Vigilance, Alarm Responses and an Early Warning System

Abstract

Most animals must not only successfully exploit limited resources, they must also avoid becoming the exploited limited resource of predators and competitors. Both finding limited resources and avoiding predation and exploitation, however, may require considerable investment of time and energy in scanning the environment, because resource availability and encounters with predators and competitors tend to be unpredictable in time and space. The need to scan can seriously constrain an animal’s ability to carry out important maintenance activities such as feeding and sleeping (e.g. Powell 1974, Kacelnik et al. 1981, Barnard and Brown 1981, Lendrem 1982, 1984). Factors which enable animals to modify their investment in scanning are therefore likely to influence their behavioural efficiency and thus reproductive potential. One which we have already seen has an important effect on time and energy budgeting, especially with regard to vigilance, is grouping behaviour (see Chapters 1 and 6, also Barnard 1985). The relationships between grouping behaviour, scanning and responsiveness to alarm stimuli, however, are not necessarily straightforward.