MIGRATION Flashcards
Migration
directed locomotory activity of an animal during long distance journeys
Periodic migration
Exploration/population expansion. E.g. lemmings, collared doves;
locusts, aphids
Seasonal migration
typically involves migration between breeding area and over wintering
or feeding area. Typical of many birds, also seen in some fish (salmon, eel), insects (e.g.
monarch butterfly), reptiles and mammals (e.g. wildebeest, gray whales).
Homing
The ability of an animal to return to a specific set point (e.g. daily return to nest or
hive; return by turtles after years to natal beach, or by salmon to natal stream). Much of the
information on how birds navigate has come from studying homing in domestic pigeons.
Why migrate?
animals that migrated must have left more offspring than if they had
not, so benefit must outweigh costs
Periodic migrations are often undertaken when population expands locally so
that animals
experience overcrowding, and can do better by moving elsewhere.
Seasonal migrations reflect the fact that the environment changes.
At its simplest, animals
move to track changes in the environment. Examples: Monarch butterflies migrate south for
winter warmth in Mexico; wildebeest follow the seasonal availability of water
Costs
Mortality risk - Huge losses of migrating animals due to
* exhaustion,
* predators,
* difficulty of finding food/water en route,
* collision with obstacles,
* storms etc.
Energetic costs: need to build up body fat before migrating.
Benefits
Energetic benefits
Reduction in competition
Reproductive benefits
Protection from predation by “swamping” predators
Energetic benefits
Migrate south in winter: avoid temperature stresses and associated
metabolic costs
Reduction in competition
Avoid competition for resources in tropical areas- move to
exploit fresh seasonally available foods in temperate zones
Reproductive benefits
Birds breeding in north: longer daylength for feeding and seasonal
high availability of food for young. Seek suitable breeding conditions/protection from
predators during breeding (grey whales in warm bays, seals and sea lions on traditional
beaches). In gray whales and salmon, migration both brings the sexes together (in warm
bays and streams, respectively) and provides a safe environment for young.
Protection from predation by “swamping” predators
in far north, short breeding season,
huge number of birds available at one time, probability of any one bird being taken is small.
Predators are then deprived of prey when birds leave breeding area, limiting population
expansion.
Types of orientation important in navigation and homing in animals
Pilotage, camass orientation, true navigation
Pilotage
steering a course using familiar landmarks
