Summary
Cycles of behaviour, daily (circadian) and seasonal, tied to light and temperature.
In depth
Circadian (about 24 h), circannual, tidal and lunar. Endogenous clocks are reset (entrained) by zeitgebers such as light.
Endogenous rhythms persist without cues and are reset by environmental signals, so they are not simple responses to the environment. Free-running periods in constant conditions are slightly different from 24 hours.
Example: hibernation timing and bird breeding are circannual rhythms.
Biological rhythms are regular cycles in physiology and behaviour. Circadian rhythms last about 24 hours, circannual rhythms about a year, and tidal and lunar rhythms follow the sea. They persist in constant conditions, showing an internal clock, but are reset (entrained) by cues such as light.
In mammals the suprachiasmatic nucleus in the hypothalamus is the master clock, controlling melatonin release from the pineal gland. Clock genes such as Per and Clock run feedback loops about 24 hours long.
Example: jet lag arises when the internal clock is out of step with local time.
Remember: rhythms are endogenous, not simply a reaction to light and dark.
Frequently asked questions
What is Biological Rhythms?
Cycles of behaviour, daily (circadian) and seasonal, tied to light and temperature.
Which area of biology covers Biological Rhythms, and how advanced is it?
Biological Rhythms is one of the 53 topics in Animal Behaviour. It is rated Beginner, so it suits learners who are starting out in biology. Related topics in this area include Chronobiology, Migration Behaviour, Nature vs Nurture.
Can you give an example of Biological Rhythms?
Fiddler crabs show tidal rhythms in a lab with no tides.
What should I learn before Biological Rhythms?
Biological Rhythms is a Beginner topic, so no earlier topic is required. Other Beginner topics in Animal Behaviour that pair well with it include Animal Behaviour, Innate Behaviour, Learned Behaviour.
What topics are related to Biological Rhythms?
The closest topics to Biological Rhythms are Chronobiology, Migration Behaviour, Nature vs Nurture, Collective Behaviour. Comparing them side by side is a good way to see how the ideas connect.
How can I check that I understand Biological Rhythms?
Read the summary and the in-depth section, then use the quick check on the interactive lesson for Biological Rhythms. To practise the whole of Animal Behaviour, use the Animal Behaviour quiz.
How is Biological Rhythms different from Chronobiology?
Biological Rhythms: Cycles of behaviour, daily (circadian) and seasonal, tied to light and temperature. Chronobiology: Studies endogenous circadian clocks and how they synchronise behaviour to the environment. Read both side by side and note what each one explains.
How should I study Biological Rhythms step by step?
First, read the summary and write the definition in your own words. Second, read the in-depth section and note any example. Third, compare it with Chronobiology and explain the difference aloud. Finally, take the Animal Behaviour quiz and come back to this page for any question you miss.