The Riddle of Bird Migration

1. 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

2. Why Migrate? • Migration as Opportunity • Nesting • Food • Migration as Escape • From weather • From lack of food

3. What are the Benefits of Migration? • Avoid harsh and dangerous winter climates • 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 • Migrate from area of sparse or no food to area of relatively abundant food • So migration enhances survivorship of many populations

4. What are the Costs of Migration? • The Price of Migration • Migration Risks • 100 million NA waterfowl migrate in fall, 40 million return in spring • 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 • Especially risky for over water or over desert migrants • Eleonora’s Falcon breeds on Mediterranean areas in fall to take advantage of migrants.

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

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

7. How did migration evolve? • Still Highly Conjectural • 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 • Open, empty habitats (competition-free habitats) • Hummingbirds, flycatchers, wood warblers are all moving northwards • Gradualism: Generational North with the spring

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

9. 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

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

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

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

13. Self Study Topics for Migration • Use the internet to find information sites about bird migration • 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?