Tuesday, 24 March 2015

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, recognized 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 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

Wednesday, 11 March 2015

Sawfly larvae

The Old Weetangera Road - horse-drawn carts and coaches used to drive along here. 

Autumn is well and truly here now in Canberra, making great mornings to be out in the bush, and on the weekend I went for a walk along the old Weetangera Road through the Aranda Bushland Nature Reserve. The birds are now in their winter flocks, with roving packs of Pied currawongs ranging through the canopy searching for insects, and the various passerines were in mixed-species flocks, rolling and weaving through the shrubs and lower branches.

A ball of Sawfly larvae hang onto the stem of a eucalyptus sapling - follow the arrow

How the birds spot and catch insects so quickly is always fascinating to watch, but one insect that few birds can tackle are sawfly larvae. I noticed a ball of these lying up for the day on a sapling gum tree. These are a species of Perga sawfly larvae, they spend all day huddled together for protection, then a leader of the pack leads them to forage out on the eucalypt leaves at night. Like all sawflies, these are hymenoptera and related to bees, wasps and ants.

A knot of Sawfly larvae lie up for the day
- they seem to lie head to tail, probably for cautious defence -protected at both ends

Another defense strategy they use is to release a nasty fluid from their mouths, based on eucalypt oils. Although they are called spitfires for doing this, they don't actually spit the fluid, it just sort of oozes out. The tactic is effective though and few animals bother them. Except, for example cockatoos, the local Gang-gang Cockatoos will pick one at a time out of the bunch, chew them, lick out the juicy contents and spit out the spiny skins.

They use their pointed tails to tap on branches,
a simple means of communication to keep the group together when feeding

To read more on these amazing insects click here to access the Victoria Museum website.

Saturday, 28 February 2015

Possum Raids Figs

The Brush-tailed Possum caught raiding the fig tree

After the success of catching the cockatoo raiding the chickens' food bins last week, I thought I should try to find out who was raiding the figs and focus a camera-trap on the fig tree.

The figs are the last fruit to ripen in our Canberra garden at the end of summer and we always look forward to opening a nice ripe one for breakfast. But, not this year, some animal has been eating them before we can pick them.

At first I thought it might have been fruit bats as I have seen them on the tree in previous years. Not this time though, the thief was a Brush-tailed Possum. It was a female, probably the one that sleeps in one of our garden nest-boxes, although if it was her, she has parted with her joey. The last time I saw her a week or so ago, she had a large joey (a young marsupial) in tow, still trying to hitch a ride on her back even when it was at least half mum's size.

She will probably have a new tiny joey in her pouch already, so I suppose she will want to add a hint of fig flavour to her milk. Lucky possums.

To watch a clip of the surveillance film, as evidence of the criminal's identity, click here.

We do like the possums, but...... there are times......

Monday, 23 February 2015

Scribbly Gums

A rich mix of old and young trees in Black Mountain forest
I have noticed that there have been many more features on wildlife than wildpaces lately in the blog, so I shall try to adjust this. First off, this gave a reason to go for a walk in one of the local forests, the 500 ha Black Mountain Nature Reserve, which is only two kilometres from Canberra city centre  The woodland is dominated by two eucalyptus tree species, Scribbly Gum Eucalyptus rossi and Red Stringybark E. macrorhyncha, and the under story is mostly a sparse covering of grasses and short shrubs. The trees provide thousands of cavities for such animals as possums and parrots - especially Crimson Rosellas, while I often see swamp wallabies and echidnas working through the undergrowth.

Wild forest in the foreground - urban high-rise only a mile away
There are numerous tracks to follow through the forest and multiple variations of routes to take. On today's walk I went around the summit and looked down onto the city. And I noticed how, even the city looked green with the street and park trees shining between the buildings.

A zoomed-in view of Canberra city from Black Mountain
Now that it is late summer, some species of eucalypt trees have shed their outer layers of old bark to reveal shiny new skin. The Scribbly Gums do this but not the stringybarks.

This fine old Scribbly Gum has large and small hollows,
 it is a true veteran, yet is still throwing up young branches from its old trunk.
The cast bark lies thick on the ground in some places, giving homes and shelter to all sorts of animals, but it can build up deep enough to become a fire hazard and Canberra, as the bush capital, is well aware of the danger of bush fires. So there are regular burn-offs of the ground cover over the years to prevent such a risk.

Shards of bark lie about the base of the gum trees, their inner surface glowing red in the sunshine
The Scribbly Gum is named after the marks on its bark, which are especially noticeable when the bark is freshly cast. These scribbles are the marks of where a species of moth larvae, Scribbly Gum Moth Ogmograptis scribula, have meandered safely beneath the old bark layer, while munching on the fresh growth immediately below. To find out more on the moth and its larva, click here to a link to the Australian museum website.

The zig-zag trail left by a scribbly gum moth larva - its journey began at the thin end of the trail, where the adult moth had laid her egg. The trail ends at the thick end where the larva emerged and crawled into a crevice to form a cocoon. The  adults emerge in the autumn.

Thursday, 12 February 2015

Crafty Cockatoo

A mug shot of the robber cockatoo
A few days ago I noticed that someone had seemed to have left the lids off the bins used to store the chicken food - we have chickens roaming free-range in our back yard. Then I saw the lids off again and thought there must be something else to the tale. So, I set up a camera-trap for security surveillance.

It wasn't long before the culprit was caught red-billed. It was a Sulphur-crested Cockatoo Cacatua galerita who was raiding the bins. These are regular, daily, visitors to the garden and they often roost with us up in a high gum tree. They are well-known to be clever birds, so I was not greatly surprised to see who the villain was, but I was surprised at how quickly it adapted to overcome my defences.

Watching from atop the chicken shed

The cocky found it too easy to flip off the lids themselves, even the clip-on lid of the larger bin, so I placed bricks on top of the lids. But, still too easy. The bird simply stepped onto an adjacent bin or tree stump to gain a firm base then used its strong bill to lever open the lids, casting the bricks aside with the lever action. To watch a two minute video of the crafty cocky click here.

The bird opened the large bin first, but as that only contained chicken pellets, it wasn't too happy. It had obviously been watching me feed the chickens and wild birds, noting that I was taking seeds, especially sunflower seeds out of the bins, but which one? It didn't take long to open them all and dive into the bottom of the white bins for the sunflower seeds.

It looked like there was only one bird that had learned how to open the bins as others came and tried, but with no luck. The trick was in stepping back and using the leverage. The clever bird reaped the reward first, facing off contenders before eventually allowing more to join in the feast as it became more satisfied.

There were seven or eight in the flock at one stage, until I heard the commotion and stomped down to the far end of the garden to chase them off.

And the solution - two bricks on each bin, with the bins far enough apart to deny any leverage.

Caught in the act