Many species of birds migrate south in the winter months to escape the cold weather and find more abundant food sources. Bird migration is an amazing feat of endurance, navigation, and survival. Some birds fly enormous distances, while others may only migrate short distances. The exact timing and routes taken by migratory birds depend on the species, weather, food availability, and other factors. While migration may seem mysterious, scientists have uncovered fascinating details about the biology and behavior behind these seasonal journeys. This article explores what types of birds migrate and their incredible migratory abilities.
What is bird migration?
Bird migration refers to the seasonal travel of bird populations between breeding and wintering grounds. It involves long-distance, usually north-south, journeys that are undertaken by hundreds of bird species. The main driver of migration is the search for resources. Birds migrate to take advantage of abundant food, nesting locations, and favorable weather conditions. By moving with the seasons, migratory birds can breed in summer and escape harsh winters.
Migration allows birds to make use of seasonal food sources, breed in ideal habitats, and avoid extreme weather and predators. However, it requires extensive energy reserves and complex navigational skills. Migrating birds undergo physiological changes to prepare for strenuous flights and use the earth’s magnetic fields, stars, landmarks, and odor cues to find their way.
Why do birds migrate?
Birds migrate for several key reasons:
- Food availability – Birds migrate to regions where food sources are more plentiful in different seasons.
- Breeding habitat – Migration allows birds to nest and raise young in optimal summer environments.
- Weather – Birds escape harsh winter conditions by moving to warmer regions.
- Predation avoidance – Migration reduces pressure from predators in seasonal habitats.
- Seasonal resources – Birds follow seasonal food sources, such as insect hatches or fruiting plants.
By moving with the changing seasons, migratory birds can take advantage of abundant resources during summer breeding and survive through scarce winter conditions.
How far do birds migrate?
Migration distances vary widely among species, from just a few kilometers to transcontinental journeys:
- Short-distance migrants – Move less than 500 km between breeding and wintering grounds. Example: American goldfinch
- Medium-distance migrants – Travel 500 – 5000 km between seasonal ranges. Example: Ruby-throated hummingbird
- Long-distance migrants – Makemigrations longer than 5000 km each way. Example: Arctic tern
The Arctic tern holds the record for the longest migration, flying over 70,000 km annually between Arctic breeding areas and Antarctic wintering grounds. Small songbirds may only migrate a few hundred kilometers between forests. Larger birds like geese and hawks can fly thousands of kilometers seasonally.
Major flyways used by migrating birds
Migratory birds travel along established routes called flyways. There are four major flyways over North America:
- Atlantic Flyway – Along eastern North America
- Mississippi Flyway – Follows the Mississippi River valley
- Central Flyway – Between the Rocky Mountains and Mississippi River
- Pacific Flyway – Along western North America
Some birds follow these flyways very closely, while other species have more variable migration paths. Flyways include important stopover sites where birds rest and refuel during journeys. They concentrate food resources and safe habitat for migrating birds.
Atlantic Flyway
The Atlantic Flyway follows the Atlantic coastline from Florida and the Gulf of Mexico to eastern Canada and the Arctic. Key stopovers are along large bays and peninsulas on the Atlantic coast. Many neotropical migrants such as warblers, vireos, and tanagers use this flyway.
Mississippi Flyway
The Mississippi Flyway corresponds to the Mississippi River valley and its major tributaries, stretching from the Gulf of Mexico to Canada. This inland route concentrates birds along forested river ecosystems. Waterfowl such as ducks and geese heavily use this flyway.
Central Flyway
The Central Flyway covers the Great Plains from Texas to the Prairie Provinces of Canada. Birds follow this broad front through the continent’s interior. Shorebirds and birds of prey rely on this flyway.
Pacific Flyway
The Pacific Flyway includes the western coastline from Mexico to Alaska. Birds follow the Cascades and Sierra Nevada mountain ranges. Water birds like geese and cranes commonly use this coastal route.
What types of birds migrate?
Many diverse bird groups migrate, while some species remain in the same regions year-round:
- Waterfowl – Ducks, geese, and swans undertake long migrations, including Arctic geese that travel from Mexico to the Arctic.
- Shorebirds – Most shorebirds, like plovers and sandpipers, migrate long distances along coasts and interior wetlands.
- Birds of prey – Hawks, eagles, and falcons soar along flyways during seasonal movements.
- Warblers – Small songbirds like warblers perform amazing migrations over thousands of kilometers.
- Thrushes – Thrushes and robins traverse North America during spring and fall flights.
- Sparrows – Many sparrow species migrate, while some temperate sparrows are year-round residents.
- Blackbirds – Grackles, blackbirds, and orioles migrate in large mixed flocks.
- Hummingbirds – Tiny hummingbirds make the long journey between Mexico and northern nesting grounds.
In addition to these common migrants, most North American swallows, vireos, tanagers, and flycatchers head south each fall. However, some species like chickadees, nuthatches, and woodpeckers remain through winter in most regions. Migration strategies vary widely depending on the bird’s habitat needs and ability to withstand cold temperatures and snow cover.
Long-distance migration champions
Some birds stand out for their seemingly impossible migratory feats. Here are some of the top long-distance migration champions among North American birds:
Arctic Tern
Arctic terns breed in the far north of North America and Eurasia. They migrate all the way to the Antarctic coasts and pack on so much mileage that they experience two summers per year. Their total migration can exceed 90,000 km roundtrip.
Bar-tailed Godwit
This large shorebird holds the record for nonstop migration, flying 11,000 km from Alaska to New Zealand without breaking its journey. Godwits make this journey in about nine days.
Ruby-throated Hummingbird
Tiny hummingbirds migrate enormous distances relative to their size. Ruby-throats fly nonstop across the Gulf of Mexico and travel up to 4,000 km between Central America and Canada.
Blackpoll Warbler
Blackpoll warblers display amazing endurance for a 12-18 gram bird. They depart the northeastern U.S. and fly nonstop over the Atlantic Ocean to winter in northern South America.
Species | Total Migration (km) | Notes |
---|---|---|
Arctic Tern | 90,000 | Roundtrip from Arctic to Antarctica |
Bar-tailed Godwit | 11,000 | Nonstop from Alaska to New Zealand |
Ruby-throated Hummingbird | 4,000 | Long migration relative to tiny size |
Blackpoll Warbler | 4,000 | Nonstop transatlantic flight |
How do birds navigate migration?
One of the most intriguing aspects of bird migration is how birds manage to navigate over such enormous distances between seasonal habitats. Scientists have revealed several key tools birds use to find their way during migration:
Sun compass
Birds determine direction using the sun’s position. Even on cloudy days, they can sense polarized light patterns for orientation.
Stars
On clear nights, birds use stars to orient themselves. The band of the Milky Way likely serves as a prominent guide.
Earth’s magnetic field
Birds contain deposits of magnetite in their beaks and brains. They use the planet’s magnetic fields like a compass to determine direction.
Landscape cues
Birds rely on landscape features like coastlines, mountains, rivers, and vegetation patterns to navigate along established routes.
Smell-based maps
Scientists think birds may create “odor maps” by linking smells and chemical cues with locations along migration routes.
Despite their small size, birds navigate with amazing skill over incredible distances. Their navigational tools include a variety of senses fine-tuned to cues from the sun, stars, earth, and environment.
How do birds prepare for migration?
To fuel their strenuous journeys, birds undergo dramatic physiological transformations:
- Hyperphagia – Birds nearly double their body mass by building fat stores. Fat provides energy for distance flights.
- Atrophy – Birds reduce the size of organs not needed for migration, like digestive organs.
- Muscle changes – Birds convert muscle to fat and increase breast muscle size for powering flight.
- Hormone changes – Hormones like corticosterone prepare the bird’s body for migratory activity.
These changes allow birds to take off with enough fat stores to fly hundreds or thousands of kilometers. Some shorebirds will even double their body weight before a nonstop transoceanic flight.
Threats faced by migratory birds
Although migration helps birds locate optimal habitats, it also exposes them to numerous threats along their flyways:
- Habitat loss – Loss of wetlands and stopover sites reduces food resources and refuge.
- Buildings and towers – Birds collide with structures during travel, especially at night.
- Wind turbines – Wind farms pose a collision risk, especially for raptors and waterfowl.
- Overhunting – Some regions still permit excessive hunting of migratory waterfowl and shorebirds.
- Pesticides – Contaminants accumulate in birds and reduce migration success and reproduction.
- Invasive species – Introduced species like house cats and rats threaten migrating birds.
- Climate change – Shifting habitat conditions could disrupt delicate migration timing.
Protecting migration stopover habitats and mitigating human infrastructure threats are key steps to bolstering the resilience of migratory birds.
How can you observe migration?
Anyone can witness the wonder of migration by observing the changing bird populations in their area:
- Use apps like eBird to record arrival and departure dates of migratory species.
- Visit wetland refuges along major flyways to see concentrations of migrating waterfowl.
- Look for southbound flocks of birds like swallows, blackbirds, and hawks in fall.
- Listen for the arrival of neotropical songbirds like warblers and vireos in spring.
- Track the shifting populations of wintering backyard birds through seasonal feeders.
Local Audubon chapters, bird observatories, and park programs also offer guided opportunities to spot migrations. Simply going outside during migration seasons allows you to witness some of the epic seasonal journeys undertaken by birds.
Conclusion
Bird migration is an endlessly fascinating phenomenon. From Arctic terns circumnavigating the globe to tiny hummingbirds crossing the Gulf of Mexico, migratory birds demonstrate incredible feats of endurance and navigation. Their seasonal movements highlight the interconnectedness of ecosystems across continents. Conservation of migratory birds requires protecting habitats along their flyways from pole to pole. As changing conditions threaten migration patterns worldwide, maintaining healthy ecosystems and migration stopover sites will be key to sustaining these epic seasonal bird journeys.