Terrestrial Fossorial Enclosure

The terrestrial fossorial enclosure is appropriate for terrestrial caecilians, many of the mole salamanders, Ambystoma spp., some of the lungless salamanders (family Plethodontidae), the tomato frogs, Dyscopbus spp., and the spadefoot toads (family Pelobatidae).

The basic design for a terrestrial vivarium is appropriate for fossorial amphibians, although the latter animals need a deep soil base of at least 10 cm (4 in) for burrowing (Figure 5.7). The pool area can be quite small or eliminated altogether, unless the species needs a large pool for breeding.

It is best to use an enclosure that maximizes floor space. The height of the fossorial vivarium needs to be only a little taller than the depth of the soil. A 76 L (20 gal) long aquarium works well for a breeding group of medium sized species, such as the marbled salamander, Ambystoma opacum, while larger species such as the Mexican caecilian, Dermophis mexicanus, should be housed in a 114 L (30 gal) breeder aquarium.

Figure 5.7. Lateral view of fossorial enclosure for amphibians. A. cross-section of board supporting the rim of the tank, tipping it toward the drain. B. false floor assembly (see Figure 5.1 В—D). C. pea gravel layer approximately 2.5-5 cm (1-2”) thick. D. soil at least 10 cm (4 in) deep. E. burrow made by a fossorial amphibian. F. leaf litter. G. clip to secure the lid against escapes. H. live, potted plant with the base of the pot resting on the fiberglass screen. I. standard one-piece screened aquarium/vivarium lid. J. hardwood bark or cork bark. K. moist sheet moss. L. single layer of fiberglass window screening to keep the overlying soil from clogging the gravel layer beneath. M. drain assembly (see Figure 5.1 К—M) (Sandy Barnett)

It is essential that a moisture gradient exists throughout the fossorial enclosure, with one end of the tank having drier soil than the other, and the bottom soil being more moist than the surface soil. This will allow the amphibian to seek out an appropriate microenvironment. The easiest way to set up this environment is to use a long aquarium, and tilt it lengthwise with a brick or board under the high end. Always rest the weight of a glass vivarium on the framed rim and not on the glass itself to prevent cracking of the glass or loosening of the seals. Water is then added only at the lower end of the enclosure. This creates a gradient of wet to dry soil from the lower to the higher end.

It is essential to have well-drained soil and an unclogged drain, so that water does not back up into the burrows. To keep the gravel bed from clogging with dirt, a layer of window screening can be laid between the gravel and the soil layer.

Many fossorial amphibians are quite strong for their size and can easily push open a poorly secured cage lid. It is recommended that the lid have a locking mechanism, or be weighted down with a brick or comparably heavy object.

Fossorial species, by their nature, spend much of their time underground, out of view. One strategy for increasing their display value, while still allowing them to exhibit normal burrowing behavior, is to stack pea gravel in a high mound in the center of the tank and place a moat of deep soil around the perimeter, filling in the space between the gravel mound and the walls of the vivarium. This setup allows the amphibian to construct burrows that are visible in cross section. Black plastic or dark paper should be placed over the wall of the burrow to maintain a dark environment whenever the vivarium is not being observed.

Plenty of ground cover in the form of dead leaves, flat rocks, bark, clumps of sphagnum moss, or sheet moss is recommended so that fossorial amphibians can forage on the surface of the soil but remain under cover. Small sections of thermoplastic (e.g., Plexiglas) may be placed on the surface of the soil, which an amphibian may use for cover when on the surface. Dark-tinted thermoplastic is needed for many salamanders to feel secure, but caecilians have such poor eyesight that clear plastic can be used for these bur-rowers.

PVC pipes with rounded edges can be sunk at an angle in the soil to provide ready-made burrows. A see- through burrow can be made by cutting the pipe lengthwise and placing the open side up against the glass. Many ambystomid salamanders will readily use these structures.

Live plants generally fare poorly with fossorial amphibians; the burrowing activity constantly disrupts the root system. Golden pothos, Epipremnum aureum, and Cordatum philodendron, Philodendron oxycardium, are among the hardy plants that handle such disturbances well. If other plants are going to be used, it is best to keep them in their pots. A layer of gravel can be put in the top of each pot to discourage digging.

Another way to add greenery to a fossorial cage is to use an epiphyte log. Its construction is described by de Vosjoli (1995). Basically, the epiphyte log is a roll of cork or a suitable hardwood branch covered with epiphytes of different sizes and shapes.

The fossorial enclosure can be used to estivate certain amphibians, such as sirens, Siren spp., and spadefoot toads (family Pelobatidae). The soil layer should be deep, in excess of 30 cm (12 in), and should be wetted thoroughly. The enclosure can be left to dry out so that the surface of the soil develops cracks from the dryness. Healthy amphibians of cocoon-forming species will create a nest chamber and estivate through this period of dryness. Moistening the soil again will bring the amphibians out of estivation. After the soil has been moistened a few days, buried terrestrial amphibians can be dug up and allowed to rehydrate in a shallow bath. Aquatic amphibians can be returned to their normal aquatic enclosure.