Migration:

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Migration

• Overview
• Case Histories
• Mechanisms

15 November 2009
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Definition

• The movement of animals from one place to another
  
• occurs regularly
• usual seasonal
• round-trip
• example Pacific Brandt migratory route

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Migration known from all classes of vertebrates
and some insects

• Fish salmon, eels
• Reptiles sea turtles
• Mammals gray whale, African hoofed animals
• Birds widespread
• Amphibians California newt
• Insects butterflies, bees, beetles

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Non-migratory geographical movements

• Emigration, immigration
• Irregular movements irruptions
• Wandering nomadism
• Dispersal

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Techniques for Studying Migration

• Direct Observation
• Visual
• Sound
• Preserved Specimens
• Marking
• Bands
• Radio Tracking
• Satellite Tracking
• Radar Observation
• Laboratory
• Orientation and Navigation
• Physiology of Migration

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Migratory Patterns Birds

• Flyways and Corridors
• Patterns of Migration
• Latitudinal migration breed at one latitude,
  winter in latitude with milder climate
• Long-distance migration
• Arctic terns breed in Arctic, winter in
  Antarctic.  Can feed during migration.
• Many shorebirds (e.g. bristle-thighed curlew)
  breed in Arctic, winter in Polynesia. 10-15
  thousand km over water where can not stop to
  rest, feed
• Northern Wheatears (a thrush relative) breed in
  Greenland, migrate 2-3 thousand km over water to
  winter in Europe
• eastern US many birds migrate over the Atlantic
  Gulf of Mexico.  Use favorable winds.
• altitudinal migration
• some finches breed at higher elevation, migrate
  to lower elevation in winter
• blue grouse breed at medium elevation, migrate to
  higher elevation in winter
• partial migration some individuals migrate,
  others do not (ex some raptors, goldfinches)
• differential migration all individuals migrate,
  but some age /or sex classes migrate farther
  than others (ex dark-eyed juncos, American
  kestrels)

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Latitudinal migration

• Arctic tern (Sterna
• breed in Arctic
• winter in Antarctic
• 11,000 m. 1-way. 
• Can feed during migration.

USGS NPWRC Arctic tern
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Other latitudinal migrants

• Many shorebirds (e.g. bristle-thighed curlew)
• breed in western Alaska
• Fall migration over Pacific to Polynesia.
• 10-15 thousand km over water
• can not stop to rest, feed
• Lifespan to 23 years
• Short-tailed shearwater
• Neotropical migrants, e.g. tanagers, thrushes,
  warblers
• migrate over the Atlantic Gulf of Mexico.  Fly
  at night, use favorable winds, do not feed

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Elevational migrants

• some finches breed at higher elevation, migrate
  to lower elevation in winter, e.g. gray-crowned
  rosy finch
• blue grouse breed at medium elevation, migrate to
  higher elevation in winter

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Other classifications

• partial migration some individuals migrate,
  others do not
• Fox sparrow
• some raptors
• goldfinches
• differential migration all individuals migrate,
  but some age /or sex classes migrate farther
  than others
• dark-eyed juncos
• American kestrels

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Migratory Patterns Green turtle (Chelonia mydas)

• Physical separation of feeding and breeding areas
• Feed in marine pastures in quiet, low-energy
  areas
• Nest on high energy beaches

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Migratory Pattern Gray Whale(Eschrichtius
robustus)
14,000 miles round trip
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Why migrate?

• A way to use habitats or resources that are only
  available seasonally
• Food
• Breeding areas
• Retreats from high predation

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How did migration evolve?

• Benefits must outweigh costs.
• Three-step process, starting with nonmigratory
  population
• Environmental or ecological pressure
• change in local climate creates more pronounced
  seasons, thereby affecting food supply).
• Forces part of population to move to adjacent
  regions for part of year
• these adjacent regions must have better food
  supply
• Population moves back into ancestral region for
  breeding or wintering
• This creates a partially migratory population,
  and those with higher reproductive success will
  make it over those with lower reproductive
  success.

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Resources

• Weidensaul, Scott. 2000. Living on the Wind
  Across the hemisphere with migratory birds.
  North Point Press
• U.S. Fish and Wildlife Service