You will be familiar with the phrase ‘cold blooded’ to describe reptiles and amphibians. When the temperature is cold reptiles and amphibians literally are cold blooded but when the temperature warms, so too does the temperature of their blood. Ectothermic more accurately describes the internal workings of a reptile or amphibians circulatory system. An ectotherm has little if any way of producing its own body heat and so relies on external factors in order to reach its optimal activation temperature. Put simply, by basking in the sun they are able to warm themselves. The activation temperature varies from species to species, it must be reached in order to allow the animal to be able to hunt, mate, digest food and to carry out all it’s normal daily activities.
Earlier this month whilst out on the moors I came a cross several adders basking in the sun. The temperature reading in my van was 4°C, add to that a cold biting wind and it drops a few degrees more – Yet these hardy snakes were laying out on the ground. Admittedly they were sheltered by heather and bracken, but it was still cold. I was frozen.
This male adder, photographed on the 2nd March, is showing classic flattened basking behaviour.
By spreading out the ribs and flattening the body the snake increases its surface area exposed to the sun. This allows it to warm up more effectively especially on cooler days such as the conditions when it was seen. As with many Northern species of reptile the adder has a lot of dark patterning. Darker colours absorb heat more quickly and help animals in cooler climates to get active earlier. Reptiles in southern Europe for example are often highly colourful and will hibernate during the winter months even when temperatures are equivalent to a UK summer.
Lizards will also flatten their bodies when basking in early morning sun. As temperatures rise this flattening is decreased and once the lizard begins to move around they return to normal. Smaller juvenile lizards are naturally darker in colour and so they do not need to bask for as long as their paler parents. They do however bask more frequently as they cool down quicker due to their small size.
Once the external temperature gets too high, reptiles seek shade or shelter in order to maintain their temperature. They can overheat, a common cause of death in captive reptiles where they can not escape a heat source such as a bulb or mat.
Many people think you need hot sunny days in the UK in order to see reptiles but often the opposite is true. They can just as easily be encountered on cold spring mornings and overcast summer days.
Please remember to keep us informed of any reptiles you see while out on your wanders. This link will take you to our online recording form. Keep it in your smart phone or in your web browser favourites for quick and easy access;
John R Grundy
Revealing Reptiles Project Officer