Information shared by Dr Kate Durrant
If you have never seen the dazzling beauty of a starling (Sturnus vulgaris) flock circling over their roost in the evening, it’s one of nature’s mesmerising sights. There used to be a ‘Starling Hotline’ in Somerset that you could call and find out where they would appear that evening, but it is sadly defunct. The most impressive (and reliable) starling flocks are found in Rome, where the locals love the displays, but hate the mess from the droppings of thousands of birds. Once you see footage of this display you will immediately wonder: how do they do it? How do they bunch and scatter, wheel and turn in perfect synchrony? How do they avoid crashing into each other at high speed and plummeting to the pavement?
The complex social behaviour of animals, like that seen in starling flocks is studied in the field of ‘complexity science’. Researchers have shown that complexity arises from interactions of individuals with nearby neighbours only. So, for example, instead of coordinating with the whole flock, a starling only has to keep track of its three nearest neighbours, who keep track of theirs and so on. By combining theoretical models and empirical data, this approach has increased our understanding of animal societies but studies used mostly social insects, like locusts in a swarm. Birds fly very differently to insects, in particular their tendency to bank and roll on turns. Recently, these flocking manoeuvres have been studied by HD video-recording and stereo photography in Rome. These films of flocks were modelled mathematically by researchers to try and mimic the patterns found in the air, but they often did not produce the same complex, shifting patterns seen in the images. Recent work by Hildenbrandt et al. improved on previous models by using the usual rules for coordination with neighbours but added a number of specifics of starling behaviour, namely rules based on coordination with only very close-by neighbours, on simplified aerodynamics for their flight, including those banking turns, and on the fact that displaying starlings remain above their roosting area. The new model, called ‘StarDisplay’, produces patterns remarkably similar to the filmed flocks, and also produces individual flight patterns that match individuals tracked in flocks on HD films and in stereo photographs. It’s a beautiful combination of complex modelling and empirical evidence from imaging. This new model enhances our understanding of this complex behaviour and can now be applied to other flocking bird species to understand how they move en masse.
Hildenbrandt, H., Carere, C., and Hemelrijk, C.K. 2010. Self-organized aerial displays of thousands of starlings: a model. Behavioural Ecology 19: 10.1093/beheco/arq149