Seeing huge flocks of birds passing overhead during spring and fall migration is magical. Both suburban and urban birders look forward to seasonal migration periods to observe the spectacle of birds rarely seen. However, bird migration can often seem like a great mystery, with so many questions about why and how birds migrate, where they go, and how they get there.
Bird migration is the seasonal movement of birds between breeding and wintering grounds. Birds migrate to areas with better food, habitat, weather, and more daylight to ensure survival of offspring. They navigate via celestial cues, the earth’s magnetic field, mental maps, and other sensory inputs.
This article will provide you with an overview of bird migration fundamentals, and answer the questions that most people have about bird migration.
1. Birds Migrate to Ensure Survival of Themselves and Their Offspring
Why do birds migrate?
Birds migrate for numerous reasons including seeking better food resources, more daylight, superior nesting sites, fewer predators and parasites, and a more temperate climate. The primary motivation is the survival of birds and their future offspring, which depends on finding the best habitat to breed and raise their young.
Why and when do birds migrate north?
In the northern hemisphere, during spring migration, migrating birds will fly north since that’s where the food is, both for themselves and their young – plants are growing, yummy insects are plentiful, and excellent nesting sites are numerous. In addition, as the days become longer in the north, birds have more daylight hours to feed their chicks.
Yes, there is food in their current southern locations but there are also more predators in these areas, as well as more parasites and diseases that can quickly wipe out huge bird populations. So migrating birds fly north, both to flee danger and to seek better habitats and food sources.
Why and when do birds migrate south?
When the weather turns cold in the north, days become shorter, and there are fewer insects and plants, migrating birds will return south to their tropical homes.
Here is an inspiring and beautiful video of people flying along with migrating birds. The next time I travel to France, I am definitely doing this!
It is widely accepted that there are over 4,000 species of birds that migrate. This is about 40% of all bird species worldwide. In North America alone, about 75% of birds migrate.
2. Environmental Cues and Hormones Trigger Migration
How do birds know when to migrate? What triggers bird migration?
Birds know when it is time to migrate based on changes in their environment and hormones. Birds have an internal biological clock that primarily responds to days becoming longer. During this time, the hormones that birds produce are stimulated, and they know it is time to make their journey. Birds begin to display migratory restlessness (also known as Zugunruhe).
Even caged birds know when it is time to migrate. In a study conducted by Stephen Emlen, migratory birds were placed in what is now known as an Emlen funnel – a cone-shaped paper device – with an ink pad bottom. The device was placed outside or underneath a planetarium display so that the birds could see star patterns. The birds would try to take off in the proper migratory direction.
However, if the funnel was placed beneath a planetarium display that was flipped by 180 degrees, the birds would take off in the opposite direction.
As for the exact day that birds choose to migrate, this can depend on the availability of food, and the current weather conditions with regard to rain, wind, and barometric pressure. In addition, different bird species may migrate at different times.
3. Birds Fatten Up to Prepare for Bird Migration
How do birds prepare to migrate?
Once birds are ready to migrate, their main goal is to quickly fatten up via a process called hyperphagia. During this time, birds will intensely feed, gorging themselves and gaining significant weight to fuel their arduous migration journey.
Migrating birds can also undergo massive changes in physiology as well, with pectoral and heart muscles increasing, and legs swelling.
During migration, fat fuels their flight. The importance of fuel is especially salient for long-distance migrants who will fly non-stop covering vast distances before stopping en route.
When the fat supply starts to dwindle, migrating birds will visit birding hotspots, also called migration traps and staging sights. These hotspots will supply them with food and shelter. They will enter a state of hyperphagia once again, and fatten up and rest to continue their journey.
Recent research suggests that migratory birds are also boosting their immune systems during these pit stops, taking a break from the exertion required by long-distance migration.
Arne Hegeman, one of the co-authors of a February 2023 study has stated that “Our study shows that migratory birds’ stops serve other purposes, besides just ‘refueling.’ They also need other physiological systems to recover. You could compare it to pulling off the motorway into a service station. That is not just for the purpose of refueling, you might also need to recover.”
4. Birds Navigate Via Celestial Cues and Mental Maps
How do birds navigate during migration?
Birds navigate using a combination of visual and non-visual methods. Two visual methods include using celestial cues and known landmarks that exist within topographical mental maps.
When using celestial navigation cues, birds will use the position of the sun, stars, and moon. Even before the first migration, birds know where the North is by locating the North Star and the stars around it.
Birds can also use the setting sun to get compass information during the day. By tracking celestial positions, birds can stay on course during migration.
After a bird’s first migration, it will build a mental map of the flight path and use it on subsequent migratory flights, recognizing known landmarks. For example, some bird species use known landmarks such as coastlines or mountain ranges to navigate.
A bird may also learn migration routes from its parents or other birds. This acquired knowledge, combined with other navigational techniques, will allow it to perfect its migratory flight acumen.
5. Birds Navigate Via Magnetoreception and Instinct
How do birds navigate during migration? Can birds see magnetic fields?
Birds can detect and use the earth’s magnetic field to navigate. Research suggests that, via a protein in their eyes, they may be able to “see” and follow magnetic field lines. They may also be able to use the magnetite in their bills to sense the magnetic field.
As for instinctual knowledge, young birds will typically make their initial migratory journey flying solo. During this time, they are following instructions inherited from their parents. Since this is their first journey, they have not yet built up a topographical map that they can use to navigate. As a result, this first migration is particularly risky.
Birds may also use nocturnal flight calls from other migrating birds to help guide their ways. In addition, they may use olfactory cues from habitats.
6. Birds Follow the Migration Flyways
When birds migrate, do they follow a specific path?
When birds migrate, they follow established migratory routes called Flyways. Think of them as super highways for birds! In North America, there are 4 main migration flyways: Pacific Flyway, Central Flyway, Mississippi Flyway, and Atlantic Flyway. They cover major cities as well as suburban and rural areas.
If we looked at a topographic map of these 4 migration flyways, we might see that they have something in common – they follow geographical features such as coastlines, mountains, and rivers.
They also include birding hotspots (also called stopovers and migration traps) and refuges in urban areas, as well as in suburban and rural locations. Hotspots are places that offer birds natural food, water, and shelter. Refuges are specifically designed for this purpose.
Many migrating birds like to visit hotspots and refuges so they can rest during a long and demanding journey, and eat to refuel. Birders like visiting these hotspots to see a large concentration and variety of birds, especially during fall and spring migration.
City birders especially appreciate these areas, which are wonderful bird sanctuaries in the middle of bustling urban areas.
7. Birds Use Different Migration Methods and Patterns
Do all birds migrate in the same way?
Some birds make seasonal short-distance migrations, while others travel long distances when migrating. Most of these journeys are latitudinal, following north/south directions along flyways. Latitudinal migration, where birds fly east/west, is less common.
Altitudinal migrants stay in the same geographic locations, but migrate up and down mountains, or from mountains to valleys so that they can breed and feed at various elevations. The image below is from a 2013 study “Partial Altitudinal Migration of a Himalayan Forest Pheasant” by Norbu et al. The image shows the color-coded migration patterns for 8 individual tragopans (commonly called horned pheasants) up and down mountainous terrain over the course of summer and winter migration periods.
Finally, within a bird species, only some of the birds may choose to migrate. This is referred to as Partial migration.
During migration, birds may also exhibit a variety of patterns with regard to route consistency, distance and direction traveled, and migration triggers:
- Loop migrants use different routes on their destinations and return journeys.
- Leapfrog migrants travel to areas further north and south than other migrant bird destinations.
- Reverse migrants migrate in a direction that is different or opposite to the one they typically take.
- Molt migrants migrate to a safe location to wait for new feathers to come in after molting.
- Drift migrants drift or alter course due to winds, often when migrating along the coast.
- Irruptive migrants respond to food shortages by migrating to a location that is different from their typical migration destination.
- Irregular migrants migrate only when there is a food shortage.
8. Most Migration Occurs in the Northern Hemisphere
Does bird migration occur in both the northern and southern hemispheres?
More migration occurs in the northern hemisphere than in the southern hemisphere due to a variety of factors. First, the northern hemisphere has more landmasses than the southern hemisphere, while the southern hemisphere has more ocean area.
Specifically, the northern hemisphere contains around 67% of the world’s landmass, while the southern hemisphere contains around 33%.
The prevalence of landmasses in the northern hemisphere, and the fact that they are connected, makes it easier for birds to migrate in the northern hemisphere – they can rest and feed along the way.
The northern hemisphere also contains more diverse habitats for birds to migrate to for better food sources and breeding in the spring. Temperature also comes into play – In the fall and winter, the northern hemisphere is colder than the southern hemisphere and so birds migrate back to warmer locations.
9. Most Migration is Nocturnal
Do birds migrate at night?
Most birds migrate at night. There are several reasons for this. First, it is more difficult to fly during the day due to heat and air turbulence. In addition, when birds fly at night they can avoid birds of prey who hunt during the day, as well as ground predators.
Birds also fly at night because they can use celestial cues to navigate. Their ability to detect the earth’s magnetic field and to “see” and orient themselves along magnetic field lines may also be more salient in the evening since there is less distraction from other types of inputs.
Flying at night also allows them to eat food during the day when they visit hotspots and refuges.
Finally, when birds migrate at night they cannot use the updrafts created by rising air that allows them to soar. Instead, they must propel themselves and keep alight by flapping their wings. As it turns out, wing flapping is a more efficient method of flying and so allows them to conserve energy.
Birds who migrate during the day are called diurnal migrants. Diurnal migrant birds with large and broad wings, such as birds of prey, herons, and storks, soar via daytime thermals. Some smaller birds, including robins, tits, and some types of finches, may migrate primarily during the day as well.
10. Not All Birds Migrate at the Same Time
Do all birds migrate at the same time?
Even though many bird species migrate at specific times, the timing of migration across species can significantly differ. The timing of migration is often dependent on not just the time of year, but on a variety of factors including the distance to breeding and wintering grounds, and the characteristics of their location.
Specifically, the environmental cues that trigger migration will vary depending on the departing location.
Some birds may also time their migration to coincide with food availability at their destination location and may leave earlier in order to find optimal breeding grounds and mates. They may also depart at an earlier date so that they don’t run into birds of prey who appear later in the season.
Finally, the timing of migration can also be influenced by genetic variations in a bird species.
11. Most Birds Migrate in Flocks
Do all birds migrate in flocks?
The common perception of bird migration is that all birds migrate in flocks. We often think of the V-shaped pattern we see in the sky when a flock of birds soars overhead. While it is true that most birds migrate in flocks, not all birds do. However, there are many advantages to migrating in a large group.
Birds will migrate in flocks for various reasons, including safety, navigation, and energy conservation. For example, birds that fly in groups have a better chance of detecting predators and keeping an eye out for one another.
Flying in a flock also makes navigation easier since the route is determined by shared knowledge instead of the knowledge of an individual bird. By taking turns leading the flock, and taking advantage of air currents, energy can be conserved and flying speed faster. Finally, social birds tend to navigate in flocks.
Less social birds tend to navigate on their own. Birds may also migrate alone if they want to set up breeding grounds prior to the arrival of potential mates. Territorial birds are more likely to migrate alone as well.
12. Technology Tells Us Where Birds Go
What role has technology played in our understanding of bird migration?
Technology has helped us to understand so much about bird migration. Bird banding, satellite tagging and tracking, GPS tagging and geolocators, and radar detection technologies have significantly advanced our understanding in the following ways:
- Satellite tagging and tracking – Small tracking devices that transmit signals to satellites are attached to birds. Tracking of these signals provides data about the location, speed, and altitude of migrating birds, allowing us to discover migration patterns that take place over vast distances and over and across inaccessible areas like oceans and deserts.
- GPS tagging and geolocators – A small GPS device is attached to a bird, recording its location at specific intervals. This technology has been used to understand the real-time movement of migratory birds, the migration routes they take, and the habitats they visit.
- Radar-detection – Radar signals provide information about birds as they move through the air. This data makes it possible to estimate the number of birds in a specific location, how high they are flying, and the direction they are traveling in.
- Bird banding – Small metal bands that contain unique ID numbers are affixed to the bird’s legs. When a bird is found, the band can be used to track its movements and lifespan. This data has been used for years, providing fantastic information about migration routes and timing.
13. Migration is Impacted by Climate Change
Does climate change affect bird migration?
Climate change is definitely impacting bird migration. Climate change affects the timing of seasons, meaning that some birds may migrate earlier, as well as the availability of food and nesting sites at breeding locations.
Since food and nesting sites are impacted, birds may need to change their migratory routes to search for better locations. If they travel to known sites where the resources are now limited, this will negatively impact the chances of survival for both them and their offspring.
We all know that climate change has resulted in unpredictable weather patterns, including more storms, and storms that are more severe. Even an experienced migratory bird, let alone a young bird, flying through severe weather will find the experience challenging and perhaps even life-threatening.
14. Migration is Dangerous for Birds
Is migration dangerous for birds?
During long-distance migration, the journey can be perilous. Bird migration is a dangerous endeavor due to the following reasons:
- Light Pollution: Birds may crash into the windows of city buildings that they mistake for starlight. Hi-rise buildings in urban areas are a significant threat to birds.
- Inclement Weather: When birds fly through rough weather they can become disoriented and exhausted
- Stress: The stress of long-distance migration takes its toll. Birds may become dehydrated, and weak.
- Predators: During migratory flights, or when resting, birds can be attacked by predatory birds. When resting, birds can also be attacked by cats and dogs.
- Habitat loss: Loss of habitats is dangerous for migrating birds who rely on them for rest and refueling
- Hunting: Sadly, human hunting of migratory birds is one of their most significant threats
15. Protection of Migrant Birds is Important
Why is protecting migrating birds important?
Protection of migratory birds is important for a number of reasons, including the ecological role they play, the threats they face, and their cultural importance.
Birds play a significant role in maintaining the balance of ecosystems. Without birds, it would be difficult to control insect populations. Birds also disperse seeds and pollinate plants. In addition, predators such as raptors use migratory birds as a major food source.
Unfortunately, migration is a journey fraught with danger. The combination of climate change, collisions with buildings and wind turbines, hunting, and habitat loss has a significant negative impact on migratory bird populations.
Finally, birdwatching and ecotourism are popular and enjoyable activities. Without birds, our world would be a sad place.
To educate yourself about the dangers of migrating birds and how you can help, learn more here.
16. Artic Tern & Bar-Tailed Godwit- Migrant Superstars
Are some birds better at migrating than others?
The navigational feats of some migratory birds stand-out above all others. Some birds are migrant superstars, covering vast distances, and making impressive non-stop flights.
The arctic tern is one such migrant superstar, traveling from its breeding grounds in the Arctic to the Antarctic coast for the summer months. The roundtrip journey, covering vast expanses of ocean and changing weather conditions, can cover as much as 56,000 miles.
The journey is so extensive that over the course of its life, an arctic tern may travel up to 1.5 million miles.
Another migrant superstar is the bar-tailed godwit. This extraordinary bird makes a record-breaking flight of approximately 7,000 miles, from Alaska to New Zealand, without stopping.
The journey takes up to 11 days. The bar-tailed godwit’s streamlined body shape reduces drag. In addition, its muscle fibers help it to travel non-stop and store large amounts of energy.
17. The Best Time to Go Birding is During Fall and Spring Migration
When is the best time to go birding?
Birding is always fun, and I bird in all seasons. That being said, I particularly enjoy birdwatching in the fall and spring, during migration. During seasonal migration periods, you can see an amazing variety of birds that you don’t see during other times of the year.
Right now it’s early spring in North Carolina, and I have bright yellow Warblers in my backyard. It’s thrilling to see and hear them, and to watch them hang out in the treetops with my resident birds.
Urban birders who are near birding hotspots and refuges can also take advantage of the seasonal spectacle of migrating birds. Many large cities have incredible birding hotspots in their city centers, in the form of large parks, walking trails along waterways, and wetlands.
Large cities also have numerous birding tours that occur during migration as well as year-round. (The birding tours in New York City are excellent).
Even city cemeteries can be amazing places to observe migrating birds.
This is also an exciting time to observe birds in suburban backyards as well as apartment balconies that have been transformed into small bird habitats that include water sources, native plants, and bird feeders.
18. People Once Thought Birds Hibernated or Transmuted
Have we always known that birds migrate?
People didn’t always know that birds migrate from one location to another. At one point in the distant past, it was thought that when birds disappeared from an area, they were burrowing down in mud found at the bottom of ponds, and re-emerging a few months later.
There was also a theory that birds mutated into other species. This was based on the observation that when birds left a location, other birds, fish, and animals suddenly appeared. So, for example, if robins departed an area at the same time that certain fish showed up, it was thought that the robins had transmuted into the fish.
As fantastical as these theories sound to us, the fact that birds are actually making round-trip seasonal migration journeys that require them to travel thousands of miles would have seemed even more incredulous to the proponents of mud-hibernation and transmogrification theories.
Final Words on Bird Migration
I hope you have enjoyed this article and learned more about the fascinating phenomenon of bird migration. It’s amazing how much there is to learn, and how rich and extraordinary this domain can be.
My pondside backyard is on a pond and adjacent to a large lake. Birdwatching binoculars in hand, I enjoy watching the antics of migrating birds of all kinds that visit my little bird sanctuary. Friends who visit during this time will often ask me questions about bird migration and I find their queries fascinating.
I find it interesting that, to the casual observer, large groups of birds soaring overhead during certain times of the year may not even register as a significant event.
In fact, even birders who know a bit about seasonal migration are often not aware of the full scope of the topic. I count myself as one of them, still learning and enjoying every minute of it!
If you find this topic interesting (and I assume you may if you have it to the end of this post) then I encourage you to learn more by taking guided birding tours during spring and fall migration. I also suggest visiting birding hotspots and refuges in your area to take advantage of this magical time.
Why do birds migrate?
Birds migrate to seek better food resources, more daylight, superior nesting sites, fewer predators and parasites, and a more temperate climate. The primary motivation is the survival of birds and their future offspring, which depends on finding the best habitat to breed and raise their young.
How do birds migrate during migration?
Birds orient themselves by using celestial cues, the earth’s magnetic field, mental maps, and other sensory inputs such as nocturnal calls and olfactory cues.
What are the different types of bird migration?
Birds may be short- or long-distance migrants that primarily conduct longitudinal journeys or altitudinal migrants who visit various elevations. Birds may also use different migration patterns such as reverse, irregular, irruptive, looping, leap-frogging, molting, and drifting.
What are the threats to bird migration?
Migratory birds face threats from inclement weather, the stress of an arduous journey, attack from predators, loss of habitat, artificial light from buildings that can distract and disorient them, and being hunted by humans.