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 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 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.
Wonderful post John!
ReplyDeleteHow appropriate a posting when I first heard and then saw a pair this morning on a walk! Their nests ARE beautiful. I do like that image of the chicks demanding to be fed!
ReplyDeleteTop blog John. Very informative indeed. Great photos.
ReplyDeleteA welcome return to blogging with a wonderful article John. Great captures of the birds.
ReplyDeletePW