The Riddle of Bird Migration  Definition: periodic mass movement of all or part of population from one area to another and then back  Some other types of Movements  Nomadism Post-natal dispersal  Wanderings for unoccupied home ranges or territories to claim  Irruptions (e.g., Snowy Owl  Aggregations at superabundant food source

Why Migrate? Migration as Opportunity Migration as Opportunity –Nesting –Food Migration as Escape Migration as Escape –From weather –From lack of food

What are the Benefits of Migration? Avoid harsh and dangerous winter climates Avoid harsh and dangerous winter climates Avoid lack of food during winter Avoid lack of food during winter –Especially insectivorous birds such as wood warblers –Especially fruit-eating birds such as waxwings Avoid lack of cover during winter Avoid lack of cover during winter Migrate from area of sparse or no food to area of relatively abundant food Migrate from area of sparse or no food to area of relatively abundant food So migration enhances survivorship of many populations So migration enhances survivorship of many populations

What are the Costs of Migration? The Price of Migration The Price of Migration –Migration Risks 100 million NA waterfowl migrate in fall, 40 million return in spring 100 million NA waterfowl migrate in fall, 40 million return in spring Risks attend all long distance migrations Risks attend all long distance migrations –Exposure to predators –Exposure to exhaustion –Exposure to harsh, dangerous weather conditions during middle of migration Storms, contrary winds blow many species off course Storms, contrary winds blow many species off course Especially risky for over water or over desert migrants Especially risky for over water or over desert migrants Eleonora’s Falcon breeds on Mediterranean areas in fall to take advantage of migrants. Eleonora’s Falcon breeds on Mediterranean areas in fall to take advantage of migrants.

What are the Types of Migration? Seasonal North/South Seasonal North/South –Primary pattern –Except that in southern hemisphere migration occurs as a South/North movement Elevational Migrations Elevational Migrations –Summer/winter shift from high elevations to low elevations Latitudinal Latitudinal –Movement from interior areas to shore areas

Everyone doesn’t Migrate: Alternatives Enter dormancy or torpor Enter dormancy or torpor Remain on territory throughout the year Remain on territory throughout the year –Thereby first in spring to claim mate

How did migration evolve? Still Highly Conjectural Still Highly Conjectural Northern Birds South: Ice Age Theory Northern Birds South: Ice Age Theory –100,000 years plus of Ice Ages –Separated by Interglacial Periods –Northern Birds displaced southward with each new ice age, northward with deglaciation Tropical Birds North Tropical Birds North –Open, empty habitats (competition-free habitats) –Hummingbirds, flycatchers, wood warblers are all moving northwards Gradualism: Generational North with the spring Gradualism: Generational North with the spring

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

Is Migration is Evolving Now?  European Robins and Ringed Plover  Partial Migration of population (some subpopulations remain throughout year  Others migrate every year  Still others migrate or don’t migrate  Remain on territory during mild winters  Migrate during harsh winters  Called Behavioral Polymorphism (i.e., the population is polymorphic with respect to behavior

How do Birds Prepare for Migration? Molting Molting –Postnuptual molt –New feather growth needed for long migratory flights Migratory restlessness Migratory restlessness –Termed Zugunruhe Putting on weight Putting on weight

Migration Fat Fat yields 2x energy Fat yields 2x energy Birds add to 20% body mass, mostly in fat Birds add to 20% body mass, mostly in fat Fat deposits in adipose tissue of skin, in muscles, organs Fat deposits in adipose tissue of skin, in muscles, organs Spreads as a thin layer just under skin Spreads as a thin layer just under skin Also provides insulation during high altitude migration flights Also provides insulation during high altitude migration flights

Some Patterns of Migration I Red Phalarope Red Phalarope Nests in tundra Nests in tundra Winters at Sea Winters at Sea

Self Study Topics for Migration Use the internet to find information sites about bird migration Use the internet to find information sites about bird migration Select your favorite bird and review its migration patterns with respect to: Select your favorite bird and review its migration patterns with respect to: –How far does it migrate? –What route does it take to migrate? –What factors influence its migration? –How does it navigate (find its way) during migration?