Fractal structure of sequential behaviour patterns: An indicator of stress

The detection of stress arising from parasitic infection by Sarcoptes scabieis and from pregnancy is explored, using a fractal analysis of head lifting behaviour and feeding-non-feeding activity sequences in female Spanish ibex, Capra pyrenaica, under natural conditions. Because organisms under stress increase their metabolic rate and, in consequence, energy consumption, it follows that stress will, generally, lead to a reduction in complexity (fractal dimension) of exploratory behaviour. In the present study the fractal dimension of the three measures of complexity used declined with stress, both from pregnancy and from parasitic infection. This observation provides a new and effective way to assess the general state of animals' health in the field, without the need for capture and handling. (C) 1996 The Association for the Study of Animal Behaviour