Mistletoe and Mistletoebirds – a fascinating relationship

The text for this post was prepared for an article in BirdLife East Gippsland’s newsletter, The Chat, Number 62 December 2014.  Some of the photos and captions have changed.

Mistletoe is a name applied to parasitic plants that grow on other plants and derive water and nutrients from their host. Mistletoe is widespread throughout the world including Australia where there are numerous species adapted to growing on many species of host plants. Willis et al in their Field Guide to the Flowering Plants of Victoria state there are 12 species of mistletoe in Victoria with Drooping Mistletoe (Amyema pendula) (Loranthaceae) probably the most common species. Jean Galbraith in her field guide, Wild Flowers of South-East Australia, lists some 21 species for a larger area. There will be many more species for Australia.

Mistletoe are seen by some as pest plants as heavy infestations may kill the host tree, usually when it is weakened by disease or drought. However mistletoes are important plants as they add greatly to biodiversity, providing significant quantities of high quality food. Also their dense foliage provides excellent roosting and nesting opportunities. 240 bird species have been recorded nesting in mistletoe, some 75% of Australia’s resident bird species.

The Mistletoebird, a species of flowerpecker, is native to Australia, where it is widespread, and some of the islands to our immediate north, though it is absent from Tasmania. As the name implies, the Mistletoebird has a close association with mistletoe plants and in Australia is probably the main species responsible for the spread and on going survival of mistletoe. While Mistletoebirds do eat the nectar and fruits of other plant species, and also insects and spiders, their diet is heavily concentrated on the fruits of mistletoe and their digestive system is specifically adapted to this specialised diet.

The mistletoe fruits can pass through the Mistletoebird’s digestive system and be expelled within 4 to 25 minutes. The fruits are ejected with little change and the sticky surface allows the seed to stick to the bark of plants where it has a chance of taking hold. The Mistletoebird actually wipes the seeds onto the branches of plants as they are excreted, thus promoting the spread of their principle food source.  

Male Mistletoebird - they are brightly coloured but hard to see and most often detected by their call.

The more sombre coloured female Mistletoebird.

The specialised diet of mistletoe berries and the adaption of the Mistletoebird’s digestive system to this diet starts very soon after the young birds hatch. Apparently the young birds are first fed on insects, however mistletoe berries soon become a prominent part of the young bird’s diet.

The following sequence of photos, starting with the beautiful nest, show the young being fed mistletoe berries and the associated waste management process.

Mistletoebird nest in Snowy Daisy-bush.

The female Mistletoebird builds the nest with no help from the male. She lays between three and four eggs and incubates the eggs herself. After the eggs hatch both parents feed the young.

The Morecombe field guide nest section (p416) describes the nest as follows, “The suspended nest is tiny, neat, soft and pear shaped, made of plant down densely bound with webs to create soft, felt-like walls. The shape and the soft thin walls, like fine woollen knitting, have led many to describe the nest as being like a baby’s bootee”.

The walls may be thin however they are tough and withstand the rigors of both the young birds as they rapidly grow within the nest and the many visits by the parents, who cling to the nest to supply food and take away waste.

The nest must stand up to the rigors of parents making possibly thousands of visits to the nest and up to four rapidly growing and active young.

This nest was constructed in a Snowy Daisy-bush (Olearia lirata) near the top about 1.6 metres above the ground surface where it was moderately exposed not only to photographers but also to potential predators.

At this nest, only the female came to feed the young.  In this case there were two young, a smaller clutch than the usual three or four? The male was too shy to come near the nest while I was nearby taking photos. It is possible however that the male was supplying the female with food and she was bringing it in to the young while I was there.

Each time the female came in she followed more or less the same path landing on a stem of the Daisy-bush about half a metre from the nest before landing on the nest itself. The young were often aware of her approach well before I was, as they started calling with wide-open mouths thrust out from the nest entrance before she appeared, no doubt they were alerted to her approach by a single call.

The female approaching the nest with mistletoe fruit. She followed the same path on most visits.

She always paused to check all was safe before making the last short flight to the nest.

The young birds in the photos are about a week old and the diet is mostly mistletoe fruits. They were being fed mistletoe fruits before their eyes opened. One fruit was delivered at a time. About every third visit waste fruits were taken away, usually three were expelled at a time by one of the young.

Both chicks were always very keen to be fed. How does the parent know which one to feed? It must be even harder to determine when there are four young.

The fruits were inserted well down the young bird's throats.

The careful removal of waste from the nest is practiced by many bird species, especially smaller birds. Apart from reasons of hygiene and the shear practicality of avoiding large volumes of waste accumulation in small nests, the removal of waste reduces the chance of attracting predators to the nest.

The chicks backed their rear ends well out of the nest entrance before excreting several partially digested mistletoe fruits which the female deftly collected.

Job done, female about to depart with another load of waste, which I assume she dropped somewhere away from the nest on her way to collect more fruits.

A fascinating and closely dependent relationship has evolved between a group of parasitic flowering plants and a single bird species.

When out in the field keep and eye open for mistletoe and wherever you find the plant Mistletoebirds will not be far away. They are fast and active birds not easily seen so learning their calls is a good way to find them. 

Mistletoe also attracts many other bird species, particularly honeyeaters, and nests of many species can often be found in the dense foliage.