Sensory stimulation as environmental enrichment for captive animals: A review

In the wild, animals are exposed to an ever-changing array of sensory stimuli. The captive environment, by contrast, is generally much more impoverished in terms of the sensory cues it offers the animals housed within. In a bid to remedy this, and promote better welfare, researchers have started to explore the merits of sensory stimulation (i.e. stimulation designed to trigger one or more of an animal's senses) as a potential method of environmental enrichment for captive animals. This paper reviews the research in this area, focusing specifically on auditory, olfactory and visual methods of sensory stimulation. Studies exploring the efficacy of each type of stimulation as an enrichment tool are described, where appropriate, making a distinction between those that occur in the animal's natural habitat, and those that do not. Overall, it is concluded that sensory stimulation harbours enrichment potential for some animals housed in institutional settings, although the specific merits gained from these enrichments are likely to depend upon a wide variety of factors including, for example, species, sex, age and housing conditions. Programmes of sensory enrichment that target the dominant sense for the species under scrutiny, using harmless, non-stressful stimuli, are likely to result in the greatest benefits for animal welfare. Stimuli specific to a species’ natural habitat should not always be considered meaningful, or advantageous, to an animal's welfare; in some cases stimuli that do not occur naturally in the wild (e.g. classical music) may offer more in the way of welfare advantages. Shortcomings in the research, and factors to consider when implementing enrichment of this nature, are discussed throughout.