birdmigration.ppt
- 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?