Do birds start migrating in August?

Birds migrate at different times of the year depending on the species and their breeding and wintering grounds. However, late summer and early fall is when we start to see large numbers of birds migrating south for the winter. So when exactly do most birds start their migration journeys?

When migration starts

Most migratory birds begin migrating south between August and November. The timing depends on the species and age of the birds. Here’s an overview of when different types of birds head south for the winter:

• Shorebirds: These birds that live along the coast and wetlands start migrating as early as July. Examples are sandpipers, plovers, stilts.
• Songbirds: Most songbirds like warblers, thrushes, and vireos start migrating in August and September.
• Raptors: Birds of prey like hawks, eagles, and falcons migrate from August through November depending on the species.
• Waterfowl: Ducks, geese, and swans begin migrating starting in August through October.

So while a few early migrators like shorebirds may start their southern journeys as early as July, the peak migration time for most birds is late August through October. This coincides with the end of breeding season and chicks fledging, as well as decreasing daylight and food sources.

Why do birds migrate in the fall?

Birds primarily migrate to move between breeding grounds where they nest in the spring and summer, and non-breeding wintering grounds where they can find adequate food and shelter during the colder months. There are several triggers that spur birds to migrate in the fall:

• Decreasing daylight: As days get shorter in August and September, hormones in birds signal to start migrating.
• Lack of food: Insects, seeds, fruit, and other food sources decline as winter nears, so birds head south where food is more plentiful.
• Temperature changes: Cooler temperatures in northern climates encourage migration to warmer southern regions.
• Genetics: Migratory behavior is innate in many species and kicks in seasonally.

By migrating in the fall, birds can take advantage of favorable conditions and ample food on their wintering grounds farther south. Their seasonal migration is all about finding the best places to breed and overwinter.

How do birds know when to migrate?

Birds have an amazing internal clock and senses that tell them when it’s time to migrate. Here are some of the cues birds use:

• Changes in daylight: Birds sense decreasing day length in the fall which triggers hormonal changes for migration.
• Temperature and weather patterns: Cooler temperatures and storms make birds restless to move south.
• Food availability: Scarcer food and difficulty foraging motivates migration.
• Internal clock: Even when in captivity, birds become restless and active during their normal migration periods, indicating an innate biological clock.
• Fat stores: Birds’ bodies automatically build up fat reserves when it’s time to migrate.

Young birds on their first migration may follow cues from experienced adults who know the optimal departure and journey times. Birds are amazing navigators capable of exploiting multiple cues to determine when to head south each fall.

How long does fall migration take?

The length of fall migration for birds depends greatly on the distance between their breeding and wintering grounds. Here are some approximate migration durations for birds migrating from Canada and the northern United States:

• Short-distance migrants: 1-2 weeks. Birds like American robins and red-winged blackbirds that winter in the southern U.S. or Mexico.
• Medium-distance migrants: 4-6 weeks. Birds like barn swallows and bobolinks that travel to Central or northern South America.
• Long-distance migrants: 2 or more months. Shorebirds and some songbirds that journey all the way to southern South America.

Factors like weather, food availability, predators, and geographic barriers along the route also affect migration timing. While some birds make the trip south quite quickly, most species have a more prolonged autumn migration journey, stopping to rest and refuel along the way in suitable habitats.

Primary migration flyways in North America

There are four main flyways or migration routes that birds travel from their northern breeding areas to southern wintering grounds in North America:

• Atlantic Flyway – Along the Atlantic coastline
• Mississippi Flyway – Along the Mississippi River valley
• Central Flyway – Between the Rocky Mountains and Mississippi River
• Pacific Flyway – Along the Pacific Coast

Some birds follow these highways of stopover habitat very closely, while other species take more divergent paths to their destination. Here is a map of the primary migration flyways across North America:

These flyways funnel huge numbers of birds along similar routes twice per year during migration seasons. Ornithologists can use this behavior to study and monitor migratory bird populations.

How far do birds migrate?

Migration distances vary tremendously depending on the species of bird. Here are some examples of average one-way migration distances for birds that breed in the contiguous United States and Canada:

• Ruby-throated hummingbird: 2,000 miles from eastern Canada to Central America
• Barn swallow: 3,000 miles from Canada to South America
• Bobolink: 6,500 miles from Canada to southern South America
• Blackpoll warbler: 7,500 miles from Canada to northern South America
• Red knot: 9,300 miles from Arctic Canada to southern South America

That’s like flying the distance from New York to LA over and over again each year for many small songbirds! The arctic tern holds the record for the longest migration, flying over 30,000 miles round-trip between Arctic breeding grounds and Antarctic wintering areas.

Why do some birds migrate short distances while others travel thousands of miles?

The distance birds travel during migration depends largely on how far they need to go to find suitable habitat, food, and climate conditions in the winter. Species like American robins and dark-eyed juncos that breed in Canada can find adequate winter quarters in the southern U.S. or Mexico, so they migrate relatively short distances of a few hundred or thousand miles. On the other hand, birds that breed in the far north like bobolinks and semipalmated sandpipers require temperate and tropical regions farther south in Central and South America to spend the winter, so they migrate much farther – thousands of miles each way. Some key factors determining migration distance include:

• Breeding range: Birds that nest farther north generally migrate longer distances.
• Winter habitat needs: Birds requiring specific habitat types, foods, or climate conditions must migrate farther to reach those environments.
• Geography: Birds distribute across continents based on geographic barriers like mountains and oceans that affect migration distance.

In general, migratory songbirds breeding in the northern U.S. and Canada head to the southern U.S., Mexico, Central America or northern South America for winter. While birds that nest in the Arctic tundra and boreal forests of Canada have the longest migrations down to southern South America.

What are the longest mammal migrations?

While birds are famous for their epic migrations, some mammals also migrate long distances. Here are a few of the record holders for long-distance mammal migrations:

• Caribou: Grant’s caribou migrate up to 3,100 miles between Alaska and the Yukon Territory.
• Gray whale: Eastern Pacific gray whales migrate 5,000-7,000 miles between Arctic feeding grounds and Mexican breeding areas.
• Humpback whale: Some humpback whale populations migrate 3,000 miles or more between high latitude feeding grounds and tropical breeding areas.
• Arctic tern: The Arctic tern holds the record for the longest migration of any animal, flying over 30,000 miles annually between northern and southern polar regions.

While not often considered migrants, many species of bats including hoary bats and silver-haired bats migrate long distances between summer ranges and southern wintering grounds. Monarch butterflies are also famous migrants traveling up to 3,000 miles from the U.S. and Canada to overwinter in central Mexico.

What triggers spring migration?

Just as changing conditions in the fall spur southbound migration, birds use cues in the early spring to know when to start migrating north again. Here are some factors that trigger spring migration:

• Increasing daylight: Birds sense the growing day length as winter turns to spring.
• Warmer temperatures: Warming temperatures encourage birds to move northward again.
• Food availability: Insects, seeds, and vegetation become available providing food sources along the migration route.
• Hormones: Changes in hormones like corticosterone provide an internal signal to prepare for migration.
• Fattening: Birds start accumulating fat reserves to fuel northbound migration.

The lengthening daylight is often cited as the most important external cue for spring migration. The timing aims to arrive on the breeding grounds when conditions are best for nesting, pairing, and raising young.

How do birds navigate during migration?

Birds rely on a suite of amazing senses and abilities to navigate their biannual migration journeys. Here are some of the tools and strategies birds use to find their way:

• Compass senses: Birds can detect magnetic fields and orient themselves based on the sun’s position.
• Landmark recognition: Visual cues like mountain ranges, rivers, coastlines, and vegetation patterns guide birds.
• Celestial cues: Birds use stars for orientation at night.
• Smell-based navigation: Scents help birds recognize habitats and locate specific breeding/wintering sites.
• Time-based navigation: Birds use an internal clock and changing sunset/sunrise times to judge their latitude.
• Memory and spatial learning: Experience helps birds map out optimal routes and locate good stopover habitat year after year.

Young birds learn migration routes and skills from traveling with experienced adults. Different species also use specialized navigation adaptations; for example, bobolinks can sense very subtle variations in the Earth’s magnetic field.

Conclusion

While a few early migrators like shorebirds and juvenile hawks get a head start in July and August, most North American landbirds don’t begin migrating south until late August through September. Decreasing daylight, lack of food, cooling temperatures, and hormonal changes signal it’s time to move toward wintering grounds farther south. This 2 to 4 month autumn migration journey happens along established flyways and over distances ranging from a thousand to tens of thousands of miles depending on the species. An internal clock and various senses like the magnetic compass guide birds along sometimes incredibly lengthy seasonal migrations, one of nature’s most amazing phenomena.