Explained: Why do birds migrate?

New Delhi, Apr 15: Summer is here. You would be mesmerised with the wrinkled V-shaped flocks in the sky. The brightly coloured birds embarking on their annual migration is a delight to watch. And ofcourse, bird lovers all excited to hear the sound of a new bird that they never heard off.

India is temporary home to several migratory animals and birds. Most of the migratory bird species that make their way to India in the summer often migrate from a region with low resources to one with high resources. In India, summers are not too harsh and food is plenty, making it ideal for birds to spend the hot summer months.

What are migratory birds? Why do they migrate?

Migratory species are those animals that move from one habitat to another during different times of the year, due to various factors such as food, sunlight, temperature, climate, etc. The movement between habitats, can sometimes exceed thousands of miles/kilometres for some migratory birds and mammals. A migratory route can involve nesting and also requires the availability of habitats before and after each migration.

The timing of migration seems to be controlled primarily by changes in day length. Migrating birds navigate using celestial cues from the sun and stars, the earth's magnetic field, and mental maps.

How do birds migrate:

Permanent residents: These birds do not migrate as they find adequate supplies of food year-round.

Short-distance migrants: These birds make relatively small movements, as from higher to lower elevations on a mountainside.

Medium-distance migrants: They travel and cover a few hundred miles.

Long-distance migrants: They take arduous journey from country to country to find the best ecological conditions and habitats for feeding, breeding and raising their young.

How fast do migrating birds fly?

The speed of flight depends largely on the species and the type of terrain covered.

How high do migrating birds fly?

According to Texas Parks & Wildlife Department, "Most migrants fly at low altitudes, usually below 7400 feet. Small birds migrating at night fly between 800-1600 feet. In the daytime they fly much lower, often below 200 feet. Some fly much higher, the record is held by the Bar-headed Goose: 29,500 feet above sea level, over the Himalayas in India."

Birds that migrate to India

Important birds that migrate include Amur Falcons, Bar headed Gheese, Black necked cranes, Marine turtles, Dugongs, Humpbacked Whales, etc. The Indian sub-continent is also part of the major bird flyway network, i.e, the Central Asian Flyway (CAF) that covers areas between the Arctic and Indian Oceans, and covers at least 279 populations of 182 migratory water bird species, including 29 globally threatened species.

India has also launched the National Action Plan for conservation of migratory species under the Central Asian Flyway.