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 betwe en successive changes of the direction of motion. Here we study the tempora l behaviour of nesting gilts. The time spent by a gilt in a given form of a ctivity has a power law probability distribution without a finite average. Further analysis reveals intermittent occurrence of certain periodic behavi oural sequences which are responsible for the scaling behaviour and indicat es the existence of a critical state. This is in close analogy with tempora l sequences of velocity found in turbulent flows, where random and regular sequences alternate and form an intermittent sequence. The source of this c omplex behaviour can come only from the neural system forced by hormonal st imulus due to nesting instincts. This is the first carefully examined case, where complex scaling behaviour of animals is related to the self-organiza tion and possibly to some unstable critical state of the nervous system. (C ) 2000 Elsevier Science B.V. All rights reserved.