migration
Boreal Ecology Today: Migration
Reference: Egevang et al. 2010. Tracking of Arctic terns Sterna paradisaea reveals longest animal migration. Proceedings of the National Academy of Sciences 107:2078-2081.
Course Schedule
5-Feb: Migration
10-Feb: Patterns of species diversity
12-Feb: Plant-animal interactions
17-Feb: Mid-term break
19-Feb: Mid-term break
24-Feb: Food web dynamics
26-Feb: Population cycles
3-Mar: Population cycles part 2
5-Mar: Ecosystem engineering
10-Mar: Wolf dynamics (guest lecture)
12-Mar: Exam 2 Schedule
Concepts in Migration
Migration vs. Dispersal
Migration: Often suggested as an adaptation to cold environments.
Dispersal: The movement of individuals away from their birth site or population.
North America's Boreal Forest
Significance: Home to the world's last great migrations.
Organizations: International Boreal Conservation Campaign, October 2008.
Notable Species:
Salmon
Whooping crane
Caribou
White-winged scoter
Palm warbler
Migration Patterns
I. Migration Patterns
Primarily a non-tropical phenomenon with exceptions for altitudinal migration in the tropics.
Approximately 5 billion birds of 200 species migrate each year in North America, often to Central or South America.
Breeding Patterns:
Over 80% of all bird species breeding in the boreal region of Canada winter farther south.
About 50% migrate to tropical or subtropical regions.
Winter in Mexico consists of 50% migratory birds.
Panama: 30-40%
Ecuador: 10-25%
II. Flight Durations and Energetics
Many shorebirds undertake significant non-stop flights.
Example: The bar-tailed godwit flies 11,000 km across the Pacific from the Arctic to the south.
Long non-stop flights drain all fat and water reserves, equating to human sprinting for 80 hours nonstop.
Birds employ strategies to minimize energetic costs associated with migration.
III. Migration Routes
Ducks & Geese: Utilize specific, narrow, and well-defined flyways.
Useful Conservation Insight: Observations of migration patterns provide conservation information.
IV. Shorebirds and Songbirds
Knowledge about songbird flyways is less robust.
Some species appear to utilize weather fronts for navigation.
Boreal Bird Migration
3-5 Billion birds migrate from Canada’s Boreal Forest to the Americas per year.
Maps show migration routes across North America including Western, Central, and Eastern Flyways.
Stable Isotope Analysis
Deuterium in feathers: Reflects rainfall in regions where feathers were grown.
Researchers use this data to trace migration routes based on feather analysis.
Stable Isotope Relationship: ratios can indicate origin and migration patterns.
Major Patterns of Migration
Soaring Birds:
Eagles and hawks predominantly use updrafts and thermals.
They fly during the daytime, requiring land proximity.
Flapping Birds:
Songbirds often fly over oceans to avoid turbulence and reduce energy expenditure.
Many migrate during the night, helping them avoid predators and enabling feeding opportunities during the day.
Night Flying Benefits
Helps avoid predators and enables feeding during the day.
Reduced turbulence because of minimized thermal activity at night.
Cooler night temperatures help prevent overheating of flight muscles.
Higher humidity during the night results in lower moisture loss for the birds.
Arctic Tern Migration
Distance: Arctic terns migrate over 19,000 km each way—total distance covers 70,900 km annually, potentially exceeding 2.4 million km over a lifespan of approximately 34 years.
Transportation Mechanisms:
Utilization of archival loggers to track their movements.
Must operate loggers below 5% of the bird's body mass.
Geolocators vs. Satellite Locators
Geolocators:
Smaller in size, more affordable, but data must be retrieved as they cannot transmit.
Accuracy within 185 km.
Satellite Tags:
Provide real-time data but can be heavier and more expensive.
Population Dynamics and Migration Timing
Spring: Northbound migration occurs faster (averaged 40 days).
Autumn: Southbound migration is longer and less direct (averaged 93 days).
Birds generally pause in areas of high marine productivity, using chlorophyll satellite data to identify stops during migration.
Evolution of Migration
Initial Evolutionary Stages
Partial Migration: Some species migrate over short ranges.
Split Populations: Some individuals become migratory while others become resident.
Exclusive Migration: Only migratory populations remain as resident populations gradually disappear.
Hypotheses on Migration Evolution
Resource Competition: Migration started as a response to dwindling resources in original habitats.
Species may have found new advantageous regions during warmer months, with migrations occurring during colder seasons.
Climate Change: Shifts in climate pushed species towards migratory behaviors as winters became too harsh.
Most migrating species are phylogenetically tropical in origin.
Understanding Migration Cues
Proximate vs. Ultimate Explanations
Proximate: Relates to immediate physiological triggers (e.g., hormonal changes due to day length).
Ultimate: Pertains to evolutionary advantages and fitness benefits of migration.
Adaptation and Selecting Traits
Adaptation Benefits: Traits must confer reproductive advantages—defined by costs and benefits assessments.
Cost/Benefit Analysis: If benefits outnumber costs, traits are selected for evolutionary progress.
Migration Costs and Benefits
Energetics: V formation can decrease drag by up to 65%.
Starvation Risks:
Strategies vary between becoming fat before long flights or taking shorter flights with feeding stops.
Predation Risks: Migrants face additional dangers such as predation from species like Eleonora’s Falcon and delayed breeding seasons due to migration timing.
Weather Risks: Environmental conditions can lead to misdirection or loss during migration.
Survival and Breeding in the North
Benefits include abundance of resources, long daylight hours, and reduced competition and predation risks.
Research by McKinnon et al. (2010) shows a latitudinal decrease in predation for migratory shorebirds, evidenced by nesting success in artificial nest studies.
Migration Diversity Beyond Birds
Migratory behaviors observed in various species, including caribou, cetaceans, and fish species such as salmon.
Migratory patterns are influenced by resource availability and habitat conditions that favor breeding and survival.
Example of Migratory Caribou
Herbivore Migration Strategy:
Maximize quality forage while minimizing predation and insect interactions, with regular calving grounds.
Seasonal migration patterns help ensure feeding and reduce blood loss during high foraging periods.
Fish Migration Types
Anadromous Lifecycle: Born in freshwater, migrate to the ocean, then return to spawn. Represent 2.5% of all fish species.
Example: Salmon lifecycle stages
Spawning occurs, adults die within 2 weeks post spawning.
Migrations see adults spending 1-8 years at sea before returning for reproduction.
Pacific salmon migrations include notable species like Chinook, Chum, Sockeye, Pink, and Coho salmon.
Insect Migration: Monarch Butterflies
Longest Migration: Traveling to Mexico, monarchs breed en route but reproduce only during their journey to summer habitats; they can migrate up to 8,000 km/year.
Migration Navigation
Key Cues
Visual Landmarks, Solar Compass, Stellar Compass, Geomagnetism, Olfaction:
Birds use various innate mechanisms to navigate accurately during migration.
Studies indicate migratory behavior differences in populations showcase genetic variances influencing migratory decisions (e.g., blackcaps behavior).
Impacts of Genetic Variation on Migration
Behavioral Differences: Genetic traits have led to distinct migratory patterns observed in Swabian blackcaps which exhibit two different migration paths.
Next Steps in Learning
Prepare for the next class on species diversity patterns, reading Mittelbach et al. 2007. Evolution and the latitudinal diversity gradient: speciation, extinction, and biogeography. Ecology Letters 10: 315-331.