Migration
Directed locomotor activity of an animal during long distance journeys
Periodic migration
Exploration/ population expansion
Seasonal migration
Typically involves migration between breeding area and over wintering or feeding area
Examples of periodic migration
Lemmings migrate in large numbers when population expands
Migratory birds in Ireland include
Bewick’s swan
Corncrake
Homing
The ability of an animal to return to a specific set point eg return to nest
Why are pigeons used when studying homing
- easy to handle
- not dependent on season
Why migrate?
Periodic migrating animals move to prevent overcrowding
Seasonal migrating animals move to track changes in the environment
Cost of migration
-Mortality risk: Loss of animals due to exhaustion, predators, storms
- Energetic costs: need to build up body fat by 30-40% before migrating
Benefits of seasonal migration
- Energetic benefits: moving south in winter to avoid temperature stresses and associated metabolic costs
- Reduction in competition
- Reproductive benefits: breeding in north, longer day- length for feeding
- Protection from swamp predators
Pilotage
Steering a course using familiar landmarks
Compass orientation
Ability to head in a particular compass direction without reference to landmarks
What can you use for compass orientation
Suns
Stars
Earth’s magnetic field
True navigation
Ability to orient towards a goal without landmarks and regardless of direction of goal. Requires both compass sense and map
Genetic control of migration in birds
- Whether to migrate
- Direction
- Distance
- Timing of migration
Timing of seasonal migration
Modified by:
- External factors eg weather
- energetic condition of bird
When do birds learn to use a stellar compass but not the actual patterns of stars
During a sensitive period between leaving the nest and starting the autumn migration
How is use of star compass learnt
Young birds learn to recognize constellations that move least
Magnetic sense in birds
- Beak region: receptor based on magnetite crystals
- Eye: photochemical system
How pigeons use odor map to navigate
- Learn odours at home
- Use odour bouquet and wind direction to locate home when displaced
Mechanisms of long distance orientation in birds
- Orientation by landmarks
- Sun compass
- Polarised light
- Star compass
- Magnetic compass
- Odour
Where do fish usually migrate to?
- Within seawater
- Within freshwater
- Between sea and freshwater
What is smolt transformation
Morphological, physiological and behavioral changes preparing for move to sea. Under control of thyroid hormones
How do salmon find their way back to their natal stream?
- Open sea navigation; sun position, polarised light patterns, earth’s magnetic field
- Homing: once at coast locate the exact stream in which they hatched
