Scaling and intermittency in animal behaviour

Scale-invariant spatial and temporal patterns have been observed in a large variety of biological systems. It has been argued that animals in general might perform Levy flight motion with power law distribution of times between successive changes of the direction of motion. Here we study the temporal behaviour of nesting gilts. The time spent by a gilt in a given form of activity has a power law probability distribution without a finite average. Further analysis reveals intermittent occurrence of certain periodic behavioural sequences which are responsible for the scaling behaviour and indicates the existence of a critical state. This is in close analogy with temporal sequences of velocity found in turbulent flows, where random and regular sequences alternate and form an intermittent sequence. The source of this complex behaviour can come only from the neural system forced by hormonal stimulus due to nesting instincts. This is the first carefully examined case, where complex scaling behaviour of animals is related to the self-organization and possibly to some unstable critical state of the nervous system. (C) 2000 Elsevier Science B.V. All rights reserved.