It is not known exactly what causes an animal to begin hibernation or end it, although a sudden fall in temperature is the most obvious. It is likely that hibernation ceases when the average air temperature rises above a certain level in Spring. Should a period of cold weather then return, the animal will resume hibernation until conditions improve. It has been observed that early nesting birds will abandon their nests and contents if weather conditions do not provide them with food for their expected off-spring.
Brimstone Butterfly
Red Admiral Butterfly
Images by K Wilcox
