Analysis of wild tortoise (Testudo graeca graeca) temperatures using thermal imaging

Two images are taken simultaneously, a high resolution thermal image (320 x 240) and a visible light image.

Visible light:

Visible light image

IR image:


These can be 'overlaid' and blended to produce a variable transparency composite which can help with analysis:

IR Visible light blend

The images shown here are at far lower resolution than actually generated, and the images are only a small part of what is captured.
Most of the information is 'hidden' in the files generated and this can then be analysed in specialist software in various ways to reveal in
great detail what is going on. For example, here we have a wild tortoise that was observed grazing. The IR images reveal the extraordinarily
even heating pattern typical of reptiles after solar basking. The heat is not concentrated in the surface tissues, but infuses the entire body. This
is a characteristic property of WiRa radiation as occurs naturally in sunlight.

It is most obvious here, in the neck/shoulder area. An area of high blood flow and which is also indicative of core temperatures:

Shoulder area

(the blue line over the head is a cooler stalk of vegetation)

It can be useful to analyse small segments of the image. This can reveal the degree of solar gain over surface/ambient temperatures
and can also generate max-min-average figures for various body parts.


We can also look at one particular body part in detail. Here, the underside, or plastron. One question that is often asked is
"How does the plastron get warm? From contact with warm substrate or via the carapace/limbs when basking?"
Careful analysis of a series of IR images provides an answer. During basking phases the prime source of plastron heat is direct
from the body, with only a small influence as result of contact or reflected thermal radiation from the surroundings. One thing that
we have learned is that tortoises are incredibly efficient 'solar collectors' capable of very significantly raising their body temperatures
above ambient, even in overcast conditions. They also use their limbs (and extended neck) to direct solar energy right into the bloodstream,
functioning as a very effective 'heat pump'. This almost certainly has important implications for the vitamin D3 metabolism.


Heat distribution in plastron zone:

Heat distribution plastron
All images (C) 2014 Tortoise Trust