ecology, not their habitat, that provides the relevant perspective. From that perspective, the significance of physical structures and routine procedures, as well as infrequent environmental events, will be different from the significance based on the habitat perspective.

How does one approach the captive environment from the ecologic perspective of the animals? Professional judgment, empathy, and intuition are indispensable aids; but they are also very fallible guides and cannot always substitute for more reliable and objective kinds of information.

At the most basic level, birds and mammals—indeed, all animals—have fairly strict requirements with respect to nutrients, water, ambient temperature, humidity, illumination, background noise, and light-dark cycles. Although specific recommendations for dealing with those aspects of an animal's ecology in a captive setting are more often based on professional judgment and opinion than on systematic research, their importance for well-being is widely recognized, and they are usually treated straightforwardly as requirements of good husbandry (see NRC, 1985).

Other ecologic characteristics of captive environments are considered less often, although they can have an important influence on stress and distress (Hughes and Duncan, 1988). On the basis of general ecologic considerations, it can be assumed that the following constitute six major dimensions that are relevant to stress and distress for species housed in a captive environment: relations with conspecifics, predator-prey relations, shelter, spatial architecture, feeding and foraging, and environmental events. Each is discussed in some detail below.

RELATIONSHIPS WITH CONSPECIFICS

Other members of the same species as a given animal usually have significant influences on stress and distress in the animal. The nature of those influences varies widely among species and among individuals within species. Age, sex, and early experience have powerful effects on the extent to which animals will seek, tolerate, or be distressed by the close presence of other members of their species. In many species, seasonal and other cyclic variations in the reproductive state of an animal can affect its social tolerance and sociability.

In determining the potential contribution of social factors to stress and distress, one must consider social space and crowding, deprivation, and social stimulation.

Social Space

The tendency of animals to space themselves in relation to each other is a general feature of social behavior (Waser and Wiley, 1979). The most common means of establishing and maintaining social spacing are overt aggression (e.g., biting and scratching) and aggressive displays (e.g., threat postures and vocaliza-



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