Enrichment is in the Eye of the Beholder

What is Enrichment?

Animals have evolved and adapted to live in complex environments with a wide variety of engaging stimuli: diverse plants, other animals, sounds, smells, problem-solving scenarios, and dynamic space, just to name a few. The natural history of animals has resulted in the development of species-specific repertoires of highly motivated behaviors, which are behaviors that animals will perform regardless of increasing cost, or even in the absence of appropriate stimuli, as they are important for fitness (Dawkins, 1990).

In captivity, an animal’s environment is more predictable – humans provide regular food and water, facilities protect from predators and disease, and enclosures remain constant day to day. However, lack of stimulation and variation in captivity typically has negative consequences for animals, such as a decrease in the expression of normal behavior, an increase the incidence or severity of unwanted abnormal behaviors, and a reduced ability to cope with behavioral and environmental challenges (FASS, 2010). These negative consequences pose concern for animal welfare, and occur in both domesticated animals (e.g. farm and companion animals) and wild animals housed in captivity (e.g. zoo animals, rehabilitation and reintroduction programs, and research facilities). In order to prevent these negative consequences, caretakers aim to provide enrichment to captive animals.

Meerkat  Enrichment
Foraging enrichment is a popular form of enrichment for many animals, including these grub-loving meerkats. [Source]
Enrichment is loosely defined as any stimuli or activity that promotes positive engagement and variation within an animal’s environment (Markowitz, 1982; National Academy of Sciences, 2011). The goal of enrichment is to improve physical and psychological well-being and encourage animals to display a wider range of naturalistic behaviors, in particular, species-specific highly motivated behaviors (Markowitz, 1982; Swaisgood & Shepherdson, 2005; National Academy of Sciences, 2011).

lizard rock
Structural and sensory enrichment, like this basking rock, are important for this lizard to maintain body-heat in a naturalistic way. [Source]
Enrichment can fall under five main categories (Delfour & Beyer, 2006; Wells, 2009; FASS, 2010):

  1. Sensory (visual, auditory, olfactory, and/or tactile stimulation)
  2. Foraging (food-related, such as a variety of food types or different methods of food delivery)
  3. Structural (size or complexity of enclosure, adding accessories to an enclosure)
  4. Occupational (toys and activities that promote exercise or solvable challenges)
  5. Social (direct or indirect contact with conspecifics, e.g. intraspecies, interspecies, or human interactions)

There are several enrichment types in this picture, can you name them all? [Source]
Why do we care?

Enrichment is important for improving an animal’s welfare, which considers an animal’s health and life expectancy, the expression of highly motivated naturalistic behaviors, and positive affective states (Fraser et al., 1997). Providing enrichment to animals is similar to providing playgrounds, a balanced diet, puzzles, attention, and education for children; all of these factors contribute to a better life (both long and short term) for that individual. Animals provided with greater opportunities for movement and exercise have stronger bones and muscles and improved navigational abilities (Markowitz, 1982; Newberry, 1995; Leggio et al., 2005; Casey-Trott et al., 2017). Foraging enrichment and varied diets promotes balanced nutrition and gastrointestinal health, reduces negative affective states (e.g. boredom, frustration), and increases the expression of foraging behaviors (Shepherdson et al., 1993; Thorne et al., 2005; Schipper et al., 2008; Herrmann et al., 2013). Animals who have access to novel objects and problem solving activities adapt better to change (Meehan & Mench, 2007), have reduced stress levels (Shepherdson et al., 2013), and increased brain development (Kempermann et al., 1997). Enrichment also results in a reduction or prevention of abnormal behavior, such as stereotypic behavior (Shepherdson et al., 2013). Stereotypic behavior is an abnormal repetitive behavior with seemingly no function for the animal (e.g. pacing, weaving, cribbing, etc.) that results from frustration, attempts to cope with stressors in the environment, and/or central nervous system dysfunction (Mason et al., 2006). Enrichment also benefits the overarching goals of certain captive environments, such as making lab animal research and results more biologically relevant and transferrable to humans (Bayne & Würbel, 2014; Grimm, 2018), increasing successful reproduction for captive breeding programs (Damm et al., 2010), and generally promoting positive animal-human interactions (Kry & Casey, 2007; Melfi, 2013).

Since there are so many different kinds of animals and a multitude of ways to enrich these animals, here are some examples:

Chicken dust bath
Species: Chicken (Gallus gallus domesticus)

Normal behavior (natural history): Chickens are a gregarious species, living in flocks and establishing a social hierarchy (or “pecking order”) with dominant and submissive individuals. They spend the majority of their day foraging by pecking at substrate on the ground, as well as dust bathing, a grooming mechanism that removes dirt and oils from their feathers.

Unwanted abnormal behaviors: Without substrate for foraging, chickens will redirect their pecking behavior onto the feathers of other birds. This can cause feather loss, injury, and even death in flock mates. Feather quality also deteriorates when hens are unable to properly dustbathe. Hens will continue to perform “sham” dust bathing behavior, going through the motions of preening and feather ruffling without being able to move substrate through their feathers and actually remove dirt, oils, and insects. Both scenarios result in decreased feather quality and potential injury for the hens.

Enrichment: Provide substrate to hens (e.g. loose wood shavings, sand) to encourage foraging and dust bathing in order to reduce injury to flock mates and promote feather quality.

Enrichment category: Structural

Cat tree
Species: House cat (Felis silvestris catus)

Normal behavior (natural history): Cats are motivated to perform hunting, exploratory, climbing, perching, and scratching behaviors. While sociability is variable amongst domestic cats, they are generally territorial towards other cats.

Unwanted abnormal behaviors: Cats will display aggression towards people and other cats for a variety of reasons, but some common causes are redirected play, predation, or regaining control of resources. This behavior may cause fear and injury in the recipient and indicate frustration in the perpetrator animal.

Enrichment: Provide a cat perch next to a window to encourage climbing, perching, and exploration (i.e. looking outside) behaviors, while allowing two cats or a cat and human to gain physical distance between each other.

Enrichment category: Structural, sensory

Sheep hay
Species: Sheep (Ovis aries)

Normal behavior (natural history): Sheep spend the majority of their day consuming fiber-rich diets by grazing on grasses and forages, then ruminating those fibers (e.g. re-chewing and fermenting) to aid in digestion.

Unwanted abnormal behaviors: When there is a lack of fiber in the diet (e.g. feedlot sheep that are fed energy-rich diets based on corn), sheep perform wool-biting behavior. Sheep bite and potentially ingest the wool from other pen mates, causing wool loss and skin inflammation in the target sheep and potential compact wool masses in the digestive tract of the biting sheep.

Enrichment: Provide more fiber and forage in the diet, such as hay in the feed bunk or grazing pasture outdoors, to promote chewing and rumination behavior.

Enrichment category: Foraging

Species: Laboratory mice

Normal behavior (natural history): Mice are highly social and motivated to burrow in dark, complex environments for shelter and safety from predators.

Unwanted abnormal behaviors: Laboratory mice can often be housed individually, or in very bare environments with no shelters or bedding to nest in. The inability to nest and be with conspecifics can lead to increased stress levels, which can lead to poor immunity and alter the quality of scientific results.

Enrichment: Provide bedding, shelter, and familiar conspecifics to promote natural nesting behavior and the comfort of living in a social group.

Enrichment category: Structural, social


Species: Harbor seal (Phoca vitulina)

Normal behavior (natural history): Harbor seals use problem-solving skills to hunt and feed on a variety of marine life including cephalopods (e.g. squid), crustaceans (e.g. crabs), and fish. They have a unique ability to control their buoyancy so they can hunt for different types of food at different levels of the water column.

Unwanted abnormal behaviors: When harbor seals are in a wildlife rehabilitation setting, they are often fed highly nutritive frozen fish. Fish meals come at predictable times of the day, and are provided by caretakers. This can lead to habituation (or getting used to) and reliance on human presence. However, if seals are to be successful when they are released back into the wild, they need to practice hunting for fish on their own.

Enrichment: Provide underwater puzzle feeders that require seals solve problems in order to get food. This encourages utilization of underwater behaviors and helps avoid habituation to humans

Enrichment category: Occupational, foraging

Species: Blue-fronted Amazon parrot (Amazona aestiva)

Normal behavior (natural history): Amazon parrots are highly social animals; they have a wide vocal repertoire and forage in groups. They also develop bonds with monogamous mating partners who roost (or get together) for afternoon naps.

Unwanted abnormal behaviors: Without appropriate stimulation, Amazon parrots can destructively pluck their own feathers, over-vocalize, and develop other stereotypical behaviors, which are abnormal, repetitive behaviors that can be a sign of chronic stress or boredom (Fraser & Bloom, 1990).

Enrichment: Provide interaction opportunities with conspecifics (other parrots of the same species) or with other species. These interactions can include different animals or even behavioral training with humans.

Enrichment category: Social

Some of these may seem intuitive, but it is important to note that effective enrichment must take into account not only natural history and an animal’s highly motivated behaviors, but also the individual animal. One enrichment stimulus or activity may achieve multiple enrichment categories and may have different effects depending on the species and the individual animal (Delfour & Beyer, 2006; Markowitz, 1982; Wells, 2009).

This means that not all enrichment is created equal!

So when we see a complex environment or novel items in a zoo, shop for a new toy for Fido, or design cage-free environments for farmed chickens, here are some questions we can all use to analyze enrichment:

-Does this increase the animal’s behavioral diversity and positive utilization of the environment?

-What is motivating an animal’s abnormal behavior and how can we use enrichment to reduce those abnormal behaviors? Can this enrichment help the animal cope with challenges?

-Does this increase positive utilization of an animal’s environment?

-Does this improve the animal’s biological functioning, and what part of the animal’s natural history are we trying to promote?

Giving an animal novel objects to interact with or taking a dog to the park does not necessarily improve their welfare with one quick fix. Understanding animal perception, natural history, and individuality are the key components to successful, meaningful enrichment and improved well-being of animals in all settings!

Karli Rice Chudeau is a 1st year PhD student in the Animal Behavior Graduate Group at UC Davis in Dr. Jason Watter’s lab. Her research interests began when examining the effects of enrichment during her master’s program at California State University San Marcos. Karli now studies how to assess welfare and use behavioral interventions in wildlife rehabilitation settings to improve reintroduction success, specifically with pinnipeds.

Allison Pullin is a 1st year PhD in the Animal Behavior Graduate Group at UC Davis in Dr. Maja Makagon’s lab. She is broadly interested in correlating behavior with bone health in farmed chickens raised for egg production (i.e. laying hens), specifically using accelerometers to assess the role of early life environmental complexity in spatial navigation for cage-free laying hens.


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