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Migration
Background
Information
As
Robert Knecht travels across North America, he will explore how people arrived
at the places they are.
People and wildlife have moved to suitable locations throughout time.
One type of movement is called migration.
Migration is the periodic movement of animals from one area to another
and back again as a natural part of their life.
Many people are familiar with the north and south migration of birds, but
migrations occur in many types of animals and have considerable
variations.
Types
of Migration
North/South
migrations are the most common. The
distances can be great or small. Birds,
monarch butterflies, sea turtles, and whales all migrate north/south, generally
between winter homes and breeding sites or to follow the rains and food supply
in desert climate areas.
High/low
elevation migrations occur in the mountains. Summer’s
warmer temperatures and lack of snow cover allow abundant food at high
elevations.
Cool temperatures and deepening snow force some animals to lower
elevations in the winter to find food and shelter.
Elk, big horn sheep, and mountain goats all exhibit elevation migration.
Many
bat species migrate laterally.
They move to breeding and feeding areas in the summer and to caves (at
the same or higher elevations) for winter hibernation.
How
Migration Occurs
What
causes migration and how animals navigate are areas of continual research. Causes can be temperature, water availability, and food
availability. Alone or in
combinations, these factors awaken natural instincts in animals to move.
Some species might learn the route by following others that have made the
journey before while others successfully make the journey on their own the first
time. Magnetic fields, stars,
smell, and physical landmarks are all possible keys to route finding.
Research is ongoing to unravel the mysteries of migration.
Banding,
tagging, and radio tracing are common methods of tracking individual migrators. Banding and tagging involve attaching a number to the animal.
The band/tag number and location are filed in centralized computers.
Instructions on the band/tag tell anyone that finds the animal again,
alive or dead, where to call and make a report. In this way, the movements of an animal can be tracked over a
long period of time -- assuming the banded/tagged animal is recaptured!
Radio tracking involves attaching a battery operated collar to the animal
or inserting a small radio emitter under the skin.
Both devices emit a frequency which scientists can pick up on a radio
receiver. This method retrieves more information in a shorter period of
time but is more expensive in equipment and is more labor intensive.
Human
Migration
Early
humans also migrated, generally to follow animals used as food that migrated as
well.
It was not uncommon for many Native American, African, and Australian
tribes to have summer and winter hunting grounds.
Improved food preservation techniques and the advent of farming made
human migration less necessary. Today,
true human migrations are seldom necessary.
Migration
Challenges
No
matter how or why an animal migrates, migration is always dangerous and many
individuals do not complete the journey. Limiting
factors to an individual animal’s success can be natural or human created and
include such things as power vehicles (cars, boats, planes), power lines,
hunters, pesticides, storms, food, water, and tall buildings.
Nevertheless, migration is a fascinating and mysterious part of the life
cycle of many species.
Vocabulary
Migration
- the periodic movement of animals from one area to another and back again as a
natural part of their life.
Limiting
factors - influences in the life history of any animal, population of animals,
or species including such things as food, water, shelter, space, disease,
predation, climatic conditions, pollution, hunting, and accidents. When
one of these exceeds the limit of tolerance of that animal or population, it
becomes a limiting factor. Limiting
factors may result from causes in nature as well as human activities.
Life
cycle - the continual sequence of changes undergone by an organism from one
stage of life to the development of the same stage again.
Fun
Fact
The
Arctic tern is the champion migrator. It
flies between Greenland and the northern Arctic shores, down the length of the
Atlantic Ocean and all the way to Antarctica and the South Pole - a round trip
flight of 22,000 miles every year.
Other
Resources
Bat
Conservation International
Center
for Marine Conservation
Colorado
Bird Observatory
Cornell
Laboratory of Ornithology
Monarch
Watch
National
Audubon Society
Project
Wild “Deer Crossing” activity
ACTIVITY
ONE
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