Birds migrate at different times of the year depending on the species. However, late summer and early fall is a very common time for birds to migrate south for the winter. So for many bird species, the answer is yes, they do migrate south in August.
When do birds migrate?
There are a few key times of year when birds migrate:
- Spring migration – February to May. Birds fly north to their breeding grounds to nest and raise young.
- Fall migration – August to November. Birds return south to warmer climates where food is more plentiful in the winter.
Not all birds migrate. Some species like chickadees, titmice and woodpeckers stay put year-round. But many popular backyard birds like robins, hummingbirds, orioles, and swallows migrate long distances each year.
Fall migration tends to take place over a longer period of time than spring migration. This is because there is less urgency to reach the wintering grounds quickly. The timing of migration depends on the species, but here are some general patterns:
- Shorebirds are some of the earliest fall migrants, starting their southbound journey as early as July.
- Warblers, vireos, swallows, and flycatchers migrate in August and September.
- Sparrows and hawks peak in October and November.
- Ducks, geese and loons migrate from October through December.
So for many bird species, August is right in the heart of fall migration season as they travel south to their winter habitat.
Why do birds migrate in the fall?
Birds migrate south in the fall for a few key reasons:
- Food – Food becomes much more scarce as winter arrives. Insects die off, fruit is gone, seeds become covered in snow. Birds must fly south where they can find nourishment.
- Shelter – The bare trees and icy climates of northern winters provide little shelter. Birds migrate to warmer climates with leafy trees and vegetation for cover.
- Water – Ponds, lakes and rivers freeze over in the winter. Birds need liquid water to drink and bathe.
- Changing daylight – The shortening days of late summer trigger hormonal changes in birds that spur the urge to migrate south.
By migrating to warmer southern climates in the U.S., Mexico, Central and South America, birds have the food, shelter and water they need to survive the winter. Some birds like the Arctic tern even migrate all the way to Antarctica!
What birds migrate south in August?
Many familiar backyard birds migrate in August as fall migration kicks into high gear. Some examples include:
- Warblers – Common Yellowthroat, Yellow, Palm, Pine, Wilson’s
- Swallows – Tree, Barn, Bank, Cliff
- Tanagers – Summer, Scarlet
- Orioles – Baltimore, Orchard
- Terns – Least, Caspian, Common
- Flycatchers – Eastern Phoebe, Eastern Kingbird
- Vireos – Red-eyed, Philadelphia, Warbling
- Hummingbirds – Ruby-throated
- Cuckoos – Black-billed, Yellow-billed
This is just a sampling of some of the birds that head south each August. Even popular backyard birds like American Robins, Northern Cardinals, Blue Jays and Cedar Waxwings migrate from northern areas during this time. Basically any bird species that does not remain year-round in your area migrates south in the fall through August and beyond.
What triggers birds to migrate in the fall?
Birds migrate south in the fall primarily due to changes in day length. As days shorten after the summer solstice, the decrease in daylight triggers hormonal changes in birds that spur the urge to migrate.
These hormone shifts cause birds to start eating more to pack on fat reserves for the long flight. Their internal compass also orients them to migrate in a particular direction based on the season. Many birds use celestial cues from stars and the magnetic pull of the earth to navigate during migration.
In addition to day length, dropping temperatures, scarce food, and bad weather also provide cues to birds that it is time to head south. But even if weather is still pleasantly warm in August, the shortening days compel many species to migrate.
How do birds know when to migrate?
Birds primarily use the following cues to know when to migrate each year:
- Changes in day length – As days get shorter after the summer solstice, hormones spur fall migration.
- Internal circadian rhythms – An internal clock sets the timing of seasonal migration.
- Genetics – Migration timing is programmed genetically to coincide with resource availability.
- Weather and food supply – Cold snaps, scarce food, and storms provide additional signals to migrate.
- Celestial cues – The stars, sun position, and magnetic fields guide navigation during migration.
While weather and food supply provide supplementary hints, scientists believe day length is the primary trigger that causes birds to migrate each fall. Their internal circadian rhythms are set to respond to the shortening days by preparing for migration.
How do birds know where to migrate?
Birds rely on a combination of instincts and learned behaviors to determine where to migrate each season. Here are some of the ways birds navigate over vast distances:
- Instinct – Young birds on their first migration follow their genetic programming.
- Learned routes – Adults return to areas they’ve migrated to before.
- Celestial cues – Birds use the sun, stars, and magnetic fields for guidance.
- Visual landmarks – Rivers, mountains, coastlines help birds orient themselves.
- Smell – Birds may smell their way by detecting plant odors or pollution.
The ability to successfully migrate and navigate over thousands of miles to specific wintering grounds is an amazing feat. Scientists are still studying exactly how birds do it with such precision from year to year.
How far do birds migrate?
Different bird species migrate varying distances each year. Some examples include:
- Hummingbirds – Migrate up to 2,000 miles from the U.S. to Central America.
- Plovers – Migrate around 5,000 miles from the Arctic to southern South America.
- Swallows – Migrate between 5,000 to 6,800 miles from North America to South America.
- Hawks – Some hawks like the Swainson’s migrate 7,500 miles each fall.
- Terns – The Arctic Tern has the longest migration at over 40,000 miles annually between the Arctic and Antarctica.
Even small songbirds routinely make marathon migrations of a few thousand miles. Migration distances vary widely based on the bird species, their breeding and wintering grounds, and geographical obstacles like large bodies of water or mountains they need to fly around.
Why don’t all birds migrate?
Not all birds migrate because some are able to find enough food and survive the cold northern winters. Birds that do not migrate often have the following advantages:
- Adaptations to handle cold like thick feathers and high fat reserves.
- Ability to store food to eat all winter.
- Ability to switch their diet to eat available winter foods.
- Territory or food caching behaviors.
- Ability to find shelter in tree cavities or thick evergreen forests.
Examples of birds that do not migrate include chickadees, crows, titmice, woodpeckers, jays, owls, and grouse. Their adaptions allow them to tough out the harsh northern winters.
Other species like robins and bluebirds may only migrate partway south. They fly far enough to escape the worst of winter but not all the way to the tropics. This partial migration gives them flexibility to react to winter weather each year.
How do birds know where to stop during migration?
During migration, birds use the following cues to know when and where to stop along their journey:
- Fat reserves – Stop when energy is depleted to rest and feed.
- Familiar landmarks – Stop at rivers, mountains, or coastlines they recognize.
- Genetics – Follow ancestral routes imprinted in their DNA.
- Weather changes – Stop when they reach warmer southern climates.
- Food availability – Stop when they find plentiful food sources.
Younger birds follow the lead of adults who have made the migration before and know the routes and optimal stopping points. Birds carefully time their migration and stops to coincide with peak food availability along the way.
Why do some birds migrate at night?
Many birds migrate at night for the following reasons:
- Cooler night air makes flight more efficient.
- Less turbulence and air currents at night.
- Less risk of overheating during long flights.
- Less danger from hawk attacks compared to daytime.
- Can use stars and the magnetic field to orient themselves.
Night migration makes sense physiologically for many small birds. The still night air allows more ease of flight over long distances. Predators are less active at night as well. However some larger birds like hawks, geese and swans do migrate during the day.
Do birds migrate over water?
Many birds do successfully migrate over large expanses of water each year. Land birds like warblers and thrushes are even capable of making non-stop flights of 500 miles or more over open ocean.
Some examples of amazing ocean migrations include:
- Blackpoll warblers fly non-stop for up to 88 hours over 2000 miles of Atlantic Ocean to South America.
- Swainson’s hawks fly 1500 miles non-stop over the Gulf of Mexico.
- Songbirds use offshore wind patterns and islands to rest during Pacific and Atlantic crossings.
- Shorebirds fly vast distances over oceans between nesting areas in the Arctic to South America.
Wind patterns, positional stars for navigation, and large fat reserves help power birds on these incredible trans-oceanic migrations. However, bad weather like storms and strong headwinds can blow migrating birds far off course resulting in exhaustion and mortality.
Effects of climate change on migration
Climate change may be impacting birds’ seasonal migration in the following ways:
- Shifting migration timing as weather patterns change.
- Changes in migration routes and stopover sites.
- Worse impacts from storms if migration timing is mismatched.
- Increased risk of drought, heatwaves and extreme weather.
- Mismatch with peak food availability at destinations.
- Threats to habitats from rising sea levels.
Birds’ internal migration clocks are timed to the seasons and changing day length. As climate patterns shift, some birds are migrating at different times or forced to find new routes with altered habitat conditions.
More research is needed to fully understand the complex impacts of climate change on avian migration over the coming decades.
Protecting migratory birds
Here are some ways we can help protect migratory birds on their incredible seasonal journeys:
- Providing habitat corridors and stopover sites with native plants and food sources.
- Eliminating hazards like illuminated buildings or towers.
- Reducing use of pesticides that can poison birds.
- Keeping cats indoors so they don’t kill migrating songbirds.
- Supporting conservation of habitats on migration routes and wintering grounds.
- Following bird-friendly practices in forestry, agriculture, and wind power development.
You can also help track migratory birds by reporting marked birds or submitting observations to eBird. Improving scientific knowledge supports better policies to protect migrants on their full life cycle journey.
Conclusion
August sees the peak of fall migration for many bird species. Shortening daylight triggers hormonal changes that spur birds to head south to warmer wintering grounds. Amazing navigation abilities guide birds over thousands of miles, including risky ocean crossings and through bad weather. Supporting migratory bird habitat and conservation is vital as climate change alters migration patterns. The astonishing marathon flights made by birds each year are crucial to their survival and a wonder of the natural world.
