Anderson finds that – contrary to previous beliefs – if birds are not around to pollinate certain native flowers, insects do not appear to do their job instead.
2005 – Pollination by native bees
Alastair Robertson finds that small native bees can pollinate Peraxilla (mistletoe) flowers but not nearly as effectively as birds.
2006 – Exotic birds not helpful
Dave Kelly and colleagues test whether exotic birds can replace missing native birds. They show that exotics do very few visits, and 89% of visits to native flowers are done by bellbirds, silvereyes and tūī.
Male bellbird feeding
Birds such as the tūī, bellbird and silvereye are attracted to the brightly coloured flowers of the fuchsia tree. They receive nectar from the plant and pollinate the tree at the same time.
2010 – Reduced pollination a problem
Dave Kelly, Jenny Ladley and colleagues assemble evidence to show that reduced bird numbers is more a problem for pollination than for seed dispersal. This turns around what was thought just 20 years ago. Now, 12 native bird species are known to visit 85 plants.
2011 – No birds, no plants
Sandra Anderson, Dave Kelly, Jenny Ladley and colleagues use the native plant Rhabdothamnus to show how bird extinction can affect a whole ecosystem by reducing pollination and eventually reducing plant density.
Rhabdothamnus research
The Rhabdothamnus plant relies on bellbirds and stitchbirds for pollination. Dave Kelly of the University of Canterbury explains that, where these birds are absent, the plants are not surviving well. Research on offshore island reserves, with conditions similar to those on the mainland before bird numbers declined, has confirmed the link between low bird numbers and problems with bird-pollinated plants.
