Migration

It occurs in mammals, fish, birds, reptiles, amphibians, insects, and many invertebrates. Most do it to take advantage of conditions in a habitat, often changing with the seasons.

Types of Migration

Latitudinal

These are migrations that move in a northern or southern direction.

Altitudinal

These are migrations that involve a change in altitude.

Example: Dall sheep summer near the top of mountain ranges and winter at lower altitudes where the weather is less severe.

Seasonal

Most migrations correspond to a change in seasons.

Reproductive

This type of migration occurs when animals choose a different habitat for bearing young. For some this corresponds with a return to where they were born.

Others find conditions in their preferred adult habitat not as conducive to raising young, so they move to an environment that may be warmer, have fewer predators, etc.

Example: Salmon are born in freshwater streams and migrate to the open ocean where food is more plentiful to mature, they then migrate back to the stream they were born in to produce their own offspring.

Complete migration

This means that all individuals within a species migrate without fail.

Partial Migration

This means that some individuals may choose not to migrate while others do.

How Do They Know Where To Go?

Animals use a variety of different cues to navigate. They may use visual cues such as landmarks, solar cues, and even the position of the stars. Others use olfactory and geomagnetic cues to orient themselves.

While some animals will migrate many times over a lifetime, others may only do it once. Some dragonfly species may actually go through four generations over a single round trip migration.

Scientists believe that they follow the rainy weather from southern India to eastern and southern Africa. This means that the round trip is about 14,000 – 18,000 km.

This is more than double the distance travelled by Monarch butterflies, who also take multiple generations to complete a single migration from southern Canada to Mexico and back.

The Most Impressive Migrators

The dragonfly migrations are impressive but the arctic tern wins for the longest roundtrip migration, travelling over 80,000 km a year. Longest single flight with stops goes to the bar-tailed godwit, a bird that crosses the Pacific Ocean in a marathon flight lasting approximately 9 days.

The smallest migrants are species of zooplankton that are only 1-2 mm long and vertically travel up and down the water column to different habitats. The largest is the blue whale which can be 24-27 m long.

The longest mammalian migrant is the humpback whale which makes a round trip of about 17,000 km.

While animals migrate for a number of reasons, the single-minded devotion they display during migration and their ability to navigate over long distances remains an extremely impressive feat.