|European Starling (sturnus vulgaris)|
I am actually painting some soldiers at the moment, but progress is so slow that there’s nothing to see, as yet, so I thought I might push my luck one final time and try readers’ patience by sticking with this Nature theme of the last couple of posts (a very broad heading, since Apple Crumble was in there, somehow).
You may well have seen this YouTube clip – I am fascinated by it. Two girls went out in a canoe on the River Shannon, and they saw some starlings.
In fact they saw rather a lot of starlings, and the starlings were doing something which these days is called a murmuration, though as far as I know "murmuration" is really just a collective noun for a bunch of starlings, without any stipulation of activity. These events are spectacular – I’ve seen films of similar behaviour by a cloud of budgerigars in Australia, I’ve witnessed this kind of formation flying by starlings, and I think I’ve heard of knots and fieldfares doing the same thing. Anyway, I’m impressed. I wouldn’t like to be standing underneath them at the time, but there are some well-known locations where starlings do this sort of thing regularly – Brighton is one, I believe, also Rome, and we have a famous site fairly near here at a shopping mall car park at Gretna, in the Borders, which maybe lacks the romance of Rome, but it’s the best we can do, and you can buy a very nice sweater while you are there.
Maybe the requirement is simply a very large number of birds all doing the same thing? Looking at the shapes, it looks like a travelling probability distribution; I realise that this is a dumb thing to say, but my starting point is that the location of each individual bird within the envelope shape must be subject to some kind of probability function. I understandthat some steps have been taken to come up with mathematical models to simulate this behaviour, but success is limited to date. Of course, since I don’t have the tools or the knowledge to stand a chance of getting anywhere, I have become very interested in understanding more of what is going on! [If I succeed, I shall next attempt to fly to the sun with wings made from a Corn Flakes packet.]
(1) We see pleasing shapes caused by the forces of Nature all over the place – they are very common – clouds of water droplets in the sky, sand dunes, waves on the sea, snowflakes – you will think of better examples than these. The difference with starlings is that they are intelligent – each individual is trying to do something, not simply being blown about.
(2) Birds don’t seem to do this if they are going somewhere – when migrating, for example, they do form recognisable shapes (skeins), but not like this. Maybe, since the murmurations seem to occur at predictable times of day (at least they do at Gretna), and in particular seasons, the birds are feeding, sweeping a limited area.
(3) Though the cloud of birds looks chaotic from the outside, each bird must have a simpler view – they must be aware of their immediate neighbours, who are travelling in the same direction; apart from this they must be guided by – what? – the light?
(4) Scientists have observed that within the cloud the birds space themselves so that they are grouped not too close to their neighbours (so as not to restrict flight and manoeuvre) but not too far apart (to avoid loss of contact and the “collective” feel). This “just right” spacing is known as the “Goldilocks” distance, and it has been observed that lateral spacing is tighter than are the gaps to the birds in front and behind (which makes sense for safe manoeuvre – this sounds more like the traffic on the M25 all the time - well, maybe not the M25, but on a more sensible road).
(5) If a bird becomes aware of its neighbours turning, it can react very quickly, but the accumulated delay across a large cloud would be expected to cause the effect of elasticity and the waves which we see on the films.
(6) Early attempts at modelling the murmurations on a computer looked at what happens if the birds instinctively fly towards the centre of the cloud (the darkest area) or directly away from it (towards the brightest light); although the centre is moving, and may be moving in a different direction from any individual bird at any particular moment, it is not a surprise to learn that the models showed that in the second case the cloud would simply disintegrate as the birds at the edges flew away, and in the first case they would tend to collapse into a single point, though the Goldilocks effect would limit how far this could progress.
(7) Perhaps, then, the birds are steering towards some intermediate condition of light (and therefore cloud density) which gives optimal feeding?
You will note that I have not progressed very far with this! I do not intend to sign up for a night-school course, neither do I wish to melt my brain (more likely), but I am gently interested in how this works. Nature is wonderful – we don’t really need to understand it, neither should we necessarily expect to be able to understand it, I think – but these bird clouds look like mathematical shapes to me, and I’d be pleased to get a better handle on what’s going on - I have never been a starling, but mathematics is what I was once trained to do.