There cannot be ravens here

Part 9 of the Spooky black birds of SoHo series, for my #AnimalMOOC Field Note – expedition to urban West Hobart

There cannot be ravens here.

I say this because of this tree:

IMG_5284It is a persimmon, larger than, but not dissimilar to the one growing next door in my neighbours yard, which the local corvids were observed to strip.  It is un-netted, and covered in a glorious array of sunburst coloured fruit.

I’ve never seen a raven in the centre of town, except perhaps flying overhead.  Town central is more the domain of weedy birds, like the introduced sparrows, starlings, and blackbirds.

Ravens like hanging around  human landscapes, eating the treats we have thoughtfully provided for them, but apparently, not in the middle of our small city.  Is this a function of the distance to the nearest forest perhaps?  Or do the potential costs of negative interactions with humans potentially outweigh the benefits of this extra food bounty.

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The spooky black birds of SoHo (Part 4) – too cold for corvids?

#AnimalMOOC Field Notes, Part 4: The chilly edition – in which the birds hide from me, and I am too cold and sooky to chase them down.

Yesterday morning when I woke up, the mountain was dusted with snow.

snowy mountain

Mount Wellington, or kunanyi in a local indigenous language, looms over large over the town and peoples of Hobart, physically and sometimes metaphorically. In Hobart, the Mountain is the centre of all things –  defining topographical feature, super-sized weather vane, and reminder that our small city is tied directly to the Tasmanian Wilderness World Heritage Area, by geology and by vegetation.  And when there is snow on the Mountain, Hobart is cold.

Forest ravens and currawongs abound in Tasmania’s mountain regions.  The currawongs in particular are drawn to areas inhabited by unwary backpackers, and will wait, patiently, beady-eyed,  for the moment when a sandwich is left unwatched, a pack left unattended.  I’ve had a bushwalking friend tell of a currawong encounter at a track junction on the well-travelled Overland Track. Other bushwalkers had foolishly left their hiking packs, zips exposed, trailside, as they bagged a nearby peak.  My friend had arrived to a currawong-facilitated shambles of torn food packaging, strewn socks and ravaged apples, just before the pack owners returned, who promptly accused him of this wanton vandalism.  He protested his innocence, pointing out that if he’d been rifling through their packs, he would have taken more than their muesli bars.  He told them about the currawongs, but they refused to believe him.

If they’d done even a little research, they’d have discovered that currawongs in high-traffic bushwalking areas are renowned for their cunning ways with pack zips – they grab onto the zip tabs with their strong beaks and yank open bags, to get at the tasty trail mix within.  They are very naughty birds!

In my street, they show similar guile in dealing with netted fruit trees.

In yesterday’s chill, there seemed to be fewer ravens around in the forest across the road – although I  could hear them about, I struggled to set eyes on them.  Then I remembered my neighbours’ persimmon tree.  I wandered next door to find that the birds had completely stripped the netted tree – they’d simply unpicked a bit of the netting and pushed their way in, scoffing all of the fruit, to my neighbours’ mild annoyance.  But none were to be found in their yard today, probably because they’d eaten everything that was of any interest.

I suspect the colder weather has changed their distribution, which would be interesting to look into.

Black currawongs are known to be altitudinally nomadic, moving down hill in winter, and returning to the mountains as spring returns.  They turned up here a few months back in numbers I hadn’t seen, possibly moving to take advantage of better food sources in the lower, warmer, urban areas.

Like many non-traditionally-aesthetically-pleasing, common animals, the Forest Raven is relatively little studied, and many basic details of its behaviour and ecology are not necessarily known.  It’s thought that mated pairs hold permanent territories of around 40 hectares, but this is likely to vary with availability of food resources.  Non-breeding birds hang out in flocks of about 30-40 birds, with groups swelling to mobs of up to 100 over Tasmanian winter.

Later in the afternoon, I walked up the mountain a little, looking for them in the roadside forest tracts, but once again, could hear, but not see them.  I suspect that the birds who are normally in the forest across the road from my house have probably moved en masse to the tip, and are propped up on the nice warm compost piles picking at the dinosaur bones.  But it’s far too chilly for me to go and test this hypothesis 😉

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All of the details of bird ecology in this post are taken from Pizzey and Knight, 2010. The Field Guide to the Birds of Australia (8th edition). HarperCollinsPublishers Australia Pty Limited.

The spooky black birds of SoHo (Part 3) – I go to the municipal tip!

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See that tiny little dot on the blue sky? That, my friends, is a Tasmanian Forest Raven!

#AnimalMOOC Field Notes, Part 3: The glamour edition – In which I go birding at the municipal tip, and buy a nice new tea cup.

Went for a walk down the fire trail today, across a couple of valleys to the local tip, to see what the ravens were doing.

Although it was a relatively sunny day, this is Tasmanian winter, and as I traipsed down into the cold-air drainage zone adjacent to the rivulet, I cursed my lack of clothing.  In my precarious, propped-up-by-cold’n’flu-tablets state, it really wouldn’t do to tip over the edge into seriously debilitating lurgy.

One of my fieldwork rules is, where possible, never to go out in weather that is distracting. If its raining hard enough to dissolve your ‘waterproof’ paper, hot enough to melt your sunglasses, or windy enough to knock trees over, chances are, you won’t be paying adequate attention to the survey you’re supposed to be undertaking.  Today was really not so bad.

As I dropped down diagonally down the ridge towards the rivulet, the numbers of ravens seemed to thin out.  When I looked up, I usually saw one or two of them flying in the general direction of the tip.

The tip is quite close to my house, as the corvid flies, but about 2km on foot, according to the inter webs.  It’s really not far for the ravens near my house to go for a bit of fetid food hunting, as can be seen in the map I have bodged up below –

The blue line is for those without wings...

At the tip, I had a chat to Colin, one of the Resource Tip Shop Co-op’s workers, who works with the rest of the team there to salvage and sell things that other people would otherwise condemn to landfill.

“What are the binoculars for?” he asks.

“Um, there’s this assignment I’m doing for an animal behaviour course I’m studying…so I’m looking at ravens.  Wonder if any of my ravens from up the hill are here?”

“Yeah, good luck working that out – there’s hundreds of them!”

Of course, if I trapped and tagged them, I could work out if any of ‘my’ corvids were dining on the tip face, but this is a little outside the scope of my current investigation.

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Shiny new tip shop! Has been recently upgraded. Although you can’t see them, there are plenty of ravens flitting about the forest edges.

Colin goes on to regale me with stories of raven mischief at the tip.  He sees them and the local seagulls as rival gangs, fighting turf wars for the best bits of garbage – the ravens will form a sort of flying wedge, landing amidst a mob of seagulls, taking that new turf as their own.

“They keep very separate,” says Colin, “and the seagulls never go into the forest.”

“That’s because they’re seagulls!” I say, feeling cleverer than I actually am, “They are no forest gulls, but there are forest ravens!”

“Mmmm,” says Colin.

We discuss their migration habits a bit, and ponder as to where they sleep.  The gulls make a daily commute from the coast to the tip for the day, before returning to the coast to roost.  The ravens, we’re not so sure about.

“They probably sleep in the forests at the edge of the tip,” says Colin.

I note this down in my mental field notes book, and go to have a quick squizz at the “animal books” section of the shop.  Anything to do with animal behaviour is for some reason interspersed with publications focussing on the British Royal Family.

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Serried rows of delightfully decomposing organic matter, Hobart Municipal Tip. 9 in 10 SoHo corvids rate this as the #1 restaurant in this suburb.

 

I buy a fetching eggshell green tea cup, and head up to the industrial composting facility to check out the corvid action.  Here, a few dozen ravens are busily picking over the tops of the steaming compost heaps, looking for tasty morsels.  They flap away like broken umbrellas as I try to take their photos.  Although this is primarily a green waste facility, other organic matter is also composted, which might provide reasonable pickings for the birds.  I spot a few skulls, probably once belonging to sheep, and a huge bone which I suspect of being dinosaurian in origin.

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Dinosaur bones! Dinosaurs that looked a lot like our modern sheep…

I’m also surprised to see a rather attractive little male flame robin (Petroica phoenicea), posing prettily on an emergent twig next to a steaming vent in the compost.  If you look very carefully in this blurry, backlit photo, you can just see him – I think he only hung around because I was wearing a red jacket – robins do seem to be rather competitive.

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I call this piece “Flame robin on compost heap”. I’m sure Australian Geographic will be after the rights to this pic any moment now.

I wonder how many of the ravens rely on this as their primary food source. Do they defend their patches against other ravens? Or do they move through freely, picking up a bite to eat wherever they fancy? And perhaps most importantly, what proportion of their diet is made up of stolen sandwiches from inattentive council workers?

I file these thoughts in my mental notebook for further examination once my head cold clears a little, and clutching my shiny new tea cup, head for home.