Heungbu and Nolbu, an old Korean novel, contains scientific knowledge of migratory birds. This novel is about a kind man named Heungbu, who takes care of a baby swallow that had its leg broken by falling to the ground from its nest. The baby swallow leaves for a long journey in the autumn, and the next spring it comes back for Heungbu with a seed, which grows to be a gourd full of gemstones inside.
Animals’ instinct to leave for far-off places from their habitats and come back to their original locations is called homing instinct. Just as it is shown in the novel, Heungbu and Nolbu, the swallow has an amazing homing instinct. A few years ago, a bird expert attached rings in ten swallows’ legs to experiment their homing ability. The next spring, to his surprise, six out of the ten swallows came back to their original nests.
Migratory birds have different places for breeding and for spending winter. However, they do not look for new places for breeding or for spending winter every time. Instead, they always travel the same routes with their outstanding homing ability. Birds like swallows, cuckoos, egrets, and nightingales spend winter in Southeast Asia or southern China, and fly to Korea in spring and breed there. On the other hand, birds like Baikal teals, geese, and red-crowned cranes breed in the northern part such as Manchuria and Siberia, fly to Korea in autumn, and spend the winter there. In the past, people didn’t know birds’ migration, so they used to have a funny imagination that the “birds hide in the ground in the winter.” It wasn’t until the 20th century when the secret of birds’ migration was revealed through rings or satellite radio transmitter or radar.
Pigeons, though not migratory birds, are also famous for finding the exact way home from distant places. In the time when communication means was not developed, people sent and received letters by using pigeons as carriers. Also, doves which are from the same bird family as pigeons are mentioned in the Bible. After Noah escaped the flood, he sent a dove to see if the water had receded, and the dove came back to the ark with an olive leaf in its beak.
The salmon is one of the typical migratory fish. Salmon are born in freshwater, but spend most of their lives in the sea. Then, they come back to the stream where they were born to spawn. On the contrary, eels, born in the sea, live most of their lives in the freshwater, but they eventually go back to the sea to spawn. After hatching, baby eels make an accurate way back to the rivers where their moms lived.
Pets such as dogs and cats have homing instinct, too. In Korea, a Jindo dog that was sold to a city traveled over 300 km [186 mi] for seven months to come back home. A cat that was lost while traveling with its owner came back home that was 321 km [199 mi] away after two months; when the cat came home, its paws were covered with blood and its claws were almost gone. Bees and ants too have homing instinct; ants excrete chemical materials called pheromones1 and find their way home by its smell.
1. Pheromone: a chemical substance released by an animal, affecting the behavior or physiology of others of its species. There are bees’ group pheromones and ants’ pheromones that guide the way.
The distance does not matter in returning home. Some birds and fish travel relatively short distances, but quite many travel a long distance. Monarch butterflies travel 5,000 km [3,100 mi] from the United States to Mexico with their tiny, delicate wings. Among hummingbirds which are the smallest bird with 5 cm [2 in] length, some travel even 850 km [528 mi] in one trip.
Migratory birds travel thousands or tens of thousands of kilometers to go home. Baikal teals travel 4,000 km [2,500 mi] to South Korea from Siberia to spend the winter. Among birds, the one that travels the longest distance is the arctic tern that lives in the Arctic. Arctic terns leave the Arctic to make a trip to the Antarctic and come back every year. Each roundtrip is about 70,000 km [43,500 mi] long. The distance that they travel for their lifetime of thirty years is equal to that of traveling to the moon back and forth three times. Salmons also swim tens of thousands of kilometers in the Pacific Ocean and go back to where they were born.
It is still not known clearly how birds and fish travel such long distances accurately with no maps, or compass, or GPS. According to the results of researches, it seems that they use the constellations or the moon or the sun as their index direction, or find a way through clear geographic features or smell, or receive help from an invisible force called Earth’s magnetic field.
Although they have outstanding sense and ability, not many of them make it back home safely. There is only 1% of possibility for a salmon to return to the upper reaches of rivers where they were born. Some are eaten by bigger fish or birds while growing up, and also the way home is not easy at all; they have to avoid attacks from their enemies, and swim through strong waterfalls or obstacles like rocks. There are countless difficulties and obstacles during birds’ migration, too. They need much energy to travel a long distance. If they do not find food on their way, they become exhausted and die. Also, since they do not have the ability to predict the weather, they sometimes lose their lives due to weather such as storm, blizzard, fog, and heavy rain. However, they do not stop making journeys home. No matter how far they have to travel, and no matter how many obstacles they face, they still make their way home.
Homing animals make a thorough preparation and help each other to go home. Once salmon reach the estuary of a river, they take some time to change their bodies to be appropriate to live in the river water. Most fish live only in fresh water or only in salt water, but the fish that travel the sea and fresh water back and forth such as salmon and eels need to adapt themselves to the change of salt concentration. When you see how a fresh cabbage becomes soggy when it is salted, we can understand the environmental change caused by the difference of salt. To overcome such an environmental change, salmon and eels go through a physiologic adaptation process called osmoregulation in brackish water2 for a long time, so that they can spawn.
2. Brackish water zone: a zone where fresh water and sea water get mixed freely. It has broad salt concentration between 0.5–30‰, and it has dramatic changes, depending on the weather or precipitation. (Generally, water below 0.5‰ of salt concentration is called fresh water, and water over 30‰ is called sea water.)
As for migratory birds, they store fat, which is like fuel, in their bodies before flying a long distance. After taking in more food than usual, they change excess nutrients into fat and accumulate it in their bodies. Red knots, which travel for about 30,000 km [18,640 mi] a year, double their weight for ten days prior to migration. Nightingales, too, which are migratory birds of Sweden, accumulate fat, the fuel for flight in their bodies just as a car is filled with gas, in Egypt right before crossing the Sahara, which is 1,500 km [930 mi] long, to reach the central-southern part of Africa.
Migratory birds fly in a V-shaped formation, depending on each other’s wing flapping, so that they can fly far with small strength; when the bird in front flaps its wings in the V-shaped formation, the bird in the back can use the air flow created by the front bird and float in the sky for a long time with smaller flaps of the wings. An experiment shows that the birds flying in a V formation use 11 to 14% less energy, compared with the birds flying alone.
The reason animals’ life of heading home seems special is that the meaning of home is great for people, the lord of all creation, too, without a doubt. Students who study abroad and immigrants miss their home countries, and sometimes they suffer from homesickness. Displaced people, who cannot go home though they want to, live all their lives, crying on the inside.
Mankind has been trying for a long time to find out the reason animals seek their homes. However, we’ve only grasped vague outlines. We only explain it as the ability that they are born with, meaning, an instinct. It means that they naturally head home just as a baby is not taught to suck milk but still does. Why is it that many animals and humans have this homing instinct?
“Even the stork in the sky knows her appointed seasons, and the dove, the swift and the thrush observe the time of their migration. But my people do not know the requirements of the LORD.” Jer 8:7
“If they had been thinking of the country they had left, they would have had opportunity to return. Instead, they were longing for a better country—a heavenly one.” Heb 11:15–16