advisable not to house these primates in two-tier cages. There are reports of less activity and poorer reproductive performance when animals are housed in the lower tier of a two-tier cage system (Heger and Neubert 1988; Scott 1989). When space is at a premium, narrow, high cages are preferred over wide, low cages placed one on top of the other. An alternative to providing tall cages is to suspend cages from the ceiling, so that there is space between the cage floor and the floor of the room. Covering the cage floor with wood chips or shredded paper substantially increases the use of the floor by common marmosets and cotton-top tamarins (McKenzie and others 1986).

Marmosets and tamarins might be reluctant to retrieve food from the cage floor. If tall cages are used (say, 2 m, or 6.6 ft, high), animals rarely descend to less than 0.5–1 m (1.6–3.3 ft) above the floor. Therefore, food and water should be offered on a feeding platform or in a bowl placed high in the cage and in a position that avoids contamination from feces and urine.

If small cages are used, it is beneficial to provide a large exercise cage for temporary use. One method of increasing the effective space is to use transparent air-conditioning ducting attached to the side of cages (Hearn 1983). Animals can be trained to move voluntarily through the ducting to enter other cages or transport cages, thus minimizing the stress of handling. Animals that are removed from groups because of illness or behavior problems can still be allowed close visual access through the ducting. Finally, a loop of ducting running from one side of the cage around the back or over the top to the opposite side creates a runway that is frequently used by juveniles and subadults in play.

The nature of the furnishings in the cage appears to be even more important than the absolute amount of space in facilitating species-typical behavior. It is desirable to have a variety of wooden or fiber structures in a cage. Branches and ropes allow animals to display manipulative behavior and a range of natural movements, including leaping from branch to branch. Such cage furnishings will need to be replaced every 2–3 months as they wear out (e.g., bark stripped from branches) and as necessary to maintain sanitation. Panels can be used to divide the cage into visually shielded compartments; this allows submissive animals to move out of sight of dominant cagemates. The nest box can be provided with a locking door to double as a transport box when required.

Chemical communication by means of scent marking is important in the sexual and social behavior of all callitrichids (Epple 1986). Branches are the normal substrate for scent-marking with urine and the secretions from specialized scent glands. Animals that are provided only with smooth, nonabsorbent surfaces, such as stainless steel or plastic, scent-mark these surfaces. The sticky, lipid-containing marks coating the surfaces of smooth objects tend to soil the animals' fur.

The amount of scent-marking behavior varies among species and even among individuals of the same species. Therefore, a cage-washing schedule that constitutes a compromise between the need for sanitation and an intact odor environ-

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