Bird Migration refers to the practice of several species of birds to change their geographical location seasonally. It is common to spot migratory birds in the sky, especially during the spring and fall season. Migration takes places because birds seek new places where the climate is not harsh and there is abundant food and water to survive and raise the young ones.
These are some lesser known facts about these types of birds.
Migratory Species
The known number of species of migratory birds currently stands at 4000. This number is about 40% of the total number of bird species in the world. As more species of such birds are discovered, this number will increase.
Distances Covered
They cover long distances ranging from hundreds to thousands of miles. Arctic Tern covers the longest distance from Greenland to Antarctica. The average distance covered by Arctic Tern is a whopping 44,000 miles. Northern wheatear is a songbird which covers 9000 miles from Arctic to Africa, thereby making it one of the few songbirds to cover such a large distance.
Speed
Most of the birds fly at a speed of 20-30 miles per hour. The fastest among all migratory birds is the great snipe which travels at a speed of 60 miles per hour over a distance of 4200 miles. These birds can cover as much as 600 miles in a day.
Direction of Travel
These birds use the position of the sun to navigate during their travels. The magnetic field of the Earth is utilized by some species such as homing pigeons to navigate. The magnetic field is used by magnetite present in the beak of such birds. Migratory birds that fly at night use the position of stars with respect to constellations to navigate.
Height Of Migratory Birds
This kind of bird flies at altitudes of less than 2000 feet. Songbirds fly at an altitude ranging between 500 and 2000 feet. Bar-headed goose can fly at an altitude of more than 30,000 feet above sea level. It flies above the Himalayan Mountains in its migratory route. High altitude enables birds to glide instead of flapping their wings which conserves energy.
Increasing Weight Before Migrating Birds
There are many birds which increase their body weight before commencing the long journey. The hormone levels spur the birds to increase fat storage during the weeks preceding the journey. The stored fat is utilized by the bird to get energy during migration. Some species double their weight before commencing travel.
Migratory Birds Triggers
Migration triggers or signs that suggest to the birds that the time to migrate has come varies from species to species. However, there are some common factors such as temperature changes, length of the day and scarcity of food which act as migratory triggers for birds.
Threats To Migratory Birds
These birds face a lot of threats during the journey. These include predators, collisions, dehydration, starvation, drastic changes in climate, windmills, power stations, etc. Humans also pose a big threat to these birds. Millions of birds are hunted and captured by humans each year.