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.
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.
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.
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.
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.
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.
