Outdoor Enclosures

Primary Barriers

The barrier between rhinos and the viewing public is a critical element in the design of the outdoor exhibit. This primary barrier should allow visitors a clear view of the animals from a safe location. Many types of primary barriers are available, the most common of which are walls, fencing, dry moats and water moats. One consideration in choosing fence type should be the size of the enclosure. For example, smaller exhibits should be constructed with barriers that provide as much visual exposure as possible. Moats, both dry and water, are less desirable for breeding groups because of the potential for accidents. 

 

Recommended materials for primary fencing include solid concrete or rock walls, horizontal pipe or cable spaced 25 to 30 cm (10-12 in) apart, and vertical pipe or posts spaced 25 to 30 cm (10-12 in) apart. Cable should be used only for horizontal fences. The size of the exhibit to be fenced will determine the strength and type of fencing material used, as each type has both advantages and disadvantages. Concrete surfaces and bare steel cable create surfaces that may encourage rhinos to horn-rub excessively, causing abnormal horn wear. If necessary, surfaces should be covered with a non-abrasive material; one solution is to insert steel cable through plastic pipe, or concrete surfaces can be covered with non-toxic wood. If poles are used, each should be approximately 30 cm (12 in) in diameter and set in concrete with approximately 1.8 m (6 ft) underground. Poles should be spaced as closely together as possible to prevent rhinos from getting their horns through and uprooting the fence. Creosote-treated poles, which are dangerous to rhinos, should not be used. Rocks or a rock apron can be utilized to protect the poles or other objects in the exhibit from damage. A rock apron should extend 1.8 m (6 ft) from the leading edge of the object to offer adequate protection. If small rocks are used, they should be several layers thick; otherwise, a single layer of very large rocks is probably adequate.

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Fencing

Because any of the rhino species may climb, a primary barrier should be a minimum of 1.5 m (5 ft) high and non-climbable. In small enclosures, particular attention should be given to the climbing ability of rhinos and to the need for separating aggressive animals. A secondary barrier or a taller primary barrier may serve to counter these problems. It is important to consider fence spacing and keeper access/exit in the event of an emergency as well.

It is important to note that vertical posts spaced wider than 12in apart may allow smaller rhinos to pass through. At one facility, a black rhino that was just under two years old was able to force its way between bollards that were spaced 21.5 inches apart, which can pose the hazard of a rhino getting stuck. In this instance it appeared that spacing of 18 in would have been sufficient to keep the rhino from pushing through.

 

Square vs. round bollards/posts: There are pros and cons to each shape of posts. Square posts seem to be more difficult for rhinos to push through. This then becomes a drawback should a rhino get stuck in between; it is more difficult for them to squeeze back out. Though rhinos can still get stuck between round posts because they are easier for rhinos to push through, reduced resistance and may allow for them to push themselves back out from being stuck better than square bollards. (Moeller, 2023) Chain-link or stay-tight fence has been used as a barrier to keep small-sized rhinos from trying to push through vertical bollards spaced too widely, however the rhinos can damage the fence making it a non-viable and unsafe solution. Using smaller wood posts to wrap around vertical posts is a simple and effective way of increasing the post diameter and reducing the spacing of vertical posts. These posts can be strung together with chain and secured with shackles.

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Dry Moat

The use of a dry moat requires one vertical wall, which should be a minimum of 1.5 m (5 ft) high, located on the public side. The second wall should be sloped at a maximum of 30° so that the animals can climb out. This gradual decline of the exhibit substrate down to a solid wall can be used to create a moat effect, but ditch moats with two vertical walls are considered dangerous to rhinos and are not recommended. The floor space in the moat should be a minimum of 1.5 m (5 ft) across to prevent rhinos from being trapped, and surface substrate for the moat should provide stable footing (recommended materials include dirt, gravel, sand, etc.).

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Water Moat

Water should not be utilized as a primary barrier as it carries the risk of drowning or injury, especially for calves.

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Secondary Barriers

Though not critical to the design of outdoor enclosures, secondary barriers may protect exhibit features or lessen stress on primary barriers. Recommended types are butt rails, vertical poles and electrically charged, or “hot” wire. Plantings can also serve as a secondary barrier when used to create a visual screen. For example, plantings that extend above a low wall can give the appearance of a bigger wall [although the primary barrier height minimum of 1.5 m (5 ft) still applies]. Electric fencing can deter animals from destroying plantings, trees and other secondary barriers. Rock aprons may also be used around trees and fence lines as secondary barriers.

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Gates

Enclosure gates can be the weakest points of the exhibit, therefore adequate hinge and lock strengths are very important. Interior doors are usually constructed of heavy-gauge steel or pipe that is hinged or sliding. Sliding gates are optimal, as they have the ability for partial opening, and should be a minimum of 1.8 m (6 ft) wide and 2 m (6 ft 8 in) high. If the gate uses a track, care should be taken in the construction of the track to avoid injuring the feet of the animals as they run through gates during introductions. Exterior building doors may be made of steel or wood reinforced with steel, with the lower part covered by a steel plate to minimize damage. Gates should be constructed to allow keepers to open and close them without entering rhino space. Also, where appropriate, vehicle access to an enclosure should be provided.

There are a variety of options available to operate gates. The simplest systems are manually operated, either push-pull or cable driven. Rhino-size doors can be heavy and difficult to move. Mechanical systems can make this easier, using electric motors or hydraulic or pneumatic pressure to move the doors. These systems require some form of back-up system in case of a mechanical

or power failure. Mechanical systems can generate significant forces that can injure or even kill an animal. Safety measures have to be incorporated into the design of the gate operating system to prevent accidents.

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Substrate

The outdoor enclosure should have a well-drained surface that provides adequate footing for rhinos. Black rhinos should be maintained on grass if the space is available, but limestone is adequate. Rhinos should be carefully observed upon introduction to a new substrate, as excessive ingestion of the substrate from feeding on the ground has caused impaction in other hind-gut digesters,

​Modifications to enclosure may be required if problems arise and may require creative thinking to modify either temporarily or semi-permanently. Chain-link or stay tight fence has been used as a barrier to keep small sized rhinos from trying to push through vertical bollards with too wide of gaps. Though after a certain time the rhinos began to damage the fence and it started to no longer become a viable or safe solution. Using smaller wood posts to wrap around vertical posts is a simple and effective way of increasing the diameter and reducing the spacing of vertical posts, these posts can be strung together with chain and secured with shackles.

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Terrain

Many rhino habitats lack terrain variation. Offering this variety should be considered, when possible, in habitat design but should not come at the expense of guest viewing or animal safety. Variety in terrain offers a more stimulating environment for rhinos to navigate, while also creating opportunities for greater physical exercise and muscle building. (Moeller, 2023)

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Water

Fresh, potable water should be available at all times. Water should be changed daily or supplied by an automatic-fill or continuous-flow device. Regular cleaning and disinfecting should occur at a rate that inhibits the growth of algae and bacteria. Water devices should be substantially constructed to prevent injury, upset, spillage or leakage.

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Mud Wallows

Black rhinos need access to mud wallows for skin health, temperature regulation and behavioral enrichment. The size of mud wallows should be gauged by the number of animals in the exhibit so that ample room is provided for each individual. It should be noted that given a start, rhinos may construct their own mud wallows. Construction of wallows varies by institution and exhibit. Some facilities use a concrete basin or pool filled with substrate, while others simply dig out a section of the enclosure. If a concrete pool is used, it should have the ability to be drained when needed, but care should also be taken to protect the drain line from being filled with substrate. If a wallow is dug on exhibit, it should be situated in an area that will allow adequate drainage away from the wallow. It is also important that a good source of water be nearby to keep the area wet. Wallows are much easier to manage if the enclosure allows access for a skid steer or tractor with front loading bucket.

Mud wallows must be actively managed. If the local soil does not create mud of a satisfying consistency, it can be adjusted with the addition of topsoil, clay or sand. Standing water in an animal area can be a potential USDA compliance issue. The wallow should be monitored for the growth of algae. If the algae cannot be removed by raking or scraping, it may be necessary to fill the area in to allow it to dry completely for several days, and then dug out again. Depending on the local environment, the substrate may need to be changed several times during a year to prevent contamination. Institutions in northern climates may need to fill in the wallow during winter months.

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Visual Barriers

Naturalistic visual and physical barriers (refuges) in outdoor enclosures may help decrease aggression by permitting animals to separate themselves from others during introductions or in a group situation. Barriers should be large and high enough to provide “safe zones” that allow an animal to pass from another’s sight but should not hinder public viewing. Types of visual barriers include deadfall, logs and boulders, as well as trees and natural plantings. Trees and plantings may be protected from rhinos by pipe caging, rock aprons or barrier fencing. If permanent physical structures are not available as barriers, dirt mounds may be used to give individuals additional visual barrier points in the enclosure.

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Shade/Rain Shelter

Access to shade is a necessity as well as a USDA requirement under the Animal Welfare Act. A variety of both natural and constructed options are possible. It is also important that a shade option be adequate as a rain shelter if barn shelter is not always accessible; therefore, trees may not be completely adequate. It is a good idea for wallows to be located in areas that are shaded at least part of the day.

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Additional Furnishings

Additional furnishings for the outdoor exhibit should include scratching posts, which may be particularly effective if placed near mud wallows. Post materials must be non-toxic to rhinos (i.e., non-creosote). Several institutions have buried deadfall or logs upright in concrete sewer culverts, which are routed in place with 0.9 to 1.2 m (3-4 ft) of gravel. This enables managers to remove and replace posts as they deteriorate. Feed should be available at all times in the form of browse, feed stations and mineral salt licks.

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