Zoos and Stress [Research]

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  1. Why should you care?

When you go to visit a zoo or some type of wildlife enclosure – what are your intentions? Are you there to simply view the many species from afar and admire their beauty? Or perhaps are you there to gain a better understanding of how a certain species behaves in a wild setting? Whatever the reason, it is important that you look deeper into the eyes of the species that you are viewing.

Despite how natural to the human eye wildlife enclosures may appear – there are often various unnatural stimuli animals in captivity must combat with. These stimuli initiate various stress induced responses within the animals depending on the species and the type of enclosures.

And say for example, you are there to get an idea of what an animal looks like in the wild… Have you ever considered what that species’ natural habitat might actually be like? And how does this enclosure you are viewing compare with an otherwise wild setting? Have you considered the ecosystem services this animal relies on that it might not be getting – despite best efforts by zoo keepers?

Because when it comes down to it, animals in captivity are known to portray abnormal behaviors that they would not otherwise display in the true wild. These behaviors are known as stereotypic behaviors or stress induced responses that in some way help the animal handle the effects of captivity. So, as you are watching these beautiful creatures within their enclosures, you might not always be getting a true representation of what their normal behavior is like as they attempt to cope with these well-known and documented stresses.

This is not to say that all zoos and other educationally focused organizations relying on animals within enclosures should be completely abolished (while there are some that absolutely should). However, what we do need is to ensure to our absolute best abilities that our motives for keeping animals within captivity are pure, are unselfish, and that we are continually working towards the ultimate international conservation efforts of the species.

Additionally, there are certain animals that for various reasons cannot be released back into the wild. For example, some may have been born and raised in captivity for too long, inhibiting their ability to provide for themselves in their natural environments. Others may have injuries that require rehabilitation. Some may be so rare or endangered that they require more direct protection in the form of captivity to allow their populations to grow. Together, these and other circumstances aimed at protection and education demand that we continually study how various species act within their environment and why.

So, if we are to continue housing animals in captivity (whether temporarily or permanently), the enclosures must be unique to each species, stress reducing in design, and focus on the well-being of the animal. The animal should be first and foremost the entity of concern. Because if we are truly seeking to educate the public about how a species looks and acts outside of defined boundaries, we must continually ensure that we are monitoring and providing the best possible living situation for animals within them.

2. Why was this study carried out? 

Researchers gathered information regarding the causes of stress and stereotypic behavior from animals in captivity in order to understand how we can better mitigate for these actions within zoo settings. Realizing that different species require unique forms of care within captivity, the researchers generalized stress causing agents into five categories; Sound, light conditions, odors, temperature, and substrate. 

3. How was the study carried out?

There was no actual experiment that occurred in the study – rather the researchers compiled mounting evidence towards several reasons for why stress induced behaviors can occur. The study used evidence from existing animals in enclosures to inform readers and widen perspectives of areas to consider when ensuring the well-being of animals in captivity. While the study does not offer complete remedies for stereotypic behaviors in captivity, it does suggest areas to consider before creating enclosures and how to identify with certain behaviors in captive animals.

4. What were the results of the study?

Sound: In captivity, high frequencies of different sounds are often created that animals in the wild are not otherwise faced with. Whether this is through manual construction in surrounding areas, the calls of other species, or sound waves too high or low for humans to hear, unnatural sounds have been proven to cause stress in captive animals. Visitors to enclosures conversing with each other, urban transportation, water features, and cage cleaning can also negatively effect wild animals in enclosures.

In the wild, surrounding sound levels vary depending on habitat. Rain forests have the highest recorded sound levels of all natural environments followed by riverine and savannah habitats. However, zoos and other enclosures have much higher sound levels than even the busiest of rain forests. For example, in rain forests, much of the sound comes from the wind, rustling leaves, and other animal species. In riverine habitats, the sound comes from birds, insects, and the rustling of plants. Savannah habitats are largely quiet with most noise coming from the wind. These natural sounds contrast sharply with the human-induced sounds that often infiltrate the surrounding areas of wildlife enclosures.

These sounds can impact many species, particularly those that are often considered prey species in the wild. Prey species are more sensitive to sounds in the wild in order to protect themselves and/or their offspring. Additionally, stress inducing sounds can cause pregnant animals to give birth to offspring that exhibit abnormal social behaviors, changes in their ability to hear, impaired learning, and unusual levels of various hormones.

Light Conditions: Often, lighting in captive environments is designed to benefit human caretakers as well as visitors. This can be problematic since animals in the wild do not function in the same way and at the same time as humans. Additionally, many animals are sensitive to different wavelengths of light that humans may not be. This can be stressful to animals whose natural circadian rhythms are impacted by varying (or predictable) light patterns around their enclosures. Lights emitting high frequency wavelengths have been shown to cause increased aggression in different species leading to abnormal behaviors.

Many species of reptiles and birds among others require certain UV wavelengths to be able to see correctly. These UV wavelengths also can help them determine when is the best time of day to look for food or seek safety. However, in captivity they are not always provided the needed light levels to do so, causing stress induced behaviors. These are just a few of the ways different light patterns and levels can negatively impact animals in captivity.

Odors: Almost all animals are microosmatic. This means that they rely on odors in their environment to help them make various decisions and learn about their surroundings. However, in captivity there are a multitude of unnatural smells that animals are presented with every day. Whether it is by human visitors or surrounding animal enclosures, unnatural smells can cause animals to feel disoriented as they seek to adapt to their captive environment. Even the smell of urine emitted by another stressed out animal nearby has been shown to increase stress in certain species.

Certain animals also depend on the smells emitted through the chemicals of others to determine when is the correct time to mate, hibernate, and interact overall. However, when these smells are disrupted through changes in a human constructed environments or due to increased levels of stress in surrounding animals, stereotypic behaviors can occur.

Routine cage cleaning of certain species can also be stressful. As smells that would otherwise be maintained over time in a natural environment are removed at the discretion of human keepers, many species can feel disoriented. Species using territorial markings must adapt to being an enclosure where their scent is not always present which in the wild can suggest they are within unknown territory.

Temperature: In the wild, most animals have the option to migrate, seek cover, or move from areas that they find to be thermally uncomfortable. In captivity, animals are limited to their range of motion which can cause them to feel incapable of adjusting to new temperatures. This lack of ability to feel in control of a situation can cause stereotypic behaviors in captive animals. Additionally, animals at different ages and maturity levels may require variations in temperature. Seasonal changes can also be different depending on where a captive animals home range is and where it is being kept.

Certain animals have been found to become more aggressive in warmer temperatures that they are not accustomed to. Captive baboons have even been documented as staying closer to their mothers in cooler temperatures for longer periods of time, preventing their proper maturation and growth. Overall, many species behaviors are directly related to temperature. This variable must be considered when creating and maintaing animal enclosures depending on the species in captivity.

Substrate: One way that many animals can cope with changing temperatures in their environment is through thermoregulation. This can be influenced by the type of ground their enclosures are placed on. For example, concrete, tile, wood chips, soil, grass, wood, and rubber all vary in their ability to keep and release heat/cold from the environment. Additionally, the color of flooring in enclosures can impact their ability to gain or lose heat. Darker colors absorb heat more quickly while lighter reflect. Even the walls or ceilings of enclosures can influence how temperature is created and maintained in captivity.

This is problematic if a species’ thermal preferences are not properly understood – even if we provide them with the proper shade or open areas to respond to changing temperatures. Because even if the environment they are placed in seemingly houses the right temperatures, the substrates around the enclosure can cause unforeseen changes in heat or cold – initiating abnormal stress responses from the animals in captivity.

For example, concrete and wet soil gain and lose heat more quickly than turf does. However, in many captive settings substrates are chosen based on monetary expenses, ease of cleaning, and availability. Substrates that vary significantly from those in a wild setting for a species are capable of causing stress, even in the most seemingly natural of captive settings.

Because substrate temperature impacts the temperature of the air just above or surronding, consideration must be given to animals that live more closely to these areas. For example, a recording of the temperature in an enclosure might not accurately reflect the temperature at a range more near to the enclosure’s ground or walls.

Additionally, cage height can influence how animals perceive their environment. For example, certain species may consider eye contact a threat. For this reason, building enclosures for these species that allow them to look past visitors or avoid direct perception by humans or other animals can be beneficial. Others might use higher areas within an enclosure as a safe place to retreat when faced with a stressful situation in captivity. For these and many other reasons, a large amount of consideration must go into enclosure design for each species.

Overall, an animal’s specific species behavior, dependancies on ecosystem services, and natural instincts must all be well understood before placing into captivity. Otherwise, the well-being of the enclosed animal is at risk as well as the perceptions of the humans visiting the enclosures. This requires a large amount of research, observation, and consideration of the many aspects of captivity that the human eye and sensory abilities might not immediately realize.

We must learn about the animal first and all its intricacies – before we attempt to teach ourselves and others of them.

5. Want to know more details?

What do you think? Any questions? Please send them my way in the comment box below and I will do my best to find out the answers for you or to just respond back.

Also, check out the original article, Sources of Stress in Captivity, if you would like to view a more detailed version of the information summarized in sections 2-4 above.

Authors: Kathleen Morgan and Chris Tromborg

Published: July 2006 by Applied Animal Behavior Science

One response to “Zoos and Stress [Research]”

  1. […] ensure that the habitats they provide for each species is as natural and enriching as possible. When creating such enclosures issues such as lighting, sound, odors, temperature, and substrate mus… These enclosure characteristics will be unique to each species and thus, will firstly require a […]


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