until the week before estrus. Most can be kept as pairs for breeding, and even usually incompatible males can be safely placed with an estrous female. Males, however, should be removed from the room when females are ready to deliver and not returned until infants are welldeveloped. If left with a female, a male will cannibalize infants and, if left in the same room, might so stress a female that she will attack her own infants. Gestation periods are 5.5–6 months in lorises and 4.5 months in galagos.
Although tarsiers will breed in captivity, they rarely survive the first week. Gestation is 6 months, and infants can weigh nearly 25% of the adult female's weight. It is thought that the failure of infants to thrive is due to dietary inadequacy.
Little work on lemur cognition has been published, and the general impression is that these animals are less ingenious than other primates. Nevertheless, they display similar abilities in reconciliation after fighting and have complex vocal repertoires. Housing of dwarf and mouse lemurs can be enriched by constructing cages with many internal branches and chambers that are connected by tunnels so that animals can range throughout considerable space and have both contact with conspecifics and the ability to avoid them. Enrichment devices in the form of puzzles excite little interest in lemurs. However, food puzzles that require efforts in foraging do seem to attract their interest.
The indrids will make use of swings and ropes and respond to food extraction puzzles. Although often passive, sifakas can be ingenious and manipulative when challenged in searching for food.
The aye-aye has a more convoluted brain than other prosimians and well-developed foraging capacities that involve coordination of the senses. Hearing is extremely acute, and the third digit on the forelimb is elongated and specialized for probing and percussive tapping. Enrichment can be provided through puzzle feeders, logs that contain grubs, and relatively frequent cage-furniture rearrangement.
Lorisids are inquisitive about their surroundings and seem to enjoy novel objects, such as wire mazes that contain fruit. Having live prey to hunt also greatly interests lorisids. Slender lorises will catch fish in water and stalk insects, birds, and small mammals. Gum-arabic feeders and such unusual food items as yogurt, eggs, and novel insects elicit the attention of all lorisines.
Tarsiers seem to be lacking in responsiveness or inquisitiveness, but they do seem to appreciate complex cage interiors. Providing the widest possible variety of prey items also elicits fuller expression of their hunting regimen. Housing of tarsiers alone is inadvisable because it leads to inactivity. Same-sex pairs can show hostility, but groups of as many as six or seven can be formed without apparent conflict.