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Last updated January 1, 2014

Miscellaneous Factors Affecting Health and Welfare

Excerpt from Chapter 11 in Health and Welfare of Captive Reptiles, C Warwick, FL Frye, and JB Murphy, eds., Chapman & Hall, London, 1998.

Phillip C. Arena and Clifford Warwick


11.3.2 Thermal Burns
An example of apparent but almost certainly misunderstood physical insensitivity and poor thermal environments concerns thermal burns, which occur when captive reptiles come into direct contact with heat sources while attempting to raise their body temperature to preferred levels. The general problem may be exacerbated somewhat by ambient temperatures that are too low and which result in animals being forced to raise their body temperature through extreme proximity to heat sources (J.B. Murphy, pers. comm.). Damage from thermal burns ranges from minor lesions and scarring of the skin to extensive injury such as fusion of the eyelids or burns that extend deep into the body tissues (Frye, 1991a). These injuries may lead to permanent defacement, disability or death. In addition, although light and heat sources are available which approximate the range of spectra present in solar radiation, the mere proximity of the source to the reptile may be damaging to ocular tissue, particularly in the case of fossorial, crepuscular and nocturnal species (which are likely to be thigmotherms - see Chapter 6).

The point of particular interest here is that the individual may appear to be oblivious to gross trauma during the period of damaging injury, and in fact insensitive to pain. One current view is that these burns arise after an animal has rested against an inactive heat source, which is then activated and beats up rapidly, causing tissue and presumably local neural damage (Frye, 1991a). Anecdotal accounts suggest that reptiles also settle on already active heat sources and then suffer burns. We propose that a major reason for this behaviour is twofold. First, a large reptile may not be able to attain an optimal body temperature from a small intense heat source such as a lamp. Second, thermal provisions in captivity fail to simulate adequately the thermal diversity of the natural environment.

In nature the thermal requirements of, for example, a heliotherm are satisfied by a radiant solar source which bathes the entire animal with heat. However, the efficiency with which a body absorbs warmth depends on not only its own properties but also other factors including the intensity of the heat source, the position of the body with respect to the heat source and the proximity and properties of other reflective surfaces (Geiger, 1959). Thus a thermally receptive body is subject to thermal inputs of a multidimensional and heterogeneous nature. Different regions of a reptile's body have different absorbency spectra and thus different heating rates (Heatwole and Taylor, 1987). In captivity, often the only source of heat available is one or two small and usually intense heat lamps. In order to raise their body temperature, reptiles move toward a heat source and bask. Especially where large reptile species and individuals are involved, with associated slower blood circulation (Coulson and Coulson, 1986) and thus heat dispersal, these animals must attempt to raise the temperature of the entire body using primarily diminutive heat sources. Thermal absorption is attempted while continually losing warmth from body surfaces that are not exposed to the heat source and which may, indeed, be in contact with 'cold' surfaces that conduct heat away from animals.

Compensatory behaviour may include moving closer to the heat source where upon the peripheral nerve endings are damaged and desensitized. Once this occurs, the reptile moves closer still and eventually contacts the heat source in an attempt to raise its body temperature to an optimal level, a point it may never achieve. Thus an unnatural thermal environment and related 'biological confusion' may result in thermal burns. Clearly, more data are needed to clarify the reasons behind this aberrant behaviour, especially in consideration of body size and associated heating requirements of reptiles. If this hypothesis were supported, heliotherms of a small body size in particular, would be less likely to suffer thermal burns because a heat lamp is, to them, a relatively expansive source that may more appropriately 'saturate' their bodies entirely.

Related considerations include the fact that large lizards are more reflective of solar radiation than smaller individuals (Norris, 1967) and that they heat and cool at a slower rate as a result of a low ratio of surface area to volume. Snakes, by the very nature of their morphology, may be compromised by inadequate thermal provisions.


11.3.3 Light and Photo-Invasive Environments
Because photoperiods are integral cyclic influences on the biological responses of an animal, these to an extent control various physiological and behavioural parameters. In many captive situations, reptiles are provided with a single combined source of heat and light. These may be operated manually or automatically set to particular light and thermal. Periods which may not correspond with natural conditions. Unfortunately, in the captive environment, photoperiods are often based around convenience for keepers rather than natural patterns for the captives. Apart from obvious physiological and behavioural disruptions brought about by unnatural photo and thermal periods, it is also suggested that incompatible periods, and especially prolonged exposures to light, are probably a significant stressor in captive reptiles (Warwick, unpub.). Photo-invasive environments may also be highly disruptive on rest and sleep quality. Consequently, it may be imperative that animals are always provided with suitable hiding places where individuals may avoid light at any time, as well as ensuring 'normal' periods of light and dark.

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