Most of the time, when we hear the word 'Migration',  a picture of a silhouette of a group of birds flying across the blue sky in a V-shaped formation pops in our mind. We have seen this scene in our lives a number of times. These birds would fly over, making a lot of chirping and flapping noises along the way, fading into the horizon. You probably know that they are flying to the same place again for breeding where they were once born. But have you ever wondered just how they are able to find their way back to the precise place year after year, without the use of a GPS or compass and how their body is able to cover such long distances? Today, we are going to learn just that.
Migration is the movement of an individual or group away from its place of origin or centre of population density, involving regularity and returning pattern. For most of the birds, it is usually an annual repeated seasonal movement between breeding and non breeding place. Migration can be of several types but I'm not going to bore you and waste your time with such details. I have simply shown the type of migrations with their details in the info graphics below.

These migrating birds have shown several adaptations for their migration. These adaptations are both morphological as well as physiological. The wings have adopted for prolonged and horizontal flight. Long-distance migrants have highly convex and pointed wings which helps them to glide over long distances without flapping their wings too much. The composition of the flight muscles have also changed for long flight.The weight distribution of the fat has become more suitable for better aerodynamics. The proportion of the flight muscle are composed of more oxidative glycolate fibres in the migrants.The senses usually are listed as five in number: touch, taste, smell, sight, and hearing. Birds and many other kinds of organisms possess more senses than these (e.g.
ability to detect and respond to differences in Earth’s magnetic field and in wind direction) and are able to use them to know where they are going, where they have been, and how to travel between them. There are several physiological adaptation as well. Physiological adaptation such as higher song rates, larger reproductive organs, faster growth rate, brighter plumage than average represent the adaptation for a migrant lifestyle. Short term defence of territories by the terrestrial non colonial migrants, higher rates of successive polygamy and extra pair fertilization, higher size and more successful clutches per season, shorter incubation period and nesting periods are some more of these adaptations changes in migratory birds.

Although a lot has been learned from the information collected from these migratory birds, we still don't know how are they able to navigate so precisely to their breeding ground year after year.  Ornithologists have come up with several theories about how the birds are able to do so.  Some ornithologists believe birds learn through visual observation during flight and use memorization to
identify features on the ground that they
can subsequently be refered to for orientation. In similar way, birds can use its other senses too. The location of the Sun and star patterns in the sky might also be used as an orientation mechanism in combination with other orientation information.  Birds can use the geomagnetic field of earth for their orientation as well just as us humans use compass. Certain features of Earth’s surface like
wind through mountain passes or waves
pounding a shoreline produce site specific infrasound signatures that could be used for orientation purposes by those species able to detect them. Smell can also be an important means of navigation. Different places on Earth have their own characteristic smell which can be used by the birds for detection of that site.
One way or another another, these birds are able to find their way back home and end what they had started. They keep on turning and completing this amazing wheel of life.