Adaptive traits — does ‘can’ imply ‘should’?

Herps have many interesting adaptive traits.  Consider the heat sensing facial pits of some pythons, such as Python regius, the Royal python (yes, the British common name is the better one).  Royal pythons sense the body heat of the warm blooded prey they hunt, and use that sense in order to strike more accurately and thus hunt more successfully.  It doesn’t work on cool dead prey, of course, and isn’t at all necessary for striking warm dead prey.  But Royal pythons are clearly adapted for hunting live rodents and birds.

Another adaptive trait is the ability to manufacture Vitamin D from ultraviolet light, specifically UVB (though UVA plays a huge role in the process, which is a tangent best taken up in another post).  Most herps that have been studied have been found to have this ability, at least to some degree (except, coincidentally, Royal pythons).  It isn’t necessary for a herp to make their own Vitamin D if they can ingest and metabolize Vitamin D and their diet contains it (whether naturally as in rodents or supplemented by the keeper as with insectivores), but many herps can use both oral and UVB-derived Vitamin D.  It seems that many keepers are being convinced to provide UVB for nearly all herps, even those that use oral Vitamin D perfectly well.

Of course, UVB isn’t all good for any animal; it can cause cancer and eye disease, and induces anorexia in captive herps if misused.  It is also expensive (fixtures, a meter, periodic lamp replacement, and electricity)  And the same sorts of things can be said about live prey for Royal pythons — feeding live rodents (and I suppose live birds, though I have not heard of such a practice) carries a serious risk of injury to the python (and possibly suffering of the rodent), and they’re more expensive to buy (and maintain, when the snake refuses a meal).  Current hobby practices seem mostly to discourage feeding live rodents, except in those cases where that’s literally the only prey that a particular snake — or in some cases, a particular species — will accept.

These of course are only two of innumerable examples. Many herps have adaptive traits that help them to swim, to brumate; some to aestivate and even to glide.  The skin of some is adapted to slough off when grasped by a predator.  All have adaptive traits that maximize their reproductive output.

Because a herp has an adaptive trait, the role of which can be provided by other options in captivity or skipped entirely without harm, does that automatically mean that we keepers should promote the herp’s use of that trait?  Why are practices around UVB and live feeding so different in spite of having similar roles in the life of a herp?  


David W. Gardiner, Frances M. Baines, Karamjeet Pandher "Photodermatitis and Photokeratoconjunctivitis in a Ball Python (Python regius) and a Blue-Tongue Skink (Tiliqua spp.)," Journal of Zoo and Wildlife Medicine, 40(4), 757-766, (1 December 2009)

Hedley J, Eatwell K. The effects of UV light on calcium metabolism in ball pythons (Python regius). Vet Rec. 2013 Oct 12;173(14):345.