How Do Birds Know To Fly South?

By Richard Worden


Bird migration is an exciting phenomenon. They seem to have an internalized compass that accurately guides them during the migratory seasons. However, birds use a combination of methods to determine direction.

So how do birds know to fly south when migrating? 

Birds know how to fly south through methods such as following the sun’s position during the day or the star constellations by night. Birds may also determine direction using the earth’s magnetic field by following their sense of smell or identifying landmarks near their destination.

This article will shed more light on how birds know how to fly south. I will explain how the birds use each highlighted method to determine direction. I will also explore why birds migrate and the preparation process that birds undertake before migrating.

how do birds know to fly south


How Do Birds Know The Direction To Migrate?

Unlike us, birds do not rely on maps or GPS systems to accurately determine direction. Instead, they are guided by a series of natural factors that are both internal and environmental.

Let’s explore how do birds know to fly south...

Following the Sun’s Position During the Day

How do they do this?

Birds have a biological rhythm (also called a biological clock function) that causes them to react to momentary environmental changes, such as the effects of the earth’s rotation around the sun. 

This internal mechanism affects the birds in different ways. It affects their:

  • Migration patterns
  • Vision
  • Sleep and wake time
  • Reproduction patterns
  • Seasonal song patterns

Therefore, birds can determine the geographical south and move in this direction based on the sun's position.

Following Star Constellations by Night

Most birds migrate at night, during which they rely on another celestial cue: stars. Before maps and compasses were invented, sailors relied on this navigation method too. But how does this celestial cue help birds navigate in a southward direction?

During clear nights, birds use the orientation of stars to guide their movement.

This study conducted by a Cornell University researcher using Indigo Buntings revealed that the migratory patterns of birds shifted with changing star patterns. The researcher concluded this after conducting experiments inside an artificial planetarium sky (in which the stellar arrangement could be altered to different directions), where shifting the stellar cues resulted in a shift in the migratory path of the birds.

However, the research also noted that this behavior is not consistent for all birds, and only some of them rely on star constellations for navigation.

Using the Earth’s Magnetic Field

The earth’s magnetic field emanates from its liquid iron core which creates strong electric currents, resulting in a magnetic field (extending to outer space). Some birds use this as a guide to orient themselves southward.

Scientists have not come to a complete consensus on how birds exploit the earth’s magnetic field during migration. That said, several experiments have concluded that shifts in the earth’s magnetic field cause a change in the migratory patterns of birds.

There are two plausible suggestions that have been brought forward as to how do birds know to fly south:

  • The presence of magnetite-based magnetoreceptors in the beaks of birds such as pigeons help them navigate during migration.
  • Cry4 protein in birds’ eyes helps them perceive the earth’s magnetic fields and use this to orient themselves in a southward direction.

Following Their Sense of Smell

For the longest time, birds were thought to have a poor sense of smell. However, recent research shows that some birds, such as seabirds, rely heavily on their sense of smell to navigate long, unfamiliar distances that don’t have landmarks (for example, when traveling over seas and oceans).

A study conducted on shearwater birds concluded that these birds do rely on their sense of smell when traveling over oceans. The experiment was conducted by separating the birds into three separate groups. The first group had their sense of smell impaired using 4% Zinc Sulfate. The second group of birds had their magnetoreceptors inhibited, and the last group of birds was left to fly unimpaired.

The findings showed that the sense of smell played a significant role in the navigation of shearwaters.

Identifying Landmarks

Birds identify landmarks such as rivers and mountain ranges along routes that they have previously traveled. These landmarks serve as guides during future trips. However, this is only possible for birds that migrate during the day.

One factor that helps birds identify landmarks during migration is their good eyesight, which enables them to see far-off objects in great detail.

Additionally, the bird’s eye view helps them map out landmarks such as rivers that span larger areas, helping them navigate better in future trips.

Here's an interesting YouTube video
that discusses bird migration...


Why Do Birds Fly South For The Winter?

Part of understanding the migratory habits of birds is figuring out why they need to migrate. To begin with, not all birds are migratory birds. Those birds that do not migrate are referred to as permanent residents.

Moreover, among the migratory birds, some travel long distances, while others travel over medium or shorter lengths. Even so, their reasons for migrating southward are mostly similar:

  • The greatest motivation for avian migration is to seek food and safe shelter. Some birds may also migrate to escape the freezing winter weather. However, other birds, such as hummingbirds, can withstand low temperatures as long as they can access food. 
  • Birds also migrate to seek out favorable conditions for breeding. This is because breeding is unlikely to succeed when food is scarce due to undernourished birds and hatchlings. On the other hand, healthy birds and hatchlings will have better chances to survive and thrive.
  • Predators also motivate birds to migrate. If birds lurk for too long in the same region, they may attract more predators, threatening their population. Therefore, migrating southward helps to keep them safe.
  • Bird migration also lowers the prevalence and spreading of pests and diseases. This is so because birds that crowd in one place for extended periods are more likely to transmit pests and diseases to each other.

During their migration, birds move from the North towards tropical regions in the South. This happens just before winter begins since this is when food sources such as insects and plants dwindle. 

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So during the winter, what birds migrate? Here's a fascinating article explaining which birds do or don't fly south and why.

How Birds Prepare To Migrate Southward

The migration process requires a lot of energy and stamina from the birds. So, they must adequately prepare for the journey. 

Depending on whether they will be traveling for short or longer distances, preparation methods may differ among the migratory birds. Here are some steps that birds take to prepare for the migration process:

Molting

Molting is the shedding of old or damaged feathers by birds so that healthy feathers can grow in their place. This process is crucial for migratory birds because it helps them to fly better and for longer distances. Old or damaged feathers are a flying hazard because they cause more air resistance hence make flying more challenging.

Fattening Up

As mentioned earlier, birds need all the energy they can get before migration. This is especially so for birds that fly non-stop until they arrive at their destination. For this reason, birds may even double their weight by changing their diet to feature foods that will help them build up fat stores.

Even so, not all birds need to amass fat before migrating since some incorporate several stopovers to feed. This process is therefore necessary for birds that travel long distances non-stop, such as the bar-tailed godwit that travels southward from Alaska to New Zealand.

Nonetheless, birds need to remain light enough to fly. Otherwise, they will struggle through the entire journey or need to eat more to get the energy they need to fly while heavy.

Adjusting Sleep Patterns

During migration, birds need to adjust to sleeping less. This adaptation helps them remain alert to avoid dangers such as predators and collisions. By sleeping less and adopting a nocturnal nature, they are also able to cover longer distances and arrive at their destination in less time.

Adaptation of Internal Organs for Long Flight

This is another exciting way birds prepare for a long flight. To accommodate the fat they need to put on without interfering with their flight ability, some of the bird’s internal organs shrink, while others increase in volume. This internal organ adaptation helps to distribute fat evenly, enabling the bird to retain its flight ability.

How Do Birds Know To Fly South...Conclusion

Birds use a combination of factors to aid their migration to the south. For instance, some bird species may rely on specific navigation guides as they migrate. In other cases, the extent to which the birds rely on distinct guides remains undetermined.

The main reason birds fly southward is to seek resources for their survival. These include food and a safe nesting ground. With these in place, they can breed, reproduce, and thrive.

To prepare for the migration process, birds need to store enough fat to produce sufficient energy for the journey. 

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About Me


About the Author...
Richard Worden, a dedicated bird lover for over 20 years, I love to share my in-depth knowledge and passion for birds. Read more About Me and my expertise in this field.

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