April - Chicago Herpetological Society

scientific literature supporting points (b) and (c), we will not
dwell on these matters, but we will concentrate on the first
point. It is probable that numerous ophidian species identify
their keepers, but to our knowledge this has not yet been verified
in an experiment specifically designed to demonstrate
same. Hence, we have mainly anecdotes, some quite convincing,
as are those provided by the Barkers for all three points.
Advancing beyond the anecdotal level is nevertheless required
in order to put the issue on a scientific footing. Years ago an
undergraduate at our institution was hunting during Spring
semester for an independent study (3 credit) project so as to
permit graduation at the end of the term, and we pointed him in
the direction of point (a). The idea was to place into several
snake cages a small item of clothing worn by a person. Control
snakes would get identical items that were clean (unworn and
non-odoriferous). After living with these materials for a week
or two, all cages would be cleaned, an operation that always
elicits tongue flicking and cage exploration. All snakes would
be placed into their respective clean cages along with the items
of clothing that had previously been present. The hypothesis
was that the now-familiar human chemical cues would exert a
calming influence, reducing the dither of exploration, whereas
the control snakes would exhibit no such effect. This notion
was based on the fact that familiar chemical cues of other sorts
had significant calming influences under identical conditions.
To add a convincing touch, some snakes in the experimental
and control conditions would receive clothing worn by an
unfamiliar human, and these items should exert no calming
effect. By the end of the semester the study was only partly
complete, but with encouraging results. Alas, neither the student
in question nor any other elected to finish this project, so
we did not end up with a publishable demonstration. We mention
the project here as a promising experimental design and,
hence, as a candidate for interested persons (perhaps the Barkers)
to pursue.
6.) “ . . . the ability of a snake to flick its tongue to one side or
the other creates a sense of olfaction that is directional.” (p. 24)
This may be only the beginning of a much larger story. Consider
a snake tongue flicking along, say, the right margin of a
trail. Sometimes the tongue or one of its tines will touch the
trail, sometimes both tines will be off the trail. In the first case
relevant chemical cues will be transported to the vomeronasal
organs (VNO), in the second case no such cues will be brought
to the VNO. Not only can this state of affairs give rise to
directionality, it can also produce a sensory contrast effect,
enhancing the detectability of the border. Contrast might be
especially sharp when one tine touches a trail and the other is
off the trail. Augmented perceptions arising from such contrast
effects are well known in the visual and tactile systems of a few
organisms commonly kept in laboratories, and we understand
the neural mechanisms that mediate these phenomena. It is
possible that similar mechanisms exist in the nasal and vomeronasal
systems, as these mechanisms would contribute to more
effective trail detection and following than would otherwise
occur. To our knowledge, no one has yet tested this hypothesis
either at the behavior or neural levels.
7.) “The ability of snakes to interpret and understand certain
sounds and to respond with consistent predatory or defensive
behavior suggests that auditory stimuli may play a larger role in
the behavior of snakes than was previously realized (Young,
2003).” (p. 25) Clearly we are standing at the very threshold of a
new frontier of ophidian research, and numerous hypotheses can
be externalized from this quotation. One that the Barkers developed
several paragraphs later was......”the answer to a commonly
asked question about ball pythons is, ‘Yes, your snake can hear
you when you talk to it.’” (p.25) A possible functional significance
of this capacity if it exists might be approached with a
variation of the experiment proposed in point 5 above.
8.) “One example of the sensitivity to touch that has always
impressed us is a ball python’s apparent ability to distinguish
between being touched by an inanimate object, such as something
made from metal or glass, and being touched by something
living.” (p. 25) This passage made us think about bull snakes
pressing mice against cage walls with rear sections of their
bodies while the head was busy ingesting the first mouse. At the
same time, the bull snakes ignore the snake hook, the tongs, or
cage furniture. Separating the effects of thermal, chemical and
tactile cues in these examples would provide some understanding
of how the snakes manage such discriminations.
9.) “Most snakes have radiant-heat sensing thermoreceptors in
their skin. These are associated with the occasional need to bask
in warm places to mediate their body temperatures.” (p. 25) See
Barker (2008) for an interesting follow-up to this statement, with
surprising results. Although there is no doubt about the existence
of shuttling thermoregulation in some herps, we may have
over-generalized this phenomenon.
10.) “De Cock Buning (1983) estimated that at 77 degrees
Fahrenheit (25 degrees Celsius), a python could detect the heat
signature of a medium-sized rat at 19 inches (48 cm). Molenaar
(1992) estimates that a python can detect a rodent that is 18
degrees F (10 degrees C) warmer than the environment at a
distance of 13 inches (28.8 cm).” (p. 26) While we know a great
deal about the neurophysiology of infrared detection and processing,
precise predictions such as these have not yet been
tested at the behavioral level. These straightforward hypotheses
can give rise to a wonderful program of research.
11.) “It’s possible to bitten by an otherwise totally tame and
inoffensive ball python if one inadvertently triggers this behavior
by, say, putting a warm hand in front of the door of a hide box
that is housing a sleeping ball python.” (p. 27) Yep, and it is
equally possible to be struck by a rattlesnake when offering a
room-temperature euthanized mouse suspended from tongs held
by a warm hand. Experimental analyses of these husbandry
“rules of thumb” would be useful not only as confirmation of our
suspicions but also as demonstrations of the fact that infrared
cues can over-ride visual ones, at least under some conditions.
12.) “The two types of cones in the ball python eye occur at
densities of 45,000 cones per square mm in the retina. . . . The
visual pigments found in one of the cone types are very sensitive
to ultraviolet light. . . . It is known that some animals, including
snakes and lizards, leave scent trails with ultraviolet activities;
some of the chemicals either absorb or reflect ultraviolet light
(Alberts, 1998). . . . Sillman et al. (1997) demonstrated that
garter snakes (Thamnophis sirtalis) have visual pigments and
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