Behavioral enrichment, also called environmental enrichment, is an animal husbandry principle that seeks to enhance the quality of captive animal care by identifying and providing the environmental stimuli necessary for optimal psychological and physiological well-being. The goal of environmental enrichment is to improve or maintain an animal's physical and psychological health by increasing the range or number of species-specific behaviors, increasing positive utilization of the captive environment, preventing or reducing the frequency of abnormal behaviors such as stereotypies, and increasing the individual's ability to cope with the challenges of captivity. Environmental enrichment can be beneficial to a wide range of vertebrates and invertebrates such as land mammals, marine mammals, birds, amphibians, reptiles, octopuses and spiders.
Environmental enrichment can be offered to any animal in captivity, including:
- Captive animals in zoos and related institutions.
- Animals in sanctuaries.
- Animals used for research
- Animals used for companionship, e.g. dogs, cats, rabbits, etc.
Types of enrichment
Any stimulus which evokes an animal's interest in a positive way can be considered enriching, including natural and artificial objects, scents, novel foods, and different methods of preparing foods (for example, frozen in ice). Most enrichment stimuli can be divided into six groups:
- Environmental; enhancing the animals' captive habitat with opportunities that change or add complexity to the environment.
- Feeding; making feeding more challenging. Different methods of food presentation encourage animals to investigate, manipulate and work for their food as they would in non-captive environments.
- Manipulation; providing items that can be manipulated by the paws, feet, tail, horns, head, mouth, etc. This promotes investigatory behaviour and exploratory play.
- Puzzles; requiring an animal to solve simple problems to access food or other rewards.
- Sensory; stimulating animals' senses: visual, olfactory, auditory, tactile, and taste.
- Social; providing the opportunity to interact with other animals, either conspecifics or interspecifics.
- Training; training animals with positive reinforcement or habituation.
Elaborate systems of food presentation have been developed (e.g. presenting dead rats for wildcats in a Swedish zoo) and computer programmed devices which allow the animals in the enclosure to search for prey as they would in their natural environment.
It can be argued that a stimulus may be considered enriching even if the animal's reaction to it is negative, such as with unpleasant scents, although stimuli that evoke extreme stress or fear should be avoided, as well as stimuli that can be harmful to the animal. A contrary point of view is that for environmental enrichment to be considered successful, it should promote only positive behaviours.
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 different sized environment and exposing them to each other's scents.
Assessing the success of environmental enrichment
A range of methods can be used to assess which environmental enrichments should be provided. These are based on the premises that captive animals should perform behaviours in a similar way to those in the ethogram of their ancestral species, animals should be allowed to perform the activities or interactions they prefer, i.e. preference test studies, and animals should be allowed to perform those activities for which they are highly motivated, i.e. motivation studies.
The success of environmental enrichment can be assessed quantitatvely by a range of behavioral and physiological indicators of animal welfare. In addition to those listed above, behavioral indicators include the occurrence of abnormal behaviours (e.g. stereotypies, cognitive bias studies, and the effects of frustration. Physiological indicators include heart rate, corticosteroids, immune function, neuorobiology, eggshell quality and thermography.
The 1985 amendments to the United States Animal Welfare Act amendments directed the Secretary of Agriculture to establish regulations to provide an adequate physical environment to promote the psychological well-being of primates and exercise for dogs. Subsequent standards for nonhuman primate environmental enhancement (including provisions for social grouping and environmental enrichment) are included under Section 3.81 in the Animal Welfare Regulations (9 CFR). Concepts relating to behavioral needs and environmental enrichment are also incorporated into the standards for marine, flying, and aquatic mammals.
- Shepherdson, D.J. (1998) “Tracing the path of environmental enrichment in zoos” in Shepherdson, D.J., Mellen, J.D. and Hutchins, M. (1998) Second Nature – Environmental Enrichment for Captive Animals, 1st Edition, Smithsonian Institution Press, London, UK, pp. 1 – 12.
- Young, R.J. (ed.), (2003). Environmental Enrichment for Captive Animals. Universities Federation for Animal Welfare (UFAW), Potters Bar, Herts.
- Sheperdson, D.J., Mellen, J.D. and Hutchins, M. (eds)., (1998). Second Nature: Environmental Enrichment for Captive Animals. Smithsonian Institution Press. Washington, D.C.
- Nicol, C.J. (2007). "Environment enrichment for birds". Retrieved April 9, 2013.
- Hurme, K., Gonzalez, K., Halvorsen, M., Foster, B., Moore, D. and Chepko-Sade, D., (2003). Environmental enrichment for Dendrobatid frogs. Journal of Applied Animal Welfare Science, 6: 285–299 
- Hawkins, M. and Willemsen, M. (2004). "Environmental enrichment for amphibians and reptiles". Retrieved April 9, 2013.
- "Octopus enrichment program". Smithsonian National Zoological Park. Archived from the original on 14 June 2006. Retrieved 2006-06-11.
- Carduccia, J.P. and Jakobb, E.M., (2000). Rearing environment affects behaviour of jumping spiders. Animal Behaviour, 59: 39–46 
- Maple TL (2007). "Toward a science of welfare for animals in the zoo" (PDF). J Appl Anim Welf Sci 10 (1): 63–70. doi:10.1080/10888700701277659. PMID 17484680.
- Ron Hines, D.V.M. (2006-04-24). "Synopsis of the Environmental Enrichment Program of 2nd Chance Sanctuary". Archived from the original on 10 June 2006. Retrieved 2006-06-11.
- Sherwin, C.M. (2007). "Validating refinements to laboratory housing: asking the animals.". Retrieved April 9, 2013.
- Hubrecht, R. (1995). Dogs and dog housing. In, Smith, C.P. and V. Taylor (Eds) Environmental Enrichment Information Resources for Laboratory Animals. Universities Federation for Animal Welfare (UFAW), Potters Bar, Herts. pp. 49-62 
- Dawkins, M.S., (1989). Time budgets in red junglefowl as a baseline for the assessment of welfare in domestic-fowl. Applied Animal Behaviour Science, 24: 77-80. doi:10.1016/0168-1591(89)90126-3
- Sherwin, C.M. and Glen, E.F., (2003). Cage colour preferences and effects of home-cage colour on anxiety in laboratory mice. Animal Behaviour, 66: 1085-1092
- Sherwin, C.M., (2004). The motivation of group-housed laboratory mice, Mus musculus, for additional space. Animal Behaviour, 67: 711-717. doi:10.1016/j.anbehav.2003.08.018
- Mason, G.J., (1991). Stereotypies - A critical review. Animal Behaviour, 41: 1015-1037. doi:10.1016/S0003-3472(05)80640-2
- Claes, A., Attur Shanmugam, A. and Jensen, P. (2010). Habituation to environmental enrichment in captive Sloth Bears-effect on stereotypies. Zoo Biology, 29: 705-714. doi:10.1002/zoo.20301
- Mendl, M., Burman, O.H.P., Parker, R.M.A. and Paul, E.S., (2009). Cognitive bias as an indicator of animal emotion and welfare: Emerging evidence and underlying mechanisms. Applied Animal Behaviour Science, 118: 161–181
- Duncan, I.J.H. and Wood-Gush, D.G.M., (1971). Frustration and aggression in the domestic fowl. Animal Behaviour, 19:500–504
- Zimmerman, P.H., Lundberg, A., Keeling, L.J. and Koene, P., (2003). The effect of an audience on the gakel-call and other frustration behaviours in the laying hen (Gallus gallus domesticus). Animal Welfare, 12: 315–326
- Kemppinen, N., Hau, J., Meller, A., Mauranen, K.,Kohila, T. and Nevalainen, T., (2010). Impact of aspen furniture and restricted feeding on activity, blood pressure, heart rate and faecal corticosterone and immunoglobulin A excretion in rats (Rattus norvegicus) housed in individually ventilated cages. Laboratory Animals, 44: 104-112
- Laws, N., Ganswindt, A., Heistermann, M., Harris, M., Harris, S. and Sherwin, C., (2007). A case study: fecal corticosteroid and behavior as indicators of welfare during relocation of an asian elephant. Journal of Applied Animal Welfare Science, 10: 349-358. doi:10.1080/10888700701555600
- Martin L.B., Kidd, L., Liebl A.L. and Coon, C.A.C., (2011). Captivity induces hyper-inflammation in the house sparrow (Passer domesticus). Journal of Experimental Biology, 214: 2579-2585. doi:10.1242/jeb.057216
- Lewis M.H., Presti M.F., Lewis J.B. and Turner, C.A., (2006). The neurobiology of stereotypy I: Environmental complexity. In Stereotypic Animal Behaviour: Fundamentals and Applications to Welfare, G. Mason and J. Rushen (Editors). CABI. pp. 190-226. doi:10.1079/9780851990040.0190
- Hughes, B.O., Gilbert, A.B. and Brown, M.F., (1986). Categorisation and causes of abnormal egg shells: relationship with stress. British Poultry Science, 27: 325-337
- Wilcox, C.S., Patterson, J. and Cheng, H.W., (2009). Use of thermography to screen for subclinical bumblefoot in poultry. Poultry Science, 88: 1176-1180. doi:10.3382/ps.2008-00446
- Richard Crawford (2007). "A Quick Reference to the Requirement for Environmental Enhancement for Primates Under the Animal Welfare Act". Archived from the original on 20 November 2007. Retrieved 2007-11-06.
- Richard L. Crawford (2007). "A Quick Reference to the Requirement for the Exercise of Dogs Under the Animal Welfare Act". Archived from the original on 20 November 2007. Retrieved 2007-11-06.
- "U.S. Laws, Regulations and Guidelines for Environmental Enhancement of Nonhuman Primates". USDA, Animal Welfare Information Center. 2006. Retrieved 2007-11-06.
- Kulpa-Eddy, Jodie A.; Taylor, Sylvia; Adams, Kristina M. (2005), "USDA Perspective on Environmental Enrichment for Animals", ILAR Journal (Washington, DC: Institute for Laboratory Animal Research) 26 (2): 83–94, ISSN 0018-9960
|Wikimedia Commons has media related to Behavioral enrichment (animals).|
- Laboratory Animal Refinement Database
- Animals in Laboratories (awionline.org)
- 3R Research Foundation Switzerland (forschung3R.ch)
- Animal Welfare Information Center (nal.usda.gov)
- The Shape of Enrichment selected articles on enrichment for zoo animals.
- Environmental Enrichment for Pet Cats (ASPCA)
- Environmental Enrichment for Pet Dogs(ASPCA)
- Environmental Enrichment for Horses(ASPCA)