House swallows are a migratory bird that spends their summers in Europe and China, respectively, before embarking on a long journey south in the fall.

For European house swallows, this journey is particularly arduous as they must cross the vast Sahara Desert in Africa without any opportunities to rest along the way.

In contrast, Chinese house swallows tend to stay in Guangdong/Yunnan for the winter, with only a small minority flying out of China to South Asia, Southeast Asia, and Australia.

They do not return to the north until March to May of the following year. Despite the challenges of migration, swallows have developed various strategies to ensure their successful return to their nests in the spring.

Studies have shown that the probability of a successful return to the nest for northern swallows in the spring is approximately 47%.

Two critical factors that impact the success rate of their return are energy and navigation. When the migration season approaches, swallows exhibit "migration excitement," a behavior triggered by the change in daylight hours.

Swallows instinctively stimulate the "gene" in their body that regulates overeating and will eat excessively to accumulate fat for their next oceanic migration.

To complete the journey successfully swallows need to have sufficient energy stored in their bodies.

For example, a bird weighing 100 grams will consume about 1 gram of fat for every 54 kilometers of flight.

However, energy storage is only half of the equation. Swallows also need to be able to navigate accurately and reach their destination.

Many scholars have been studying and exploring the swallows' ability to navigate, and various theoretical theories have emerged over the years.

In the 21st century, the discovery of the magnetic sensing protein MagR receptor and cry has made the famous geomagnetic induction theory more widely accepted.

The principle of geomagnetic induction is that the geomagnetic/biological protein/bird migration/quantum mechanics work together.

The deeper investigation of this theory is complex, but it is widely believed that swallows can "see" the Earth's magnetic field.

However, "seeing" here does not mean that the swallow can physically see the Earth's magnetic field. Instead, geomagnetism affects the reaction conversion rate of certain free radicals in the swallow's body, allowing it to perceive the direction of geomagnetism.

This perception, combined with the role of photoreceptor protein on the real scene in its retina, allows the swallow to form a real-time angle.

Therefore, the swallow perceives the angle between the geomagnetic vector and the horizon through its vestibular system, which helps it distinguish north from south and navigate accurately.

In addition to the sense of direction provided by the Earth's magnetic field, swallows may also use their sense of smell, tactile senses, and strong memory to navigate.

These aspects are currently being studied by various scholars.

House swallows have developed several survival strategies to ensure their successful migration, which includes overeating to store enough energy, navigating by using the Earth's magnetic field, and using other senses such as smell and touch.

The migration of these birds is an incredible feat that demonstrates the complexity of the natural world and highlights the importance of biodiversity conservation.