Migration Flashcards
What is migration?
It is the directed locomotory activity of an animal during long distance journeys
What are the two types of migration?
- Periodic migration- population expansion
- Seasonal migration
Examples of periodic migration
-Lemmings migrate in large numbers when population expands
-Desert locusts migrate periodically following population expansion
What is seasonal migration?
It involves the migration between breeding area and over wintering or feeding area
Seasonal migration is seen in which animals
-many birds
-some fish
-insects
-reptiles
-mammals
Examples of migratory birds in Ireland
-Berwick’s swans
-Corncrake
Examples of champion migrators include
-Arctic tern flies
-Monarch butterflies
-Wildebeest
-Gray whales
What is homing?
It is the ability of an animal to return to a specific set point
What are some examples of specific set points animals return to?
-Daily return to nest or hive
-return by turtles to natal beach
-return by salmon to natal stream
How does homing occur in sea turtles?
They return to the beach on which they hatched after thousands of km migration
Why do animals migrate?
Animals that migrated may have left more offspring than if they did not migrate (benefit outweighs cost)
What are the costs of periodic migration?
(when is periodic migration undertaken?)
As the population expands locally ->overcrowding
Periodic migrations are often undertaken when population expands locally so that animals experience overcrowding, and can do better by moving elsewhere
In seasonal migration, animals move to track changes in the environment, what animals is this seen in?
- Monarch butterflies migrate south for warmth in winter
- Wildebeest follow the seasonal availability of water
What are the costs of migration?
- There is a high mortality rate due to exhaustion and predators
- There are also energetic costs
What are some reasons for the high mortality risk during migration?
-Difficulty finding food/water while travelling
-Collision with obstacles
-Storms
What are the benefits of seasonal migration?
-Energetic benefits
-Reduction in competition
-Reproductive benefits
-Protection from predation by swamping predators
What are the reproductive benefits in gray whales and salmon?
It brings both sexes together and provides a safe environment for young
What are the reproductive benefits of birds breeding in the north?
There is longer day-length for feeding and there is a seasonal high availability of food for young
What are the energetic benefits of migrating south in winter?
- Avoiding temperature stresses and associated metabolic costs
What does protection from predation by swamping involve?
-Huge number of birds available at one time during short breeding season, probability of taking one bird is small
-Predators deprived of prey when birds leaving breeding area, population expansion is limited
Types of orientation used in migration and homing
-Pilotage
-Compass orientation
-True navigation
What is pilotage?
Steering a course using familiar landmarks
What is compass orientation?
It is the ability to head in a particular compass direction without reference to landmarks
True navigation
-ability to orient towards a goal without landmarks and regardless of direction of goal
-requires both compass sense and map
-animal must know where it is relative to destination
-existence of map sense is controversial
What are the genetic controls of migration in birds?
-Whether to migrate
-Direction
-Distance
-Time of migration
What do breeding experiments show about robin migration?
80% migrate and 20% don’t
- they show that migration tendency is under polygenic control
What triggers the timing of seasonal migration?
Endogenous circannual rhythm (clock) entrained by photoperiod (daylight)
What is migration restlessness (Zugunruhe)
Most restless when weather is suitable for flight
Initiation of migration is triggered by
-accumulation of sufficient fat
-appearance of favourable weather conditions
Findings of experiment by Kramer to show the use of sun compass by starlings
-Starlings trained to look for food in a particular compass direction
-Time-shifted: artificial light regime reset internal clock by -6 hours
-Birds trained to find food in North
-Normal birds look for food in the north
Nocturnal migrants
-use sun
-fly in constant direction until daylight
