The seventh starling (Murmuration)

What do particle physics, statistics and poetry have in common? (includes videos)

Jan 17, 2025

Starling shapes in the evening sky

A large number of starlings congregate at Gretna Green every evening at sunset during the winter months to perform an elaborate aerobatic display before roosting in nearby conifer plantations. It can be quite breathtaking to witness the birds twisting into unusual patterns in the sky. (© Copyright Walter Baxter and licensed for reuse under this Creative Commons Licence.)

This will be my last murmuration piece until next winter (I’m referring to a northern hemisphere winter, by the way, for those who are wondering.) If you like these pieces, then you’ll be disappointed, and if you’re sick of them, well yay, you won’t need to see them for quite a long time then.

Anyone who has looked at the late afternoon sky has seen it: a single, giant shape-shifting creature of the air made up of hundreds, thousands or even tens of thousands of birds wheeling and swirling overhead as they settle in to their communal evening roosts. During migration, birders often gather along coastlines to watch similar spectacles unfold as massive flocks of shorebirds evade hunting peregrine falcons, Falco peregrinus, that pursue them on their arduous journey. Not only do many species of birds move in three-dimensional flocks, but other animals do, too: fish shoal and insects swarm.

This lovely video, which is my absolute favourite murmuration film because the filming and music are exquisitely perfect, and the location is near my original stomping grounds of the Puget Sound in western Washington State, captures many hundreds of thousands of European starlings, Sturnus vulgaris, as they settle in to their evening roost on a winter night:

Visit Sophie Windsor Clive’s Vimeo channel. (Music by Emmett Glynn and Band.)

Rapidly changing shapes of bird flocks inspire us and fill us with wonder: How do they do that? How do so many birds move in three dimensions in such dynamic and tightly-packed aggregations without crashing into each other?

Hypotheses abound. One hypothesis, proposed in the 1930s by British writer and ornithologist, Edmund Selous, went so far as to suggest that bird flocks coordinate their movements through telepathy.

“Surprisingly enough, in an era in which splitting the atom into its tiniest parts has become commonplace for science, obtaining empirical data on large groups of animals moving in three dimensions is still a very difficult task”, write statistical physicists Andrea Cavagna and Irene Giardina, in their paper, “The Seventh Starling” (ref). Dr Cavagna and Dr Giardina study the physics of flocking and other collective animal behaviour at the Centre for Statistical Mechanics and Complexity in Rome, Italy.

Palazzo Massimo alle Terme. (Credit: RyanFreisling/Public Domain.)

After perching atop the Palazzo Massimo at sundown for three winters to film the aerial ballet of flocking starlings, Dr Cavagna and Dr Giardina and their collaborators have learned that these flocks have several basic rules — traffic rules, if you will — to avoid collisions.

“The clearest structural feature is that a bird’s nearest neighbours are typically found at the bird’s sides, rather than ahead or behind the bird, so that the probability that a bird’s nearest neighbour is approximately ahead or behind is very low”, the authors write.

Perhaps the reason is anatomical. Since the bird’s eyes are on the sides of its head, it sees sideways better. Or maybe the birds are keeping a safe distance between themselves and those in front to avoid rear-end collisions — similar to humans driving cars at speed on crowded motorways.

The research team also found that any particular starling’s spatial orientation and velocity correlates with the orientation and velocity of its six closest neighbors, regardless of flock size. But why not five or seven or ...? Dr Cavagna and Dr Giardina think that seven may serve as the cognitive limit for starlings: they simply cannot track the movements of a larger number of neighbours. (Perhaps not coincidentally, humans share this cognitive limitation.)

Nevertheless, starling flocks are ultimately democratic. If any one bird turns or changes speed, so will all the others. Such changes radiate outwards in a wave from the individual to affect the entire flock. Statistically speaking, every individual bird is interconnected within the same dynamic web of interactions.

My favourite poet, Mary Oliver (1935-2019), has a few ideas about starling flocks:

...they are acrobats
in the freezing wind.
And now, in the theater of air,
they swing over buildings,
dipping and rising;
they float like one stippled star
that opens,
becomes for a moment fragmented,
then closes again;
and you watch
and you try
but you simply can't imagine
how they do it
with no articulated instruction, no pause,
only the silent confirmation
that they are this notable thing,
this wheel of many parts, that can rise and spin
over and over again,
full of gorgeous life.
~ excerpted from “Starlings in Winter” by Mary Oliver; Owls and Other Fantasies: Poems and Essays (Beacon Press, 2003 [Amazon UK; Amazon US]).

Source:

Cavagna, A., & Giardina, I. (2008). The seventh starling. Significance, 5 (2), 62–66 | doi: 10.1111/j.1740–9713.2008.00288.x

Additional reading (includes scary mathematical formulae and lots of other details):

Cavagna, A., Cimarelli, A., Giardina, I., Parisi, G., Santagati, R., Stefanini, F., & Viale, M. (2010). Scale-free correlations in starling flocks. Proceedings of the National Academy of Sciences, 107 (26), 11865-11870 | doi:10.1073/pnas.1005766107

Hemelrijk, C., & Hildenbrandt, H. (2011). Some Causes of the Variable Shape of Flocks of Birds. PLoS ONE, 6 (8) | doi:10.1371/journal.pone.0022479

If you would like to find a murmuration near you, contact the nearest Audubon Society office (if you’re in the USA) or Birdlife office (if you’re in the EU). November through January is the best time to witness this spectacle because starlings and other birds only gather together into large flocks in winter.