Tuesday, 31 March 2015

Exotic Sparrows

A female House Sparrow takes a bath
I have been a bit busy recently and haven't had time to keep up with the blog, but I did take time to appreciate the humble House Sparrow on the 20th March - World Sparrow Day. The House Sparrow Passer domesticus is one of the most cosmopolitan birds and here in Australia it is an exotic bird - introduced from a foreign country, i.e. the UK about 150 years ago. Some people don't like them as they are an introduced species and as such they have no legal protection, but I like them and admire them.

A Crimson Rosella in the garden
Exotic is an overused and often miss-used word, which when applied to birds usually refers to brightly-coloured species from foreign places, such as parrots. Well, some the the commonest birds in our Canberra garden are parrots; especially Crimson Rosellas, Eastern Rosellas and Sulphur-crested Cockatoos. I have seen more than ten species of parrot in or over the garden, but none is exotic. The sparrow is exotic.

A flock of House Sparrows digging for seeds in the garden
It's autumn now and the sparrows are moulting into their duller winter plumage, the flock has built up to its high point - and soon there will be Collared Sparrowhawks coming in and taking a few (there is a big clue in the name). Last Spring the flock went down to only two or three birds from a peak of about twenty. But House Sparrows are survivors.

They really can dig
However, if sparrows are survivors, why are they are in decline in the UK? If we are losing sparrows, then there must be something changing in the environment. These birds are never far from human habitation, being mostly an urban species and only venturing into rural areas if there are farms or other settlements. They don't 'invade' other habitats. They can be an agricultural, or bio-security pest by eating grains or fruits, or entering piggeries. Although, perhaps they could be regarded as a biological early-warning device. Why are they declining in the UK, too many human-made chemicals in the environment? Remember, these birds only live in close proximity to humans, so if their environment if being damaged, so is ours.

But they keep themselves clean
Meanwhile, as I write I can hear them chirping and splashing as they take a bath in the birds' water dish.
A happy, healthy sound.

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, 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

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.