fostering paradigm. First, the time of cross-fostering is generally critical to its success. For 
some species, fostering must occur within the first day or two of life (e.g., voles). When the 
timing is unknown, offspring should be monitored carefully for signs of rejection or neglect. 
Even when parents care for offspring, continued monitoring for signs of malnourishment may 
be necessary. Second, there may be significant health risks in housing certain species 
together. Finally, cross-fostering can lead to altered species-typical behavior in adulthood 
(e.g., in terms of mating preferences and patterns of parental care). The study of behavioral 
differences attributable to fosterers may be the focus of research, but cross-fostered animals 
may be unsuitable for routine use in breeding colonies because their offspring may differ 
substantially from the species norm. 
SEPARATION FROM CONSPECIFICS DURING DEVELOPMENT 
Some research involves separating animals from conspecifics during development. In some 
cases, the separation is necessary in order to provide the animal with alternative rearing 
environments (e.g., rearing nonhuman primates with inanimate surrogates and/or peers) or 
with controlled stimulation from conspecifics (e.g., use of playbacks in song acquisition in 
passerine birds). In other cases, the process of separation is of interest (e.g., mother-infant 
separation in nonhuman primates). 
When animals are separated from parents through experimental protocol, the investigator and 
the animal care staff must assume responsibility for rearing the offspring. Adequate attention 
must be paid to the temporal provisioning of food, actual food intake, nutrition, warmth, and 
other biological needs. Consideration must also be given to the possible stress produced by 
the loss of companions. In this regard, both the timing and the type of separation may be 
crucial. Offspring that are separated at birth or shortly thereafter may not yet have formed 
strong social bonds with their parents and peers. In contrast, offspring separated later in 
development may show acute stress followed by depression in response to separation from 
conspecifics (e.g., three-month old rhesus monkey infants separated from their mother). The 
type of separation will also affect the response of the offspring. Separation in which an infant 
is removed from its social group and placed in a new environment by itself may be 
considerably different from separation in which a particular conspecific such as the mother is 
removed from the social group and the infant in question remains behind with the other group 
members. Regardless of the kind of separation, young animals should be monitored closely 
and evaluated regularly. Further, the long-term consequences of any developmental 
separation should be considered, and the long-term care of adversely affected animals should 
be addressed. The above discussion pertains to separation during early development and not 
to removal of juveniles following a natural weaning process, as is the practice of those caring 
for and maintaining rodent and other breeding colonies (Reite, 1987). 
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