Rodents as a Food Source. Feeding Patterns

Neonatal mice and neonatal rats (pinkies) can be offered on occasion to aquatic and terrestrial amphibians, however one study reported that the levels of vitamin A in these domestic rodents are high (Douglas et ah, 1994). If this study is valid, hypervitaminosis A could contribute to the development of metabolic bone disease if mice or rats are used on a regular basis without vitamin D₃ supplementation. (See also Section 7.1, Metabolic Bone Disease, and Toxicological Etiologies—Hypervitaminosis A in Section 27.2.1, Musculoskeletal System.) Given a whole body content of about 27 iu vitamin A/g body weight for rat pinkies (Douglas et al., 1994), a supplement of at least 2.7 iu vitamin D₃/g body weight may be needed to offset the high levels of vitamin A in rat pinkies. However, this supplementation rate has yet to be tested for longterm safety and efficacy in amphibians and may well result in toxicides from the fat-soluble vitamins. To avoid this risk the feeding of rodents to amphibians should be minimized.

Feeding Patterns. It is important to offer food items at a time that is cued to the activity pattern of the species as well as the individual specimen. Establishment of a regular photoperiod in an enclosure allows the inhabitants to develop appropriate activity patterns. Avoid sudden shifts in the photoperiod as these may disrupt the amphibian’s biorhythms and alter its feeding behavior. Diurnally active amphibians, such as den- drobatid frogs, should be offered food in the morning and early afternoon, while nocturnally active amphibians will feed most readily if offered food in the early evening.

The lighting of an enclosure may influence an amphibian’s activity pattern (Jaeger & Hailman, 1981); thus the illumination should be appropriate to the species. Some nocturnally active snakes show a cycle in foraging activity that corresponds to the phase of the moon and associated illumination intensity (Personal communication, P. Andreadis, 1997), thus a regular fluctuation of the nighttime illumination may prove beneficial to some amphibians.

The radiation wavelength of the light source used in an enclosure may also influence the behavior of animals (White et ah, 1994), and the light source should be chosen to meet the known needs of the species. Species that are diurnally active but live on the forest floor may not be accustomed to intense lighting and may hide rather than eat if kept under inappropriately high light levels, possibly giving the caretaker the erroneous impression that the species is crepuscular or nocturnal. Erratic behavior is often noted when the light levels or photoperiod is inappropriate.

If food items are offered at inappropriate times (e.g., first thing in the morning for a nocturnally active species), the vitamin and mineral supplementation may not be effective, as the amount dusted onto the prey may be groomed or wiped off, and the contents of the gut may be excreted.

If an amphibian is not hungry, the uneaten prey may in turn consume the amphibian. Crickets are notorious for eating small amphibians or eating wounds on larger amphibians. An amphibian may be hungry and willing to eat, but if too many prey items are present an amphibian may be reluctant to feed due to tactile stimulation of prey items crawling on its body.

The amount of food offered and frequency of feeding depends on the energy budget of the species in question. Small, actively foraging amphibians may need to be fed twice a day to maintain good body weight, whereas large ambush predators may gain excess weight if fed to satiation more often than once or twice a month.

Environmental cues such as temperature and humidity can influence feeding behavior. Body temperatures far below or above the preferred body temperature for a species can make an amphibian reluctant to feed, as can a decrease in total body water such as may be brought about by inappropriately low humidity within an enclosure. Poor water quality caused by an elevated pH or low levels of dissolved oxygen can put an amphibian off feed, and should be evaluated whenever there is a problem feeder.