We have already examined in Chapter 2 the question of stress, and how to recognise it. In this chapter some concrete examples will be discussed. The case of the marsupial quokka (Setonix brachyurus) has already been evoked as an illustration of an animal in mid-summer displaying a significantly modified milieu intérieur (dehydration with elevated plasma osmolality) associated with a maximal deployment of regulatory processes (very high circulating levels of the antidiuretic hormone lysine vasopressin; see Jones et al. (1990) for more details). This combination of a significant deviation of the milieu intérieur from whatever is considered to be the normal or ideal state, despite the activation of homeostatic regulatory processes, will be our leitmotif for identifying cases of stress, and also for measuring their intensity (Bradshaw, 1992a).
An interesting case is the silvereye (Zosterops lateralis), a small (10 g) Australian bird (see Figure 5.1) that has come to be the bane of vignerons in many parts of that country. These birds from time to time descend in their thousands to devastate grape crops in late summer, usually just before the harvest. The case is unusual for Australia, where most of the pests (such as the fox, cat and rabbit) are of European origin, and has necessitated a detailed study of this indigenous bird's ecophysiology (Rooke et al., 1983, 1986; Rooke, 1984).