Animal Migration
• Leaving an area for part of the year and
moving to habitats that are more hospitable.
• Migration is
– Predictable
– Seasonal
– Repeated each year
Animal Movement NOT Classified as
Migration
Dispersal:
– Animal movement caused by overcrowding
– Animal movement away from a group based on
sexual maturation.
• Example: Young male lions. All the females in a pride
Hypothesis:
Why
one
gender
are related.
As a would
male reaches
sexual
maturity, he
leaves his pride, and eventually finds another pride he
disperse
a group at sexual maturity?
can from
take over.
• Example: Female chimpanzees. Leave natal (birth)
communities between the ages of 9-14 years and join
unrelated communities.
Animal Movement NOT Classified as
Migration
Irruption:
– Animal movement out of an area at unpredictable
times due to harsh conditions or limited resources.
Example: Lemmings - “the Scandinavian lemming,
migrates in a huge group when food becomes scarce.
They will run in one direction through meadows,
woods and towns. If they come to a large body of
water they will swim and swim looking for land. The
stories about lemmings jumping off cliffs are a
myth”. www.mnh.si.edu/arctic/html/lemming.html
Why Migrate?
• To avoid seasonal variations in temperature,
snowfall, and water
• To take advantage of
– Food and essential minerals
– Available water
– Shelter
– Available mates
– Available breeding requirements
Types of Migration
• Latitudinal migration
– movement of animals north and south from
regions of cold in the winter to warmer regions
near the equator.
– this movement is reversed in the summer.
Types of Migration (continued)
• Altitudinal migration: the movement of animals
up and down major land features such as
mountains.
– In the northeast USA, altitudinal migration is not a
major factor in the movement of animals.
– In the American west, mountains are younger and
taller. There are great extremes between conditions
on mountain tops (alpine regions) and areas at lower
elevation.
• Examples: elk and bear move down mountain slopes to
where food is more abundant and snowfall is less.
Types of Migration (cont)
• Reproductive migration is the movement of
animals to bear young.
– The area may be safer for the young because of
fewer predators or more shelter from predators.
– An animal requires a different type of habitat
when it is young than when it is older. Examples:
grey whale, European toad, green turtle, emperor
penguin
Latitudinal Migration
• Why do animals return to their breeding
grounds in the spring?
– Food, shelter and mates become abundant in
their breeding grounds and competition is less
than near the equator.
– Day length increases at their breeding grounds (up
to 24 hours/day), which increases the hours spent
foraging.
– Day length is 12 hours/day year-round near the
equator.
Each Type of Migration Can Be:
• Complete migration
– Occurs when all members of a species leave their
breeding range during the non-breeding season.
– Many N. American song birds are complete
migrants.
– These birds winter in South and Central America,
the Caribbean, and southernmost parts of USA.
Complete Migration
• IN WHAT TYPE OF AREAS WOULD YOU EXPECT
TO SEE COMPLETE MIGRATION? AND WHY?
Most complete migrants breed in
northern temperate and arctic areas
(such as Alaska) of North America,
Europe, and Asia
Partial Migration
• Some, but not all, members of a species move
away from their breeding grounds during the
non-breeding season.
• This is the most common type of migration
Complete: Worksheet on Migration
What Triggers Migration?
• Trigger(s) one or more of the following:
– Shortening day length (end of summer) or
lengthening day length (end of winter)
– Decrease in food and water supplies
– Circannual rhythms – Important for birds
wintering close to the equator. At the equator
there is no change in day length or food
availability year-round.
Navigation and Migration
• Genetics plays a large role in migratory
behavior. Animals inherit migratory routes
from their parents.
• In short migrations or in altitudinal migrations,
animals follow
– food or water or
– head downhill in winter and back upwards in
summer.
Navigation and Migration
• In longer migrations animals orient
movement:
– Using the sun’s position in the sky and the time of
day (ex. Starlings)
– Using the stars of the night sky (mallard ducks)
– Using the geo-magnetic field (migratory birds,
salamanders, salmon, or hamsters, loggerhead
turtles.
Navigation and Migration (continued)
– Using mental maps based on eyesight (they
become familiar with an area)
Read:
Evidence
a navigational
map
stretching
– Using
mental for
maps
based on sense
of smell
–
across(fish)
the continental U.S. in a migratory songbird,
– Using subtle
changes in QUESTIONS.
water quality and
and ANSWER
'reading' wave and current patterns (aquatic
animals)
Adaptations for Migration
(examples)
• Birds – hollow bones
• Geese – fly in “V” to decrease wind drag
• Birds/whales– feed intensively before setting off
to lay down fat reserves as fuel – a form of
behavior called hyperphagia
• Radical physical transformation. Some birds
develop larger, powerful breast muscles for flight
and shrink non-essential organs prior to
migration
Surviving migration
• How do animals enhance thir ability to
survive a long-distance migration? They
– travel in groups for protection
– hitch a lift on ocean currents and winds
– stop en route to rest and refuel
Specific Examples of Extraordinary
Migrations
Monarch butterfly
Arctic tern
Monarch Butterflies
• A monarch butterfly’s life cycle includes four
stages: egg, caterpillar, pupa, butterfly
Monarch Butterflies
• Over the course of ONE year, four or more
generations of monarchs are born and die.
• The butterflies in most of the generations live
only 2-6 weeks.
• The butterflies that emerge in August from a
chrysalis are the ones which migrate. They live
6-8 months!
• Migration begins in late August from eastern USA
/Canada and ends in early fall in Mexico. 40-60%
die en route.
Monarch Butterflies
• Navigation: appears to be a combination of the
magnetic pull of the earth and the position of the
sun among others
• While migrating, the butterflies are in
reproductive dormancy. Their sexual organs are
not fully developed
• Upon arriving in Mexico, they settle on oyamel fir
trees.
• Tens of thousands of monarchs cluster on a single
tree to stay warm.
Monarch Butterflies
• When they arrive in Mexico, they feed and
then “hibernate”—low metabolism
• As temperatures increase (March), their
activity increases, their sexual organs mature,
mating begins, and they head north.
• Between leaving Mexico and returning to
Canada and USA, there will be 2-4
reproductive cycles.
Greenland
Arctic Terns
• Migration route is the longest of all animals
• In the summer months of the northern
hemisphere, the Arctic tern lives and breeds
near the north pole in Greenland.
• In the fall, it begins its flight to the shores of
Antarctica at the south pole. The terns will
reach Antarctica when summer begins there.
• Total round trip = 44,000 miles.
Antarctica
Arctic Tern
• On their way from Greenland south, they stop
for a month and feed
• On their return from Antarctica they follow
the winds--even though the trip is longer.
• Arctic terns live up to 34 years. Over their
lifetime they can fly more than 1.25 million
miles
• Amazingly each arctic tern has a mass of only
3.5 grams
Arctic Tern
• Navigation
1) The tern has biomagnetite in its brain. This
allows it to sense the surrounding magnetic field
and use it as a guide.
2) The tern uses landmarks, such as coastlines, to
help guide it.
3) During the night, stars and the moon can guide
the birds.
Problems for Migrating Animals
• Migration routes include multiple
countries/continents. Not all of these areas
provide safe habitats (wars/construction/habitat
loss)
• Climate change - has the potential to disrupt the
migratory patterns of a wide range of animals.
– loss of habitat for birds that breed on small ocean
islands.
– warmer temperatures may cause a change in the
seasonal availability of food for migrating animals.
READINGS
Choose a Migrating Animal:
–
–
–
–
Sea turtles
Denali Golden Eagles
Rocky Mountain Elk
Ruby throated
hummingbird
• Follow guidelines with your
group for presenting the
material to class.