A short video I took the other day for fun is at the bottom of this post.
I took some temperature readings of my collared lizard outdoor terrarium, which I specially designed and built to keep my collared lizards outdoors year round here in central Virginia.
It was 55 degrees and sunny with some clouds at the time I recorded this.
At the time, I didn’t understand why my lizards were recording temperatures well in excess of 100 degrees, yet the rocks were 100 and below.
After thinking about it, I believe I understand what was happening.
The thermometer is recording surface, not core temperature. Because the rocks have more mass than the lizards, the core and surface temperatures of the rocks are heating up more slowly in the sun. The core temperatures of the lizards are probably still a bit cooler than their surface temperature and limbs, and the temps recorded as high as 106 were surface temps of the skin rather than the core temperatures of the lizards.
When I get another day like this, I’ll test this idea (maybe not until next year– as the weather warms, the rocks in the terrarium will be warmer than the lizards, because the lizards will move in and out of the shade to stay cooler).
I will do this by picking the lizards up and recording the surface temperature of their bellies. If I’m correct, their ventral surface should be closer to the temperature of the rocks they are on.
It is pretty interesting to me because it shows these lizards are really good at using the sun to warm up even when the weather is cool, better at it than the rocks they are sitting on.