People and animals follow the rhythms of day and night, which are caused by the earth's rotations of approximately 365 times a year. While we are making this journey around the sun, the earth tilts on its axis, giving us our four seasons.
Animals live according to this rhythm of the seasons. Breeding, raising young, family breaking up and preparing for the winter season by either migrating, hibernating or putting on extra fat and heavier coats are all done due to this rhythm.
On a previous visit, Hurricane Sandy came up the coast and Rehoboth Beach was evacuated. Later Sandy slammed ashore at Atlantic city causing a lot of damage because the moon was in its full moon stage, causing 20% higher than normal tides.
The tides are caused by the pull of the moon, and as the earth rotates, the tides are carried to each shore in turn. Because of the monthly travel of the moon around the earth (every 27 1/2 days), the moon is overhead at a particular place on earth 50 minutes later each day. As a result the tides also come 50 minutes later each day. There is a high tide and a low tide occurring approximately every 12 1/2 hours. Creatures living in and along the seas and oceans live according to this rhythm of the tides. If you were to take a walk on the beach during low tide, many barnacles would be found. At low tide, sandpipers and fiddler crabs appear on the sandy beach in search of food; however, the barnacles aren't available to them because they have sealed themselves tight, and it is almost impossible to pry a barnacle (a small marine organism with a shell) open. Later, at high tide when the barnacles are covered with water, the shells have opened for feeding.
The fiddler crab changes color according to the time of day. In the morning, the crab, has a silvery gray skin, and then, as the day goes on the fiddler crab's skin begins to darken. At noon, the skin is at its darkest, and from noon on, the skin begins to lighten until sunset when it again becomes a silvery gray. There are some people living along the shore that can actually tell the time of day by the color of the fiddler crab. Scientists believe the dark skin protects the crab from the sun's hot rays.
One might think that this change in color occurs because of the sun; however, in a study done on fiddler crabs that were taken from the beach and put in a completely darkened room, the fiddler crabs continued to change colors according to the schedule followed on the beach. (Scientists believe the fiddler crabs have an inner clock, which keeps them in step with the 24 hour clock.)
In another study, creatures (such as bees) that were taken to new locations re-set their clocks according to daylight. The 13 and 17 year cicadas (locusts) have an internal clock, which causes them to appear after spending years underground. After many years, an internal clock brings salmon back to their birthplace to spawn. We humans also have this inner clock and even a one hour change will be noticed. Those who travel for great distances are said to have jet lag until their inner clocks are reset.
Light and darkness and seasons govern the lives of animals by day and by year. Some are sent on long journeys, while others go into deep sleeps and still others put on heavy coats and extra body fat. They are acting according to their internal clocks set by the earth, moon and sun.
One of the most remarkable time keepers is the grunion, a small fish that lives off the coast of Southern California. Twice every month (once at full moon and once at new moon) there is an extra high tide, and during these tides, the waves go farther up onto the beach than at any other time. The grunions ride the waves of these extra high tides and lay their eggs on the beach at the highest point reached by the water. In 15 days, at the second extra high tide, as the water reaches the eggs, they hatch, and the young fish swim away.
A sea worm that lives in the waters off the West Indies coast also has an accurate inner clock. Each October when the moon is just into the third quarter, the sea worms swarm on the surface of the Atlantic Ocean. To attract the males, the female worms give off a glowing light. On one of the journeys Christopher Columbus made crossing the Atlantic Ocean, he wrote in his journal, on October 11, 1492, that mysterious lights were seen on the ocean. From the date recorded, we now know that the lights were from the swarming female sea worms.
We humans also have inner clocks for acclimating to temperatures and elevations. In the fall, when Mary Alice and I go for our morning walks, we feel a chill when the temperature drops to the 40's; however, a few weeks later 40 degrees feels warm.