such as television can especially benefit animals housed in single cages. Mirrors are also a potential form of enrichment, specifically for animals that display an understanding of self-recognition, such as non-human primates. In addition to using mirrors to reflect the animal's own image, mirrors can also be angled so the animal is able to see normally out-of-sight areas of the holding area. Enclosures in modern zoos are often designed to facilitate environmental enrichment. For example, the Denver Zoo's exhibit Predator Ridge allows different African carnivores to be rotated among several enclosures, providing the animals with a differently sized environment. Auditory enrichment In the wild, animals are exposed to a variety of sounds that they normally do not encounter in captivity. Auditory enrichment can be used to mimic the animal's natural habitat. Types of nature-based auditory enrichment include rain forest sounds and con-specific vocalizations. The most common form of auditory enrichment is music, whose principal stems primarily from its benefit to humans. The benefits of classical music have been widely studied in animals, from sows to non-human primates. Studies have also looked at various other genres, such as pop and rock, but their ability to provide effective enrichment remains inconclusive. Most types of music that are selected for enrichment are based on human preferences, causing anthropomorphic biases that may not translate to other animals. Therefore, music that is specifically attuned to the animal's auditory senses could be beneficial. Species-specific sounds require further research to find what pitch, frequency, and range is most suitable for the animal. Active enrichment Active enrichment often requires the animal to perform some sort of physical activity as well as direct interaction with the enrichment object. Active enrichment items can temporarily reduce stereotypic behaviors as their beneficial effects are usually limited to the short periods of active use. Food-based enrichment Food-based enrichment is meant to mimic what a captive animal would do in the wild for food. This is extremely important because in the wild, animals are adapted to work hard for what they eat. A lot of time and energy is spent finding food, which is why this tactic is used to make it more challenging for the animal rather than just feeding it simple food. Feeding enrichment techniques causes the animal to indulge in natural, active behaviors that allow for more stimulation and prevents boredom. This form of enrichment forms active behaviors that can also