Murmuration of starlings, the type of behaviour that boids was designed to simulate
Source: YouTube

Boids, a shortened version of “bird-oid object”,[1] is a computational model of flocking behaviour proposed by the computer graphics specialist Craig Reynolds in a paper published in 1987, which he first demonstrated in 1986.[2] Reynolds formally defined flocking as “polarised, non-colliding, aggregate motion”, and his fundamental idea was that rather than scripting the behaviour of each bird in a simulated flock – or fish in a shoal, or animal in a herd – their overall behaviour would emerge if every individual followed three simple rules, without anything in overall control:[2]

  • Separation: steer to avoid crowding local flockmates
  • Alignment: steer towards the average heading of local flockmates
  • Cohesion: steer to move towards the average position of local flockmates

Reynolds’ approach was a significant step forward from the traditional techniques previously used in computer animation. The first film created using his new algorithm was Stanley and Stella in: Breaking the Ice (1987), followed by Tim Burton’s film Batman Returns (1992), with computer-generated bat swarms and armies of penguins marching through the streets of Gotham City.[3]

Flocking, or Particle Swarm Optimization as it is now more formally known, has since become an area of study in several fields of research, including statistical physics, control theory and robotics.[4]



Bajec, Iztok Lebar, and Frank H. Heppner. “Organized Flight in Birds.” Animal Behaviour, vol. 78, no. 4, Oct. 2009, pp. 777–89,
Banks, Alec, et al. “A Review of Particle Swarm Optimization. Part I: Background Development.” Natural Computing, vol. 6, no. 4, July 2007, pp. 467–84,
Ramos, Rita Parada, et al. “Evolving Flocking Behaviour in Embodied Agents Based on Local and Global Application of Reynolds; Rules.” PLoS ONE, vol. 14, no. 10, 2019,
Reynolds, Craig. Flocks, Herds and Schools: A Distributed Behavioral Model. SIGGRAPH ’87: Proceedings of the 14th Annual Conference on Computer Graphics and Interactive Techniques. no. 4, 1987, pp. 25–34,

External links