My eight-month-old kitten's favorite toy isn't a ball, or even a catnip-stuffed toy mouse. It's a laser pointer—one of those handy little devices that have become so popular with lecturers of all sorts. I shine the little red dot on the floor and he goes crazy, chasing it around until he's panting and I feel compelled to put an end to the fun. My two-and-a-half year old cat, on the other hand, would much rather lounge quietly in a paper bag than expend the energy it takes to hunt a fast-moving dot that he's too slow to catch anyway. Is this difference in play preferences related to age? Is it just a product of differences in their dispositions?

Although laser pointers and paper grocery bags are hardly items that cats would encounter in the wild, they do allow housecats to express natural behaviors—in this case, hunting and hiding. This example points out two important aspects of environmental enrichment: the fact that the most effective enrichment devices are generally those that stimulate an animal's natural instincts, and that preferences in enrichment devices can differ considerably not only from species to species but also between members of the same social group. With these ideas in mind, this issue focuses on some of the enrichment options available for captive nonhuman primates.

There is currently a wide range of enrichment options available for nonhuman primates (p. 37). Some of these are toys usually associated with other species, such as canine chew toys, while other items, such as mirrors and platforms, might not normally be considered toys at all. In addition to animals occupied, these devices can potentially offer direct health benefits, as with chew toys that can help clean teeth and stimulate gums, while others help nonhuman primates to fulfill their instinctive desire to forage and work for food.

Howell et al. (p. 31) explore an alternative means of enrichment for nonhuman primates, and present the results of a study conducted at the Primate Foundation of Arizona (PFA) to determine if music is an effective environmental enhancement for captive chimpanzees. They installed a stereo system that allowed for colony-wide broadcasts of music, ranging from Pavarotti to Dolly Parton to Dido. During the course of the six-month-long study, which involved a total of 57 chimpanzees, the researchers found that the music had a significant effect on the animals' behavior. Low levels of music—especially during the morning hours when PFA staff members carry out most of their husbandry tasks—resulted in a reduced incidence of behaviors associated with agitation and aggression. In addition, the music was associated with increased levels of nonaggressive social behaviors, including grooming.