Heating and Lighting | natural-iguana

Going back to basics!

Thermal Importance and its implications in enrichment, updating discussion relating to temperatures.

Reptiles are ectothermic which simply just translates to (cold blooded). This just means reptiles have evolved to become primarily depend on external sources of heat (which is strongly associated with light intensity) energy in order to function at the most basic level. Not only is thermal input responsible for facilitating metabolic heat, digestion, locomotion and activity to or away from resources, it allows for a range of behaviours including, predator avoidance, aggression reproduction, and social play outs among conspecifics, but less discussed also helps with disease resistance implicating immune response. Basking is the most obvious sign associated with this, movement or advancing towards warmth and cooler areas - isn't only the most basic thing every owner can provide but it is also the least difficult in modern times.. (Cosquieri 2019) Accordingly, this has been argued to be the strongest type of enrichment for any reptile species. The explanation behind this is profoundly associated with how reptiles work and move. Each specie has their very own Tp (favoured temperature). But, the issue with accepting this value as a stable source of heat under captive conditions is comprehending what this favoured temperature is, because Tp can shift throughout the day time between different sexes at various occasions of year, at various ages, when foraging and yes, also throughout reproduction and daily activities (territorial patrolling etc)

(Vitt and Caldwell 2014) Outline some thermal ranges reptiles exploit irrespective of most commonly kept species or types.

For example. A green iguana may wake up early in the morning, in my experience they do this about half an hour before the lights go on. In the wild they move to the outer edge of the tree branches where they may position themselves perpendicular or (paralell) to the direction of where the sun rises, extension of the dewlap occurs, which acts somewhat as a solar panel. Within this thin flap of skin are blood vessels,, causing heat to radiate energy and is absorbed through the dewlap which in turn starts warming the blood vessels within, the blood is then pumped around the body by the heart, thus somewhat warming the core temperatures of the lizard as well as the external temperatures across the body. At the same time, these lizards are capable of altering colouration in order to be able to absorb or pull more heat to the skin, or to reflect it, this is called conduction and convection through radiation, (I have only seen this behaviour under outdoor conditions) this simple but marvellous adaption, simply works on the principle, that darker colours will conduct heat, (similar to us wearing a black t-shirt on a hot day) and convection, which means altering the colour to a lighter shade will help reflect some of the heat away.

Once the iguana has achieved a desired temperature, it may move more into the interior of the tree branches or vegetation in order to feed, or graze, meaning a different temperature will be intercepted both from the shaded tree trunks, and from the drop in ambient temperature. If at any point, the lizard feels threatened, it may invoke tonic immobility (Greene et al., 1978), or simply drop off the tree perch into a nearby water source, exposing it to a very different range of temperatures, meaning, it must again resurface in time and warm itself back up.

If this iguana however carries stripes, or natural dark spots or stripes, this too, may have implications on the effectiveness between heat exchange from environment to body both through radiance and thigmothermy. An iguana, on the ground, as can be observed in my female iguana here, is partially exposed to light, and shade at various locations due to the gaps between the leaves. She is of course, intercepting a delicious leaf of slender leaf of plantain in the orchard, but for this few seconds, she is exposed to a very different set of temperature to what she was basking in only a moment before hand. Showing that her preferred temperature at that moment in time has shifted.

This microclimate is based on something called LAD (leaf area density) and leaf scatter illumination. Many tree dwelling lizards use this both on the ground and in the trees. (Seigel and Collins, 1993)

Downpour of rain, may also influence temperature variable, as well as wind, and other weather behaviour, therefore, temperature fluctuation, likely has an impact on locomotive and thermal decision makers of the lizard too.

The wild animal is quite active, and thermal implications exist primarily toward behavioural decision makers which will largely be temperature dependent. As we can see, exposure to a wide variety of temperatures likely exists for our scaly companions.

As I am sure we all know, Iguanids are diurnal (active during the day) sunlovers, termed heliotheric species, or heliotherms, (Avery RA. C Gans. 1982) meaning they depend heavily upon external sources of warmth naturally to warm up. (Primarily through the sun) They are poikilothermic, or poikilotherms which simply just means they are capable of behaviourally deciding which temperature ranges to intercept and when. Bradymetabolic, meaning they have a lower resting metabolism at low temperatures. Thigmothermic translates to gaining heat directly from contact with a physical object, (belly heat) (Library.iucn-isg.org, 2019)

The thermal complexity of environments in which these animals naturally live has often gone under appreciated in herpetocultural literature, in the interchange between a range of temperature shifts it makes this difficult to offer a one size fits all answer for all species and even all individuals within a species but I myself try to focus on the voluntary minimum and maximum temperatures a species orients towards through my own keeping observations and research. A reptile's favoured temperature does not for the most part always mean it is the ideal temperature for all of its natural bio performances yet we should begin to look at it as they are dependent upon a range of temperatures to exploit them all (Vitt and Caldwell, 2014) other factors can influence it and how the reptile thermoregulates, and finally we should consider where it decides to thermoregulate. (In the tree canopies. Iguana iguana, or in more fossorial or terrestrial sp Dipsosaurus dorsalis for example. In the interchange between this, arboreal species may surface to the ground on certain occasions, and fossorial or terrestrial species may seek higher elevations upon rocks or lowland shrubs in certain situations.

Most reptiles move along a surface or varying elevations of perch sights at different times of the day. They may withdraw from warmth at certain occasions, and search it out at others. Offering them an increase in choice for intercepting different temperature ranges is the whole point of recreating a thermal gradient in captivity, and applying wild values observed in natural history into our enclosures.Traditionally much iguana iguana literature suggests that a basking temperature of between 30-35c or 86-95f is optimal for this species, commonly termed POTZ (preferred optimum temperature zone) with the lower end capable of facilitating digestion also.

My keeping observations.

Back in 2012 during a summer day observing and measuring my own iguanas in the outdoor live planted hawthorn enclosure I decided to play around with my temperature gun and thermometers while simultaneously observing their conduction and convection method of going darker and lighter, this is a common behaviour which is thought to help them pull more heat to the skin and when going lighter assists in reflecting it. I was surprised to find my iguanas (although admittedly) only for short time periods were exposing their temperatures to far greater ranges deliberately than had been published in any literature I had read. At the extreme end my male was at 40-43c or 106-109f externally (at least) for an approximate 20 minutes before retreating to shade. Some of the females achieved a 38-40c roughly 100-105f within this time set before retreating to shade and beginning to graze on the hawthorn. At 10 o’clock I checked them all, two females were at a 38c still, one was at 33c but admittedly she was smaller and at a lower level than the others. My male was also at 37c. At midday I checked them again and found them all as usual in the shade and at a much lower level with mouths open attempting to cool down, I measured them all at 38c for the males and 35c for the females, but I gave the enclosure a hose down, this seemed to stimulate foraging activity (possibly in an attempt to get some cooler moisture) at 2 o’clock in the afternoon I found my male back perched at the top, one female was partially in and out of the foliage, their temperatures all measuring 35c. The point I want to bring attention to here is that a wide range of temperatures were intercepted that day, and roughly at the same time with the only real difference being their sexes and ages. In my experience even here in the dull rainy UK, iguanas can and will intercept temperatures far greater than traditionally thought of as “optimum temperatures” I then decided to include higher 40c basking spots into my indoor enclosures. Depending on the design, in my largest enclosures I currently have multiple bulbs of different wattages appropriately distanced to recreate a range between 30-35-40c which in turn allows my iguanas to intercept a set of different temperatures at different times across the highest points. The air ambient temperature is often between 23 26c, and my night time temperatures can fluctuate depending on if I have the heating on or not, 20-23c In and of itself this provided my iguanas the choice to intercept different temperatures at different times to move between or away from a heat source if they so wish to cool down. This should encourage more normal activity behaviour patterns, locomotion and therefore exercise and thus promotes physical fitness.

It has long been known in herpetculture that a sick reptile may benefit from increased basking temperatures ( Barten, S. (1993). There is every possible chance that a reptile will know it is sick before the owner does, in my own mind, providing appropriate space of the enclosure permits safe high ranges with cooler areas to escape too, I have no reason not to provide these as from my observations higher temperatures are frequently intercepted by my iguanas. When you see this

behaviour across 13 at any given time outdoors split out over 100 over the years, it is a fair assumption to say that this is a very deliberate behaviour and is likely serving a purpose if only for 20 minute periods.

My keeping observations.