Today brings us to the end of Peregrine Week, celebrating one of evolution’s marvels. I’ve bought new binoculars just to see these birds—there are over a dozen pairs in Chicago, some right here on campus—and I’ll be watching the nests come spring. And if you’ve liked the excerpts from J. A. Baker’s The Peregrine, by all means buy the book.
Here’s a video of a peregrine repeatedly dive-bombing a flock of starlings. Notice how during the attack they stay together as a group; this is almost certainly for protection. A falcon can’t simply dive into a big flock of starlings, hoping to catch one—that would be suicide. It has to single out one bird and go for it. And that’s hard when all the birds are so thickly massed together. Note too how the birds seem to move as a unit.
The huge flocks of starlings that form in the evening, and are often seen in Britain, are called murmurations. They can number in the hundreds of thousands. The video below explains some theories about why these huge flocks form, but one of the biggest mysteries is how so many birds can move together so quickly, changing direction almost instantly. You’d think that if each bird followed its neighbor, a flock could change direction no more quickly than the sum of individual reaction times of the birds across the diameter. But it’s much quicker than that. Do the birds follow birds on the periphery of the flock rather than their neighbors? Who decides to change direction? This is an unsolved problem in animal behavior.
Below we see a huge murmuration of starlings in England, near Oxford. I’ve had the privilege of seeing this once in my life: near St. Andrews in Scotland. It’s an aurora borealis of birds!
The recovery of the peregrine falcon, once on the verge of extinction, is one of the great success stories of conservation. This video tells you a bit about it.
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[The hawk] returned an hour later, and perched in an apple tree at the edge of open ploughland. I sat and watched him from thirty yards, away from all cover. After two minutes of uneasy glaring, he flew straight at me as though intending to attack. He swept up into the wind before he reached me, and hovered twenty feet over my head, looking down. I felt as a mouse must feel, crouching unconcealed in shallow grass, cringing and hoping. The hawk’s keen-bladed face seemed horribly close. The glazed inhuman eyes—so foreign and remote—swivelled like brown globes in the long sockets of the moustachial bars. The badger-colored face was vivid and sharp against the sky. I could not look away from the crushing light of those eyes, from the impaling horn of that curved bill. Many birds are snared in the tightening loop of his gaze. They turn their heads towards him as they die. He returned to the tree, unsatisfied, and I left him alone for a while.
–J. A. Baker, The Peregrine
I enjoyed this so much – I bought the book! The UK edition with an intro by Rook expert Mark Cocker, has also excerpts from Baker’s diary & The Hill of Summer, Baker’s follow up (£20).
I recall mumurations of starlings used to be quite common in London but I have not seen one for years. The last time I did was when I was working at St.Paul’s Cathedral & had been cleaning graffiti off the Golden Gallery (at the top). I painted on a limewash & the architect had this great idea to paint on some fatty substance (I forget what it consisted of) to repell further graffiti attempts. A large flock of starlings settled up there. We speculated that they were attracted by the smell. (we used to get kestrals nesting in one of the towers as well, & once an escaped eagle owl roosted on a ledge). That reminded me that Darwin experimented with condors & smell – see the Friends of Darwin Blog I have just discovered –
http://blog.friendsofdarwin.com/2010/06/20100619/
Wow, I didn’t know that starlings formed flocks like that when they weren’t migrating. I’ve seen long lines of starlings (or some kind of blackbird) that took minutes to pass over head, but those were more or less traveling in one direction and didn’t have the amazing shape-changing properties of the murmuration in the video.
O. I wish it was a farewell to starlings – the bane of Uppsala. (Individually pretty, of course.)
Surely that can’t be true, depending on how you define “change direction” for a flock.
In physics it helps heuristics to do limit considerations. Then we can recognize the above situation as the maximum time, in the limit of an infinite flock that reverses direction.
The minimum time could be found by looking at liquids with the same near neighbor interactions. A river “changing direction” in a bend doesn’t have to wait for the outer flow line to get around the bend. In the limit of a hairpin turn the minimum time is the time for the individual flow element changing direction. For the birds the minimum time is then the individual reaction time.
The later is what you would expect of a leading edge swooping around. A similar limit behavior can be seen in the collective effect in liquids of surface tension and surface waves (which can travel much faster than volume waves). That happens basically because at the surface the molecules simply have no nearest neighbors in the directions away from the liquid.
My intuitive guess is hence what would help settle models would be to work out simulation similarities with movies of murmurations on some characteristic measures or flow patterns.
The rules governing movement in a flock/school/herd must be fairly simple. I would have said, turn left if your neighbour to the left turns left, turn right if your neighbour to the right turns right for example. Craig Reynolds used these criteria in modelling flocks in the 1980s -Separation: steer to avoid crowding local flockmates – Alignment: steer towards the average heading of local flockmates – Cohesion: steer to move toward the average position of local flockmates
See here – http://www.red3d.com/cwr/boids/
A quick search shows a lot of other ‘flock dynamics’ articles eg from the Journal of Theoretical Biology.
I don’t remembr where I saw it, but I have read something in the past year about the schooling behavior of certain types of fish, such as herring. The movements of these large dense schools of fish look very similar to that of the murmurations.
I don’t remember the details, except that I found it very interesting, but in the article I read the researchers hypothesis was that the individual fish were simply reacting to the movements of neighboring fish.
Other critters that move similarly in large dense groups are some insects, such as locust. A Dr. Clair Rind has done some interesting work on how locusts avoid collisions even when swarming. Check out this profile page on Dr. Rind. Near the bottom of the page are links to relevant publications.
Dr. Rind is even working with Volvo to design a collision avoidance system for cars based on her research. Here is a short video clip about that.
Another intersting aspect of the behaviour in the video is how the flock closes up into a dense ball as the falcon approaches.
The posts this week have been of particular interest to me as I have two local peregrines in London that I see almost every day, although mostly perched on tall buildings and not flying. Thanks.
Thank’s for this it’s been fascinating and thank’s for reminding me about J. A. Baker, I read both of his books in the early seventies but had almost forgotten about them. Took me back to some happy times when these and other similar books first encouraged me to go birdwatching.
I have greatly enjoyed your falcon postings and the excerpts from J.A. Baker’s “The Peregrine”. I will, with out doubt, be purchasing this book in the near future.
Thanks for this week of knowledge Mr. Coyne, thank you.
The starlings reminded me of fish schools that behave much the same way when attacked by a predator. And the predators also seem to have to pick out an individual fish. I guess I’m thinking of this video from the Planet Earth series. Sailfish vs. Sardines.
The spousal unit and I were discussing the UIC Peregrines this morning, and she said that it is considered a successful program as it has been in place for more than a decade now. There is a webcam for their nest also, but it is offline at the moment.
I ordered the Baker book yesterday. This has been a fun week here. Thanks, Jerry.
I saw this once when I was vacationing in Rome (in a November). Why is this a winter phenomenon? And is it restricted to Europe?
I think it’s a winter phenomenon because the birds are roosting together for warmth in some sheltered spot which is obviously going to draw predators, hence the defensive flocking.
I ordered the book last night.
I have enjoyed this series very much; I too will buy the book.
Thanks for featuring this beautiful writing, Dr. Coyne.
It’s good that the peregrine falcon was saved, but I have to wonder how much genetic diversity they have left at this point. Their numbers got pretty low, didn’t they? Are they in the same position as cheetahs now?