Behavioral enrichment

Visual enrichment is typically provided by changing the layout of an animal's holding area. The type of visual enrichment can vary, from something as simple as adding pictures on walls to videotapes and television. Visual enrichment such as television can especially benefit animals housed in single cages.[13]

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.[13]

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.

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.[13]

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[14] to non-human primates.[15] Studies have also looked at various other genres, such as pop and rock, but their ability to provide effective enrichment remains inconclusive.[15][16][17] Most types of music that are selected for enrichment are based on human preferences, causing anthropomorphic biases that may not translate to other animals.[17] Therefore, music that is specifically attuned to the animal's auditory senses could be beneficial.[18] Species-specific sounds require further research to find what pitch, frequency, and range is most suitable for the animal.

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.[19] Feeding enrichment techniques causes the animal to indulge in natural, active behaviors that allow for more stimulation and prevents boredom.[19] This form of enrichment forms active behaviors that can also help with not only a captive animal's mental health, but the animal's physical health.[19]

For example, food can be hidden and spread across an enclosure making the animal actively search for it. Other common manipulable tactile objects include rubber toys stuffed with treats. Instead of providing the food directly, foraging devices are useful in increasing the amount of searching and foraging of food, comparable to the amount of time they would spend in the wild.[13] Most food-based enrichment occurs in the context of searching for food, such as cracking open a nut or digging holes in tree trunks for worms.

A structure built for baboons at the Oakland Zoo

Structural Enrichment is when objects are added to an enclosure to mimic an animal's natural habitat. These objects can be switched out occasionally or kept permanently.[20] The environment of captive animals should be switched frequently since their environment in the wild would bring on new objects and exploration. Research into what constitutes the most beneficial and appropriate forms of enrichment must be used when considering the provision of enrichment options, especially for species where natural-like settings may be difficult to achieve.[21] The animal should never become too familiar with their environment because that can cause boredom, no stimulation or stereotypical behavior.[20] Examples of this could be swings or climbing structures.[20] Stones have also been shown to encourage exploratory behavior in Japanese macaques. Interaction with the stones exhibited behaviors such as gathering, rolling in hands, rubbing, and carrying.[13]

Other common forms include cardboard, forage, and even the texture of the food (i.e. hard, smooth, cold, warm).[22]

Olfactory enrichment can stimulate naturalistic behavior, enhance exploration, and reduce inactive behaviors.[23] Olfactory enrichment can be utilized by itself, paired with novel toys, or paired with food-based enrichment. This type of enrichment is most commonly used with species that commonly utilize their olfactory senses in the wild. Although highly beneficial, it is important for researchers to analyze the long-term effects of certain odors on captive animals. Odors can be scattered on a novel toy such as a ball or semi-randomly throughout an enclosure. Various forms of odors can include catnip, odor of conspecific, perfume, feces of a prey species, or spices.

Cognitive enrichment is defined as, improving animal welfare by providing opportunities for captive animals to use cognitive skills for problem solving and providing limited control over some aspects of its environment.[24] In the wild, animals deal with ecological challenges in order to acquire the resources, such as food and shelter, that they require to survive.[25] These challenges arise from interactions with other animals, or through changes to their environment that require the individuals to exercise their cognitive ability and to improve their behavioral strategies.[25] Therefore, these challenges act as an important problem-solving element in the animals' day-to-day lives, and in-turn, increases their overall fitness.[25] The animal anticipates positive benefits from a challenging situation[26] which can directly affect its emotional processes.[27] Cognitive enrichment should be provided in addition to a diverse environment that is already structurally and socially enriched; it goes beyond the basic needs of the animals.[26]

Social enrichment can either involve housing a group of conspecifics or animals of different species that would naturally encounter each other in the wild. Social animals in particular (i.e. most primates, lions, flamingos, etc.), benefit from social enrichment because it has the positive effect of creating confidence in the group.[28] Social enrichment can encourage social behaviors that are seen in the wild, including feeding, foraging, defense, territoriality, reproduction, and courtship.[29]

The most common form of human-interaction enrichment is training. The human and animal interaction during training builds trust, and increases the animal's cooperation during clinical and research procedures. In addition, training sessions have been shown to benefit the welfare of both individually housed animals and communally housed animals by providing cognitive stimulation, increasing social play, decreasing inactivity, and mitigating social aggression during feeding.[30]

Although environmental enrichment can provide sensory and social stimulations, it can also have limited efficacy if not changed frequently. Animals can become habituated to environmental enrichments, showing positive behaviors at onset of exposure and progressively declining with time. Environmental enrichments are effective primarily because it offers novelty stimuli, making the animal's daily routines less predictable, as would be in the wild. Therefore, maintaining novelty is important for the efficacy of the enrichment. Frequently changing the type of environmental enrichment will help prevent habituation.[7]

Usage of more highly advanced enrichment devices, such as computerized devices, requires training. This can lead to issues as training often consists of food as a reward. While food encourages the animal to participate with the device, the animal could associate the device with food. As a result, the interaction with the enrichment would bring about behaviors that are associated with training instead of the desired playful and voluntary behaviors.[47]

The process of producing and providing environmental enrichment usually require a large allocation of time and resources. In a survey,[48] "time taken by animal care staff to complete other tasks" was the most significant factor influencing environmental enrichment provisions and scheduling. Therefore, it is important to develop appropriate environmental enrichment programs that can be effectively carried out with the size of staff and time available.