The Riddle The Riddle of Bird of Bird

MigrationMigration

Definition: periodic Definition: periodic mass movement of all or mass movement of all or part of population from part of population from one area to another and one area to another and then backthen backSome other types of Some other types of Movements Movements

NomadismNomadismPost-natal dispersalPost-natal dispersal

Wanderings for Wanderings for unoccupied home unoccupied home ranges or territories to ranges or territories to claimclaim

IrruptionsIrruptions (e.g., Snowy (e.g., Snowy OwlOwlAggregations at Aggregations at superabundant food superabundant food sourcesource

Why Why Migrate?Migrate?

• Migration as Migration as OpportunityOpportunity– NestingNesting– FoodFood

• Migration as Migration as EscapeEscape– From From

weatherweather– From lack of From lack of

foodfood

What are the Benefits of What are the Benefits of Migration?Migration?• Avoid harsh and dangerous Avoid harsh and dangerous

winter climateswinter climates• Avoid lack of food during Avoid lack of food during

winter winter – Especially insectivorous Especially insectivorous

birds such as wood warblersbirds such as wood warblers– Especially fruit-eating birds Especially fruit-eating birds

such as waxwingssuch as waxwings• Avoid lack of cover during Avoid lack of cover during

winterwinter• Migrate from area of sparse Migrate from area of sparse

or no food to area of or no food to area of relatively abundant foodrelatively abundant food

• So migration enhances So migration enhances survivorship of many survivorship of many populationspopulations

What are the Costs of What are the Costs of Migration?Migration?• The Price of Migration The Price of Migration

– Migration Risks Migration Risks

• 100 million NA waterfowl migrate 100 million NA waterfowl migrate in fall, 40 million return in springin fall, 40 million return in spring

• Risks attend all long distance Risks attend all long distance migrationsmigrations

– Exposure to predatorsExposure to predators– Exposure to exhaustionExposure to exhaustion– Exposure to harsh, dangerous Exposure to harsh, dangerous

weather conditions during weather conditions during middle of migrationmiddle of migration

• Storms, contrary winds blow Storms, contrary winds blow many species off coursemany species off course

• Especially risky for over water or Especially risky for over water or over desert migrantsover desert migrants

• Eleonora’s Falcon breeds on Eleonora’s Falcon breeds on Mediterranean areas in fall to take Mediterranean areas in fall to take advantage of migrants.advantage of migrants.

What are the Types What are the Types of Migration?of Migration?• Seasonal North/SouthSeasonal North/South

– Primary patternPrimary pattern– Except that in southern Except that in southern

hemisphere migration hemisphere migration occurs as a South/North occurs as a South/North movementmovement

• Elevational MigrationsElevational Migrations– Summer/winter shift Summer/winter shift

from high elevations to from high elevations to low elevationslow elevations

• LatitudinalLatitudinal– Movement from interior Movement from interior

areas to shore areasareas to shore areas

Everyone Everyone doesn’t doesn’t Migrate: Migrate: AlternativesAlternatives

• Enter dormancy Enter dormancy or torporor torpor

• Remain on Remain on territory territory throughout the throughout the yearyear– Thereby first Thereby first

in spring to in spring to claim mateclaim mate

How did migration How did migration evolve?evolve?• Still Highly ConjecturalStill Highly Conjectural• Northern Birds South: Ice Age TheoryNorthern Birds South: Ice Age Theory

– 100,000 years plus of Ice Ages 100,000 years plus of Ice Ages – Separated by Interglacial PeriodsSeparated by Interglacial Periods– Northern Birds displaced southward with each new ice Northern Birds displaced southward with each new ice

age, northward with deglaciation age, northward with deglaciation

• Tropical Birds North Tropical Birds North – Open, empty habitats (competition-free habitats)Open, empty habitats (competition-free habitats)– Hummingbirds, flycatchers, wood warblers are all Hummingbirds, flycatchers, wood warblers are all

moving northwardsmoving northwards

• Gradualism: Generational North with the spring Gradualism: Generational North with the spring

Migration Evolution as a balance Migration Evolution as a balance between Advantages/Disadvantages---between Advantages/Disadvantages---SurvivorshipSurvivorship

Is Migration is Evolving Now?Is Migration is Evolving Now?

European Robins and Ringed European Robins and Ringed PloverPlover Partial Migration of population Partial Migration of population

(some subpopulations remain (some subpopulations remain throughout yearthroughout year

Others migrate every year Others migrate every year Still others migrate or don’t Still others migrate or don’t

migratemigrateRemain on territory during Remain on territory during

mild wintersmild wintersMigrate during harsh Migrate during harsh

winterswintersCalled Called Behavioral Behavioral

PolymorphismPolymorphism (i.e., the (i.e., the population is polymorphic population is polymorphic with respect to behavior with respect to behavior

How do How do Birds Birds Prepare Prepare for for Migration?Migration?• MoltingMolting

– Postnuptual Postnuptual moltmolt

– New feather New feather growth needed growth needed for long for long migratory migratory flightsflights

• Migratory Migratory restlessnessrestlessness– TermedTermedZugunruheZugunruhe

• Putting on weightPutting on weight

Migration FatMigration Fat

• Fat yields 2x energyFat yields 2x energy• Birds add to 20% body Birds add to 20% body

mass, mostly in fatmass, mostly in fat• Fat deposits in adipose Fat deposits in adipose

tissue of skin, in tissue of skin, in muscles, organsmuscles, organs

• Spreads as a thin layer Spreads as a thin layer just under skinjust under skin

• Also provides Also provides insulation during high insulation during high altitude migration altitude migration flightsflights

Some Patterns of Migration ISome Patterns of Migration I

• Red PhalaropeRed Phalarope

• Nests in tundraNests in tundra

• Winters at SeaWinters at Sea

Self Study Topics for Self Study Topics for MigrationMigration

• Use the internet to find information Use the internet to find information sites about bird migrationsites about bird migration

• Select your favorite bird and review Select your favorite bird and review its migration patterns with respect to:its migration patterns with respect to:– How far does it migrate?How far does it migrate?– What route does it take to migrate?What route does it take to migrate?– What factors influence its migration?What factors influence its migration?– How does it navigate (find its way) How does it navigate (find its way)

during migration?during migration?