Play learning and plasticity

Although play behavior occurs in a few species at least under captive conditions, most species do not exhibit this phenomenon. Play observed in reptiles has not been a social phenomenon. It has involved the deployment of foraging, feeding, or other behaviors in unusual, nonfunctional contexts, sometimes aimed at inanimate objects, sometimes at humans. The players have been adults, and their playful activities have been idiosyncratic rather than common among con-specifics.

Exhibition of play behavior as a social phenomenon is a major difference between reptiles and mammals, with birds positioned in between. The usual explanation is that most reptiles have been strongly selected for precocity. Neonates are miniature versions of adults and must function effectively as predators, as avoiders of predators, and as competitors. They have no leisure to acquire behavioral skills during playful interactions with peers or by observing parents.

Even the most precocial (capable of independent activity from birth) birds and mammals have opportunities to learn,

A cornsnake (Elaphe guttata guttata) kills a rat by constriction. (Photo by Animals Animals ┬ęCarson Baldwin, Jr. Photo reproduced by permission.)

although this process may be accelerated, as it is in filial imprinting in precocial fowl and analogous social phenomena in some precocial mammals. There are important ontogenetic effects of early social stimulation in these birds and mammals. In the more altricial (immature or helpless at birth) species, similar effects occur over a broader span of time, play being an important context for social learning. In reptiles, by contrast, such effects are less common. The usual observation is that neonates are competent at biologically significant tasks the first time they encounter the task.

This does not mean that learning is unimportant in reptiles, only that it is a less conspicuous aspect of reptile ontogeny than is the case for birds and mammals. For example, several species of turtles develop strong preferences for the foods encountered after hatching. The turtles are capable of accepting many different types of prey, but the types available at the time the turtles hatch becomes favored prey as a consequence of an imprinting-like phenomenon that occurs during early feeding experiences. Because piscine prey species can fluctuate in abundance, even replacing each other owing to normal ecological events, hatchling turtles apparently are better off without strong, innate preferences but with the capacity to form preferences after sampling foods that happen to be present in the posthatch habitat. A strong innate preference for a prey type that happens not to be available could have disastrous consequences, whereas experientially induced preferences would simply adjust the predators to prey currently in the food web.

Only when the composition of the food web is predictable or reliable does it make sense for neonates to have innate preferences. This phenomenon is well known in garter snakes.

Adder snake sidewinding in the Namib Desert. (Photo by David Hughes. Bruce Coleman, Inc. Reproduced by permission.)

Neonates exhibit strong preferences, on the basis of chemical cues, for prey normally present in their habitats. Even here two points are of interest. First, results of experiments have shown that neonates typically exhibit several preferences; they do not prefer only a single prey species. If one type of preferred prey is not present, another will probably be available. Second, although they have strong innate preferences, neonates are capable of acquiring new preferences on the basis of early feeding experience. If none of the preferred prey are available, hungry neonates are flexible enough to adjust to new foods.

The flexibility of adult snakes and other adult reptiles has not been studied experimentally, but the husbandry experience of zoo professionals and that of many hobbyists indicates that some species readily adjust to captivity and to the foods normally provided there, whereas other species make this transition only with great difficulty. Most rodent-eating snakes typically do well in captivity, even when captured as adults. The same is true of fish-eating species, especially if rodents are facultatively present in the natural diet, such that the snakes can be switched to rodent prey in captivity. Snakes with highly specialized diets are typically difficult to keep in captivity, but this problem usually is associated with the fact that the keeper has difficulty obtaining the necessary prey in sufficient quantity.

Even notoriously difficult species can be kept in captivity, if specialized habitat factors and required foods can be provided. This judgment is based far less on scientific data than on accumulated experience of gifted, dedicated keepers. Our experience with the viper boas (genus Candoia) is consistent with this point of view. Species that take rodents adjust well to captivity, whereas species that take lizards are quite difficult to keep, unless appropriate lizard prey are available. When such prey can be offered, the snakes accept them and remain in good flesh. Lizard prey, however, are not regularly obtainable, and because the lizard-specializing snakes do not readily switch to rodents, the snakes generally become thin and vulnerable to infections that occur as a secondary effect of nutritional compromise. This outcome is a shame because lizard-eating viper boas have pleasant personalities, being tolerant of handling without offering to bite. They could be easily maintained in captivity if the food problem could be solved. Commercially produced rodent prey are widely available in the United States. The rodents are generally free of infection and relatively free of parasites, especially dangerous ones. Wild-caught lizards are sometimes infested with microbiotic and macrobiotic organisms that can readily colonize snakes with disastrous consequences. This is another reason that rodent-feeding snakes have an advantage in captivity.

Although rodent-feeding snakes usually are easy to keep in captivity, there are exceptions. One of the most famous is the eastern diamondback rattlesnake (Crotalus adamanteus). Neonates born in captivity do fairly well, but wild-caught adults rarely thrive, even under the best husbandry conditions. This fact is all the more interesting because western diamondbacks are no less aggressive and no less likely to remain aggressive in captivity, yet they generally do reasonably well, accepting prey readily and breeding with alacrity when given the opportunity under appropriate thermal conditions. Neonatal western diamondbacks born in captivity usually are calmer than wild-caught adults, but the latter usually manage to do well in captivity even with their notorious dispositions. Why wild-caught adult eastern diamondbacks and western diamondbacks differ in their tolerance of captivity remains a mystery that probably involves a difference in behavioral and emotional plasticity. Unraveling this mystery will not only shed light on the dynamics of these species but also contribute to the ability to manage many other species in captivity. Problems similar to those among wild-caught eastern diamondback rattlesnakes have been reported in many other species. Providing appropriate habitat may be part of the solution. Many keepers report success with defensive individuals if hiding places are provided. To our knowledge, experimental tests have not been performed, and we see here an excellent example of the interface between behavioral research and the development of good husbandry techniques.

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