Friday, 27 November 2015

Millions of butterflies

A Caper White Belenois java butterfly passes through the garden

For the past week there have been white butterflies passing through our garden in Canberra, lots and lots and lots of them. They are on migration moving across southern New South Wales, heading in a broadly easterly direction. The species is Caper White and during the peak number day - last Tuesday, the 17th - I counted an average of seven per minute pass through a hundred metre long corridor between our garden and those of our neighbours, which are aligned north-south. They were flying through all day, so I reckon that there were 420 passing through per hour, which would make a few thousand during one day. The main front seemed to go through that day, but there are still a few stragglers about, some of which might be stopping locally, others are still moving east.

Almost all the butterflies were males, I maybe saw two or three that looked like they might have been female,
but they never stopped so I could not be certain. Where are the females?

There were reports of them from a wide area around Canberra, so I wonder how many were in the flock? I saw similar numbers flying in the same easterly direction as I was walking and driving around the area, so the density was possibly at the same scale over a much wider area. If so, there would have been 4200 per hour crossing a one kilometre line. The plains area of the Australian Capital Territory is about 25 km wide from north-south which could have seen about 100,000 butterflies move  through (I don't know if they passed over the forests and ridges, but if so that would bring the ACT width to approximately 90 km and approximately 400,000 of them).

A stop to re-fuel

So, if they were flying for about 10 hours that day at the same density (which they seemed to do near me) there would have been approximately a million passing through the ACT in that one day. Even if these figures are wrong, there were numerous butterflies on passage for a few days, so overall there would likely have been more than a million altogether, possibly many more. And the butterflies were flying across a wider area, hundreds of kilometres wide across neighbouring parts of New South Wales, so how many million were there on migration. Where did they come from and where did they go. I know many were seen down at the coast about 200 km to the east, and many must have stopped there, but why were they moving from west to east. My friend and local butterfly recorder, Suzi Bond will, I hope, come up with the answers. She dropped me an email about half an hour after I first noticed the unusual number in the garden. She had seen them too.

How many flowers were pollinated by so many butterflies?

This sighting reminded me of a similar butterfly day I had a few years ago while driving from West Wyalong to Canberra. That was through farming country, mostly wheat and canola oil. There was what seemed to be a miriad of Cabbage White Pieris rapae butterflies along the road verges. So I counted, well estimated, how many there were per kilometre of road and for how far along the road. It was a three hour drive and there were clouds of them for most of the way. There were x between the road and the field fences per one kilometre strip and I traveled y kilometres with them at similar densities (I forget the exact detail of the count, but I do remember the total as it was so mind-boggling). I saw at least 2,000,000 Cabbage White butterflies in one day. And there were many, many more farther into the fields, there were flickers of white all over the landscape, dotting the canola crop especially. Those butterflies weren't migrating though, there just seemed to have been an enormous synchronised emergence.

Two true wildlife spectacles, played out by common garden insects. Wonderful.

A male with ragged wing edges - how far had he flown?

Friday, 20 November 2015

A living twig

A caterpillar - or a twig
lies on a mix of fallen bark, leaves and branches
While walking through the bush a few days ago, a few kilometers from the centre of Canberra, I found this caterpillar hiding amongst some cast bark at the base of a gum tree - a Scribbly Gum. The caterpillar's camouflage was superb, and it wasn't moving, which would have given it away. But my eye was scouring the leaf and bark litter for spiders, especially peacock spiders which are magnificent if not rather tiny and very tricky to spot. But more of them in a later blog, for now follow this link to read more on them: PeacockSpider

The caterpillar is the one on the right, no the left...
The caterpillar was perched on a fallen branch lying beside fallen bark and twists of twigs which it looked just like. I think it was the distinctive caterpillar shape of a long body, hunched up and ending with two pairs of feet at the rear that attracted my eye. Then once I focused on it, of course it was obvious, yeah that would be right.

I thought it would be a moth caterpillar, and probably of the Geometridae family, and it was. It is a Fallen Bark Looper moth caterpillar Gastrophora henricaria, and it is widespread across south-east Australia. The caterpillars eat gum leaves, up in the canopy during the night, then hide in the ground litter during the day, so that all fits with what I found.

Caterpillars have six true legs as in their adult morph - and they have ten prolegs. The true legs are positioned on the thorax, as in the adults, tight behind the head. The prolegs are spread down the rest of the body and in the Geometridae  three pairs have been atrophied, leaving just two pairs close to the rear. This gap in their leg layout causes them to walk with a looping action, hence the name looper.

A looping motion as it walks and two pairs of prolegs at the very rear - a looper caterpillar
There are quite a few gum trees in the forest I was in, it is several kilometers square, so I wonder how many Fallen Bark Looper moths and their caterpillars there were in the forest - thousands, many thousands - and I only saw one. So, yes they are very well camouflaged animals indeed.

Thursday, 5 November 2015

Nest re-cycling

The male Tawny Frogmouth Podargus strigoides sits on the edge of the chough nest

Tawny frogmouths usually build their own nest, a simple platform of twigs and sprigs of greenery, although about one in forty nest records from my study of these birds in Canberra have been in old White-winged Chough Corcorax melanorhamphos nests. These are large, clay nests, which resemble bronze-age beakers set half-way along horizontal branches. In this case about fifteen metres up a Scribbly Gum tree. Frogmouth nests are often flimsy constructions, so perhaps they find these old firm structures as good bases for their nest. They add a few sprigs inside the cup, but don't fill it.

The female sits with the chicks - she has more red on her wings than the male

I have been monitoring the incubation, brooding and feeding rates of frogmouths over the years, studying differences in habitat and weather conditions. Some of this can be done by watching, but it is at times easier and less time-consuming to do this remotely with wildlife-monitoring cameras. So, with the help of Laura Rayner, who did the climbing to this nest, we set this one up, which was about fifteen metres up a gum tree. Once the camera was set and tested, we left the birds for the night and collected the camera the next night. I only approach these birds at night as I do not like to disturb them during the day when they can be vulnerable to predation. They behave so confidently at night, and these birds were feeding their chicks as we were setting up the camera a few metres away.

The chicks, at about two and a half weeks old, were beginning to fill the egg-cup nest

In this case, the adults fed the chicks seventy times overnight, so that was perhaps thirty-five feeds per chick, if they received equal shares. I don't know as I can't identify each chick in all the shots. About half the feeds were in the first two hours after dark, then the feeding rate decreased as the night progressed. And each adult only brooded the chicks for one period of about ten minutes, most of the time the chicks were alone in the nest.

Then as dawn approached the male came in to cover the chicks for the whole of the next day, for it is the male who guards the chicks all day, while the female roosts in a nearby tree. To watch some footage from the camera click here.

A chick peers over the lip of the clay nest

Sunday, 1 November 2015

Tawny Frogmouth fledglings

The adult female Tawny Frogmouth Podargus strigoides (left) male (centre) and one fledgling adopt their cryptic pose
- to merge with the branches they are perched upon

The chicks of the earliest breeding tawny frogmouths which I study have just fledged. They left the nest on the night of the 29/30th October and had flown to a tree about 75m away for their first daytime roost. One chick was with the two adults but the other was on its own in a nearby tree.

The male sits over the chick to protect it - all three birds sit in a relaxed posture as there is no threat of danger, it was only me and they probably recognised me, through familiarity, as not a threat

It is usual for each adult to sit close by a chick if they are on separate branches or trees. This one was perhaps not being guarded because it was on a low branch and the adults were a bit cautious to sit so low. Although they were watching over it and would likely have swooped down to protect it if any predator did approach it. All they did when I approached, was lift and turn their heads to watch me intently, as if ready to move if necessary.

One fledgling had landed in an adjacent tree
 - and was not being guarded by an adult, which is unusual
The solitary chick had little to fear however, as it was so well camouflaged against the tree bark and as they do, it sat motionless as I walked past. Most people or predators would not have noticed it.

The fledglings' plumage was still very downy. The main feathers to have developed were their flight feathers on their wings, and the feathers on their backs which would be able to shed any rain and camouflage them against the tree bark. The facial bristle feathers were beginning to take form, hiding their eyes and bill, for now that they have left the nest concealment is essential to their survival as they roost during the day.

Wednesday, 14 October 2015

Possum twins

The female Common Brushtail Possum Trichosurus vulpecula which lives in our back garden,
 with a single youngster

October is the time for the local brushtail possums in Canberra to be carrying their large young around. We have two females in our garden, shared with our human neighbours, and they both have young. One has the usual single youngster, but the other has twins, which is uncommon. It seems that it is also rare for both young to survive. However, these twins seem to be growing well and it looks like they will both survive.

The neighbouring female in the front garden walking across the drive with her twins on her back

I often go out at night watching for wildlife, and it is noticeable how I have spent hours in the local woods and only seen a few possums in that time. Then when I walk back through the adjacent suburbia, I seem to see a possum in every other garden. This and the set of twins (I have seen possums with twins in the garden before) are signs that there is good feeding to be had for possums around humans. They are one species that is a successful urban survivor.

Doubled up on top

The youngsters have a yellow/orange tinge to their fur which gradually fades to the grey of the adults, as can be seen by the difference in colour between the larger and smaller twins.

The twins are growing fast and putting on weight
The twins can climb already as I have watched them follow their mum as they walked along the branches, but they still take the easy option and travel on their mother's back whenever they can, which is still most of the time. I think that will soon stop.

There is no easy way to climb down a tree with twins on your back
Especially if they make climbing difficult for their mother, for such encumbrance would in  the long run make the whole family vulnerable to predators. So the next stage of evolutionary behaviour will kick in soon and they will have to become more independent. Then we will have three more possums galloping across our roof at night. Mmmmmmm, a bit noisy.

Those prehensile tails can be a nuisance sometimes