Thermoregulation
How
a chameleon thermoregulates
Chameleons
are Ectothermic.
This means they use external (ecto) sources of heat to raise their
body temperature to its Preferred Optimum Temperature (P.O.T.).
There are
two main ways to do this.
A Heliothermic
(sun loving) animal gets its heat directly from the suns rays.
A Thigmothermic animal gets its heat by conduction when touching
(thigmo) warm objects. E.g. hot basking rock.
Most reptiles at some stage use both methods. Clearly if basking on
a rock in full sun the animal will be exposed to conducted heat and
direct sun light. This is a very efficient way of warming up quickly.
Chameleons however are only Heliothermic. Their arboreal lifestyle
restricts them to this method. To overcome the lack of heating by
conduction they have developed both behavioral and physiological methods
to make them very efficient Heliotherms.
Simply
moving into the sunlight (basking) to warm up and into the shade to
cool down or maintain body temperature is the most basic form of temperature
control. Chameleons take this principle several stages further.
Firstly
they bask Laterally. This means they position their body to be side
on to the sun thus exposing the maximum amount of surface area to
the heat source.
Pic of
cham by basking bulb side on
Chameleons also have hinged ribs.
This allows them to flatten their body thus increasing the surface
area of the side exposed to the heat source.
Pic here
of cham flattening ribs
In addition the chameleon will darken the side exposed to the heat
source to increase heat absorption and may lighten the opposite side
to retain heat once absorbed.
Pic of
cham in dark colours ie basking first thing
This lightening
of the side in shade also acts as camouflage as any predator looking
from below the chameleon would find the lighter side harder to see
with the light behind it. This "light underside" principle
is the same as most frogs and birds use.
After changing
the shape of its body and altering its colour the next stage is to
alter the blood flow rate. The Chameleons heart beats significantly
faster when warming up than when cooling down. This results in the
increased heat transfer between the warm surface and the cool core.
Once the P.O.T. is achieved the heart rate slows down to reduce heat
loss and the chameleon begins the daily task of hunting for food.
Reaching the P.O.T. positively and directly influences the Chameleons
ability to hunt, capture and digest prey.
A Chameleon at its P.O.T. moves quicker, is more accurate with its
tongue and has faster and more efficient digestion than one that is
below the P.O.T.
Thermoregulation
in unwell Chameleons
Chameleons
like many other reptiles thermo-regulate differently when ill.
An ill Chameleon will increase it's basking thus raising its body
temperature to above the usual P.O.T. They are effectively giving
themselves a fever, which aids the efficiency of their immune system.
In very
serious or more advanced cases of illness a sick Chameleons will often
seek out the coldest darkest area of the enclosure and stay there
Often refusing to more regardless of stimuli or enticement offered.
It is believed that the stress from the illness plus any previously
suppressed stress (could be environmental
or social or both) acts to suppress the immune system. To allow the
immune system to gain control again the chameleon must shut down as
many of its systems as possible to protect its self from further harm.
It should
be noted that this is absolutely not a recommended method of treating
a sick animal but rather the animals final attempt to gain control
of an illness which is already at an almost fatal level.
Creating
a basking spot
Changing the wattage of a bulb used to create a basking spot directly
effects the light and heat at the basking spot.
When creating a basking spot the aim is to create a bright area as
well as a hot area as reptiles associate bright light with heat. If
a dimmer stat is used with for example, a 100w bulb the bulb may only
be burning very slightly for the area beneath it to reach the required
temperature and consequently would produce very little light. It would
also gradually warm up the rest of the enclosure resulting in a reduction
of the thermal gradient therefore effecting the animals ability to
thermo-regulate properly.
A better option would be to use a lower wattage bulb that needs burn
brightly all the time to achieve the required temperature which consequently
would also create the desired bright spot as well.
Often the wattage of the basking bulb needs to be changed throughout
the year. A small wattage bulb is usually used during the summer where
there is naturally a higher ambient temperature and a higher wattage
bulb for the winter.
A
thermostat should be used in all cases to control the maximum temperature
at the basking spot, particularly as Montane species have a tendency
to cook themselves if basking spot too warm.
Remembering
chameleons are lateral baskers, the spot light should be angled.
Thermogradient
A typical
chameleon set up is shown below. The diagram shows how a bulb can
be used to create a thermal (heat) gradient.
Notice
the UV source is very close to the basking bulb so when the chameleon
basks to warm up it will receive the highest level of UV as it would
do naturally when basking in the sun.
A
- This area is too hot for the animal to enter.
Perches/plants should be kept away to avoid
the risk of thermal burns to the animal.
B
- This area is termed the "basking area"
and
represents the maximum safe temperature
where the animal can quickly heat up
until its body achieves the desired temperature.
This maximum temperature is species specific.
C/D-
The animal will spend most of its time in
these areas once its body is warm enough.
E
- This area is effectively unheated and should
always be sufficiently cool for the animal to be
able to retreat to on hot days. Ideally there
should be around a 20 degree difference
between areas B and E.
1
- Perch 1 allows basking and high UV exposure.
The left of the perch allows the animal to cool
off slightly but still allows high UV exposure.
2 - From right to left on Perch 2 both temperature
and UV exposure reduces.
3 - Perch 3 allows the animal to cool down when
the ambient temperature is too hot but will not
offer any UV exposure.
In the
above example a normal household pearl spot bulb was used. We find
a normal tungsten bulb adds parts of the spectrum that UVB Flourescent
bulbs do not produce therefore giving a more natural light.
Note: Area E can only be the same temperature as the surrounding
ambient temperature. This will go up and down according to the temperature
of the room it's in. If it measures 70°F during the winter and
the temperature in the room goes up to 90°F iin the summer the
coolest spot is also going to be 90°F.
This might sound obvious but we get e-mails all the time quoting
cold temperatures which have only been measured once. They are amazed
when they measure it again and find the don't have a cool area anymore.
Unless your room is air conditioned its going to vary. Don't guess,
always use a thermometer and measure constantly as well as maximum
and minimum temperatures.
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