Spring Flora

False Sarsaparilla Hardenbergia violacea 

It has been a wet Spring in Canberra this year, following a wet winter, so there is lots of growth sprouting in the bush. All the plants need now is a bit of sunshine and warmth to bring out the flowers. Although the fruit has blossomed well, I fear that there have been too few insects out and about to pollinate them. I'll know in a week or so, and the local wild flowers might be having the same problem.

Alpine Grevillea Grevillea australis

Nature is full of surprises though and when I was out for a walk through the forest on Black Mountain the other day I was amazed at how many flowers were out in bloom. Purple tufts of False Sarsaparilla were creeping over the ground and up through shrubs, the local native grevillea, the Alpine Grevillea, was showing as well as such a shy flower can show, and the moist air was rich with the scent of wattle - several species were in flower. While all around there were tiny single-flowered orchid stems. Their subtle tones hidden, then shown, by shadows and speckles of light dropping through the leafy canopy.

Box-leaf Wattle Acacia boxifolia

The main insects I saw were Painted Lady and Cabbage White butterflies. Although of course to our human eyes, those would have been the obvious ones. I did see some flies dotting about and several caterpillars on leaves. A few were stretching and folding themselves across the paths after a rain shower. I hope there were more.

Dusky Fingers Caladenia fuscata - white form - about 10 cm tall
(Highly sensitive, very rare/threatened)

Yet, once again, despite all the abundant purples, reds and yellows, filling the woodland with a coloured haze, it was the teeny inconspicuous orchids that stole the show. Why are we attracted to orchids so much? Well, for me, it is the way such small, highly specialised plants can grow in such nutrient-poor soils. They were literally shooting straight out from the leaf and bark litter on the forest floor, with nothing but a poor stony soil beneath.

Dusky Fingers Caladenia fuscata - pink form

These finger orchids are so short that we have to get down on our hands and knees, or lower to see the detail of their flower forms. Yet, they are probably holding their flowers at a perfect height to catch the attention of passing flies or whatever insect they rely on for pollination. For, as witnessed, most flies that I did see were hovering and wandering through the forest at just such a height as they passed through the low shrub layer. There was probably another set of insects flying through the canopy, where the next layer of greenery grew.

Blue Fingers Cyanicula caerulea 
(Highly sensitive, very rare/threatened)

It's good to take a ground level look at the world now and then. To see it as others do.

Bird Pollination

An adult male Eastern Spinebill sitting on a grevillea bush outside my study window

I've been at the desk a bit too much recently, but it is has turned out quite entertaining as our garden in Canberra is busy with birds - and they have been a great distraction. Right outside the window, about a metre from me as I type, there is a small flock of Eastern Spinebills Acanthorhynchus tenuirostris feeding on a flowering grevillea. Spinebills are a species of honeyeater, and like their name suggests, they specialize in feeding on nectar, which grevilleas produce in abundance.

An adult spinebill dips its bill into a grevillea flower for nectar

An immature spinebill dips its bill into the same grevillea flower.
These birds are about sparrow size.

Grevilleas are part of the protea family and they have a highly adapted form of flower. The inflorescences - the flower spikes - have multiple flower heads held in tight clusters and with over three hundred species, they come in lots of shapes and sizes. They have evolved to be pollinated by different species of birds, insects or small marsupials, such as sugar gliders, but especially honeyeaters. There are over 60 species of honeyeater, mostly in Australia and the two families have similar geographic spreads in the general Australia/Oceania area. So, the honeyeaters are probably the main pollinators.

A Spinebill hovers to feed from a pendulous inflorescence.
Honeyeaters have evolved to feed on nectar like hummingbirds, but they are not so well adapted for hovering flight. However, they can also creep through the branches and feed safely under cover away from predators, and  humming birds can't do that, or do they need to?

Grevillea flowers have an exaggeratedly long style which unfolds with a sticky pad of pollen grains around the stigma at the tip, the pollen-presenter. The pollen is transferred from the anthers to the style as the flower opens and there are some unfolded styles in the first two photographs above, they are the curling loops above the petals. The nectar sac is cunningly concealed between fused petals and can only be reached via a slim opening. An opening which the spinebills can probe into with their fine long, curved bills, but many other animals can't gain access - this pollination strategy is selective towards species that can transfer the pollen. As the birds dip their bill into the nectar, they touch the pollen-presenters and a deposit of sticky pollen is left on their crown. Then, when the birds fly to another grevillea plant, they brush against another flower's pollen-presenter and the pollen is passed onto the style and into the stigma. And that's it, all done, the flower has been pollinated.

A Spinebill is dabbed on the head by a pollen-presenter as it feeds from a flower.
This bird is a juvenile, recognised by the fold of yellow skin at the base of its bill, the gape, which is a leftover feature of a fledgling. It will soon lose this, and the base of its bill will darken too as it grows into adult plumage during its first year of life.

Pollen sticks to the crown of this spinebill's head as it dips between a crowd of pollen-presenters

Spinebills, like other honeyeaters which are specialized nectar-feeders, have brush-tipped tongues, an adaptation that allows the birds to lap up the nectar from the tight space inside the nectar sac.They don't gain much per flower-visit, so these birds are busy when feeding, and they are busiest in the morning and late afternoon. Which is fine by me as I see them first thing and then at the end of a long desk session, without too much distraction during the middle of the day.

The tip of this spinebill's tongue can be seen as the white part protruding from the end of the bill - it's very delicate