Birds’ roles in ecosystems
An ecosystem consists of all of the organisms living within an area and the interactions between them and the physical environment.
All ecosystems, whether they are marine, freshwater or located in native bush, involve the transfer of energy. Energy flows into an ecosystem usually via sunlight. This light energy is used in a process called photosynthesis, allowing plant matter (flora) to grow. Flora then becomes a food source for birds, animals and insects. This transfer of energy continues as feeding relationships occur between plants and animals.
Tūī feeding
Tūī and other birds (bellbirds, kererū and weka) feed on fruit from native trees. These birds assist in the seed dispersal process, allowing seed germination to occur.
Mutualism
Native birds interacting with the flora in our ecosystems have a mutualistic relationship – that is, they both benefit from the relationship. While the bird receives nectar or fruit (in the form of berries) from the tree it visits, the tree benefits by having another organism carry out the process of pollination or seed dispersal. Many native trees cannot perform these processes without the intervention of birds.
Birds are the primary pollinators and seed dispersers in New Zealand native bush.
Pollination
Pollination is the process where pollen is transferred within and between plants enabling fertilisation and reproduction.
Bees, wasps, butterflies and (most importantly in New Zealand) birds act as pollinators. These organisms carry pollen grains from the anther to the receptive part (stigma) of the plant to allow pollination to occur.
Flax (Phormium tenax), kōwhai (Sophora microphylla), northern and southern rātā (Metrosideros robusta and Metrosideros umbellate) and tree fuchsia (Fuchsia excorticata) are New Zealand native trees all pollinated by birds. Our native birds are attracted to the flowers of these trees and carry pollen from flower to flower on their beaks as they seek nectar, pollinating flora as they move.
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.
In New Zealand, birds are important pollinators. The honeyeater family consisting of tūī (Prosthermadera novaeseelandiae), bellbirds (Anthornis melanura) and silvereyes (Zosterops lateralis) perform the majority of pollination by all birds in our native bush. Two native species of mistletoe (Peraxilla spp.) require the finely refined beaks of tūī or bellbirds to tweak open their flowers and allow pollination to occur.
Nature of science
Science is a process of trying to figure out how the world works by making careful observations and then making sense of these observations. Scientists have used this knowledge to inform their understanding of ecosystems and the interactions between species within these systems.
Seed dispersal
Over 70% of plants in our woody forest in New Zealand have fleshy fruit. Many seeds located within these fruits have coats that must be weakened by chemicals as they pass through the digestive system of another organism.
Native plants are dependent on birds for successful seed dispersal and regeneration. Once a seed has passed through the digestive tract of a bird, it will often be dropped far away from the host tree’s location, enabling the tree to potentially colonise a new area. As many of our native birds are now confined to small predator-proof mainland sites or offshore islands, what might the future hold for our native flora, which is so dependent on this process?
In New Zealand forests, only 12 species of bird have been responsible for the majority of tree seed dispersal, but many are now extinct:
Extinct – piopio (Turnagra capensis), 2 species of moa with small gizzard stones (Euryapteryx spp.), huia (Heteralocha acutirostris)
Confined to predator-proof mainland sites or offshore islands – saddleback (Philesturnus carunculatus), hihi (Notiomystis cincta), kōkako (Callaeas cinerea), whitehead (Mohoua albicilla)
Present on the mainland – tūī (Prosthermadera novaeseelandiae), bellbird (Anthornis melanura), kererū (Hemiphaga novaeseelandiae), weka (Gallirallus australis).
The importance of fruit size
Trees that produce the largest fruit (>14mm diameter) almost solely rely on the kererū for seed dispersal. These trees include miro (Prumnopitys ferruginea), pūriri (Vitex lucens), tawa (Beilschmiedia tawa) and taraire (Beilschmiedia tarairi). Within any species, there is variation, and on any given tree, there will be a variety of fruit sizes along with variation in the size and gape of a bird’s beak. This factor will allow the smaller tūī and bellbird to disperse some of the seeds from these trees.
Kererū feeding on kawakawa
The kererū has the widest gape out of all New Zealand native birds. This enables it to eat the largest berries in the forest. The kererū is important in the seed dispersal of large native berries in forest ecosystems and trees, such as the kawakawa, rely on native birds for seed dispersal.
As the weka is a flightless bird, it can only scavenge the fruit that has fallen from the tree and could not cover the same distance that a bird of flight would be able to. Therefore the 3 keystone species for seed dispersal in New Zealand are the kererū, tūī and bellbird.
New Zealand native birds have a key role in the pollination and seed dispersal of our native flora. Birds are essential to ensure the future of our native bush ecosystem in generations to come.
Activity idea
In the activity New Zealand bush ecosystems students build a food web that represents the New Zealand bush ecosystem.
Related content
Find about more about pollination and fertilisation.
The articles Flower parts and Te haenga me te ruinga o te kākano ❘ Pollination and seed dispersal have helpful background information about the plant parts and their purposes.
Find out about some of the research New Zealand scientists are doing to investigate the effect the decline of native birds has on flowers that rely on them for pollination.
Useful links
See the biodiversity section on the Ministry for the Environment website.
