on the basis of any single criterion, such as body weight or dimension. Use of legal cage sizes will not always meet an animal's behavioral requirements. Species that normally move by brachiation (swinging from hand to hand while hanging from supports) or vertical leaping and clinging require substantially different cage designs from conventional quadrupedal striders even if all are of similar body weight. Cage design should reflect units of usable space, that is, space in the cage through which the animal can move. For example, a high glass-walled cage with no vertical perches or climbing structures might look like a two-dimensional environment to its inhabitants whereas a smaller cage, with a smaller floor area and multiple climbing surfaces, might provide more usable space for many nonhuman primates.
Species-typical behavior can be promoted by various aspects of cage design. There should be sufficient space and furnishings, and they should be allocated and placed in a manner that supports basic locomotor patterns and postural adjustments. Special additions to a cage, such as feeding devices, can be placed so as to foster species-typical posture and locomotion. Features of the environment that appeal to humans (such as vertical smooth walls, tidy floors, minimal odors, and soft toys) are not necessarily conducive to the well-being of all nonhuman primates. For example, soft toys might be suitable for infants of some species but dangerous to adults that might try to eat the toys.
When animals are housed socially, the committee believes the spatial requirements of the group need not be calculated by assessing the spatial requirements for one animal to express normal postures and locomotion and multiplying by the number of animals. For example, if housing needs to be 2 m high to permit brachiation, a cage for two animals does not need to be 4 m high. Likewise, floor areas need not be simple multiples. In fact, for arboreal species that normally flee up and spend most of their time climbing, floor area might be secondary to vertical space in providing for postural and locomotor opportunities. The volume of usable space could be the appropriate dimension to consider, and individual animals must have sufficient usable space to express normal postures and locomotion when the space occupied by each cage companion is taken into account. When two animals are housed together by interconnecting their cages, greater spatial opportunities exist for both than when each is housed in its separate cage. Thus, modification of current cage size regulations ought to be considered. Ten animals might not require 10 times the floor space of a single animal to ensure adequate space for normal postures and locomotion, but some animals might need more space than others (NRC 1996), for example, for fleeing from the aggression of dominant animals (old, sedentary, or infirm animals might use less space than younger animals).
We agree strongly with Subpart D, paragraph 3.80(c) of the Animal Welfare Standards, which states that "innovative primary enclosures not precisely meeting the floor area and height requirements provided in paragraphs (b)(1) and (b)(2) of this section, but that do provide nonhuman primates with a sufficient