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.

I. Migration Patterns
II. Evolution of Migration
III. Diversity of Migration
IV. Navigation in Migration

Primarily a non-tropical phenomenon (with some altitudinal migration seen in tropics).
Statistics of Migration in North America:
- 5 billion birds of 200 species migrate each year, often traveling to Central or South America.
- Over 80% of breeding bird species in the Canadian boreal region winter farther south, approximately 50% migrating to tropical or subtropical regions.
- 50% of wintering birds in Mexico are migrants; Panama sees 30-40% migrant birds, Ecuador: 10-25%.
Migration Cases:
- Shorebirds like the bar-tailed godwit can fly 80-90 hours nonstop, covering distances such as 11,000 km across the Pacific from Arctic to southern regions.
- Migrating birds often exhaust fat and water reserves during long, nonstop flights, comparable to humans sprinting for 80 hours.
- Birds aim to minimize energetic costs involved in migration.

Waterfowl (Ducks & Geese): Utilize specific, narrow, well-defined flyways; trackable via hunter bands.
- Significant for conservation initiatives.
Songbirds:
- Less information available on flyways.
- Tend to use weather fronts for navigation.
Boreal Bird Migration:
- An estimated 3-5 billion birds migrate from Canada's Boreal Forest to various regions in the Americas year-round.

Types of Migration:
- Partial migration: Some species may migrate over short distances.
- Split populations: Some species have migratory and resident populations.
Evolutionary Trajectory:
- Three basic stages observed in the evolutionary development of migration behaviors.
- Example: Fox sparrow exhibits both migrant and non-migrant populations.
- Hypotheses for Migration Evolution:
  1. Competition for Resources & Range Expansion: Movement originates from species’ adaptations during warm months to exploit available resources in warmer areas; subsequently migrating during winter months due to food shortage.
  2. Climate Change: Initial populations lived year-round in northern locales during warmer climates; adaptation forced seasonal southward migration as climate turned colder.
- Phylogenetic analysis indicates that many migrating species are originally tropical.

Ultimate vs. Proximate Explanations:
- Proximate: Triggered by day-length perception and hormonal changes.
- Ultimate: Focused on the functional and evolutionary history regarding fitness consequences of this behavior.

Considerations include risks of starvation, predation, delayed breeding seasons, and weather-related challenges.
Specific bird species like Eleonora’s Falcon prey on migrants, posing additional risks during migration.

Adaptation refers to inherited traits that confer reproductive advantages.
- Traits that evolve through natural selection must demonstrate a net benefit over costs.

Energetic advantages observed in V formations, which can reduce drag by up to 65%.
Quality of wintering habitats directly impacts survival rates and reproductive success.

Migration is not limited to birds alone; various animal species also exhibit migratory behaviors.
Caribou Migration:
- Regular migration patterns for 6 herds in western Canada, maximizing accessibility to abundant foraging opportunities and minimizing predator encounters.
- Seasonal ranges specific to the Central Arctic caribou herd cover extensive areas with rich grazing opportunities, particularly during summer calving periods.
- Caribou migration patterns are threatened by human activities, particularly mining operations and road construction in traditional migratory routes.

Genetic variations may influence migratory behaviors, demonstrated in a study with blackcap passerine birds exhibiting diverse migration routes based on population heritage.