monitoring can often be performed in social groups by means of totally implantable telemetric 
devices (Pauley and Reite, 1981), and implantable osmotic minipumps can be used to deliver 
pharmacological agents in animals living in social groups. 
MOTHER-INFANT REARING 
Macaque monkey infants raised exclusively with their mothers without additional social 
experience may exhibit species-typical social behaviors, but there is some evidence that such 
individuals may also exhibit excess or inappropriate aggressiveness (Mason, 1991; 
Woolverton et al., 1989). These behaviors may result from inadequate contingent social 
behavioral feedback and could also compromise the ability to extrapolate data from such 
subjects to socially reared individuals, and complicate breeding programs dependent upon 
these animals. Such infants can be removed from their mothers when they are able to feed on 
their own, although they will exhibit a separation reaction, with both behavioral and 
physiological components, if they are separated at much less than a year of age. They will 
generally be socially competent adults, although possibly exhibiting atypical aggressiveness. 
SOCIAL MANIPULATIONS: EXPOSURE TO UNFAMILIAR ANIMALS 
Much of the ethological literature is focused on the reactions of animals to members of their 
own or other species. This research runs the gamut from studies of breeding behavior or 
group formation to those that examine communication processes. Animals may be exposed to 
other conspecifics or to specific attributes of those conspecifics such as their odors or 
vocalizations. Welfare considerations will vary depending upon both the context and the 
extent of the exposure. For example, when the exposure occurs between two or more 
unfamiliar animals, care should be taken to minimize the risk of aggression and injury. In 
some cases, bringing unfamiliar animals together may require the use of introduction cages or 
other techniques to provide a period of familiarization under controlled conditions. For 
example, creating breeding pairs of some rodent species may require more effort than merely 
placing the animals in the same cage. To eliminate aggression, males can be placed in a small 
mesh introduction cage within the home cage of the female and then released several hours 
later (as appropriate for the species and individuals). 
MIXED SPECIES INTERACTIONS 
Occasionally different species may be housed together. Primates can be reared in mixed 
species environments for economic as well as for scientific reasons. The African savannah is a 
mixed species environment, as are many modern zoos. Compatibility of species is important, 
and mixed species offspring may occur, which may or may not be desirable. One of the more 
common procedures is to cross-foster young to the parents of a different species in an attempt 
to unravel genetic and environmental influences on behavior. This approach has been used to 
study the acquisition of song in birds, behavioral development in rodents, and patterns of 
aggression and reconciliation in monkeys. Several cautions should be noted in the cross- 
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