Migration Types
Migration can be either obligate, meaning individuals must migrate, or facultative, meaning individuals can choose to migrate or not.
Within a migratory species or even within a single population, often not all individuals migrate. Complete migration is when all individuals migrate, partial migration is when some individuals migrate while others do not, and differential migration is when the difference between migratory and non-migratory individuals is based on age or sex (for example).
While most migratory movements occur on an annual cycle, some daily movements are also referred to as migration. For example, many aquatic animals make a vertical migration (Diel vertical migration), travelling a few hundred metres up and down the water column. Similarly, some jellyfish make daily horizontal migrations, traveling a few hundred metres across a lake.
Read more about this topic: Animal Migration
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“If there is nothing new on the earth, still the traveler always has a resource in the skies. They are constantly turning a new page to view. The wind sets the types on this blue ground, and the inquiring may always read a new truth there.”
—Henry David Thoreau (1817–1862)