Biology September 2013 | Page 12

BEHAVIOUR

FOR

MAINTENANCE

Rythmic Activities

Daily cycles are known as circadian rhythms, and many animals will alternate periods or activity and inactivity on a daily basis.

For example some animals are nocturnal (active at night) and thus are resting (inactive) during the day, compared to diurnal animals (active during day), which rest at night. The rhythms of animals can also be affected by tides and lunar cycles. Circannual rhythms are yearly, such as the annual migration of many species of bird, stingrays and whales.

Vertebrates have ‘internal clocks’ which are caused by the levels of melatonin in their blood. In the absence of bright light, melatonin is produced thus reflecting the time of day to be night.

"A circadian rythm is a daily change and a lunar cycle happens along with the waxing and waning of the moon. A circannual cycle refers to a yearly rythm."

11