for protecting the stimulus and the subject population from one another (e.g., holding cages). 
Additional attention should be paid to the stimulus animal's social status if it is a conspecific. 
Once the exposure is over, the stimulus animal must either be returned to its original location 
or be incorporated into the subject population. Novak et al. (1998) describe methods for 
capture, sedation, and marking of free-ranging animals. 
ENCLOSURES 
A number of species are housed in large groups in enclosures outdoors (e.g., ungulates, 
rodents, and canids), in zoological parks, or in laboratories (e.g., nonhuman primates). 
Observation of these animals may occur from blinds, catwalks, or other areas that are 
separated from the animals, or the observers may move freely among the animals. When 
observers and animals can intermingle, there are risks to the health and welfare of both 
animals and observers. Thus, observers should be knowledgeable about the behavior of the 
species they are observing. For example, they should be aware of flight distances and not 
inadvertently corner animals. Before they are allowed to observe animals independently, they 
should receive training from experienced, on-site personnel on how to respond to particular 
individuals and particular situations and how to protect themselves from danger. Observers 
need to be screened for the presence of diseases that may be highly transmissible to the 
animals. They should also receive prophylactic inoculations and tests (e.g., against rabies, 
tuberculosis) where relevant. 
Animals housed in large social groups require planning for their separation from the group if 
they become ill or injured, and for the return to the group. In some primate species, such re- 
introductions can be problematic depending on the animal's sex and rank, the length of the 
time away from the group, and the initial cause of the removal. 
Ethologists often incorporate key ecological elements into their laboratories. Arboreal species 
are usually given access to climbing surfaces and structures; scent-marking species are 
provided with relevant marking surfaces that are not sanitized in every cleaning cycler and 
burrowing species are housed under natural covers such as hay. 
Sanitation objectives need not conflict with "naturalizing" the animal's environment (e.g., 
items made of wood should be spot cleaned and removed when worn). For some rodent 
species, the transfer of a small amount of soiled bedding to clean cages may actually improve 
reproductive success. Furthermore, scent-marking surfaces should not be routinely cleaned 
because this often creates the situation of a "strange environment," and for some animals the 
result is excessive scent-marking behavior and physiological stress. 
WILD-CAUGHT ANIMALS AS RESEARCH SUBJECTS 
Wild-caught animals are studied in captivity to observe behavior under controlled conditions. 
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