What are circannual rhythms?

A circannual rhythm is like a yearly timer that tells animals when to sleep, wake up, or change their behavior.

Imagine you have a favorite toy that only works on certain days of the year, maybe it’s your favorite video game that you can only play during summer break. That's kind of how some animals feel. They have a circannual rhythm inside them, like a tiny clock that ticks through seasons.

Think about a bear hibernating in winter. The bear doesn’t know the temperature outside, it just knows it’s time to sleep because its body tells it so. This is all part of its circannual rhythm, which helps it prepare for long winters without food.

Some birds fly thousands of miles every year, and some frogs change color with the seasons. All these things happen thanks to their circannual rhythms, like having a built-in calendar that helps them know when to do what!