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How Do Birds Navigate During Migration?

Dhanashree Patane
The sky is the limit? No it is not. The sky is limitless. So how do birds navigate their way during migration? GPS or what? This story brings to you all the navigational strategies used by birds to migrate.

Quick Learners?

Many birds are able to navigate back to their nests only in a few preliminary first flights!
Ever since the evolution of the Earth, there is one living species that has fascinated all by making the sky their home - birds. Blessed with sheer beauty and extraordinary flight skills, birds have raised the bar when it comes to tactics and smooth flying skills.
There is however one mystery that birds continue to keep alive; their ability and skills to navigate. Research and study has left no stone unturned to decode the strategies that birds use to navigate directions and routes. The simplest answer is that, they use visual cues like geographical features, mountains, rivers, etc., to navigate.
For directions, they follow the Sun. And? Well, contrary to the simplicity of this answer, birds actually have more complex, yet smart calculations that they use. Know exactly how they map their flights, reach for the southern skies with the onset of the winter chill, in the following.

Blue Bird Navigation Strategies That Birds Use to Migrate

The Magnetic Compass

➢ Many animals use the geomagnetic field for directional information. Navigational skills used by birds can be credited to the physiological compass that they possess. Researchers believe that birds use the magnetic field of the Earth to learn about directions, orientation, and navigation.
➢ Research hints at birds having a molecule called magnetite, which contains iron. This helps them orient according to the magnetic field of the Earth, similar to the way a compass needle indicates the magnetic north direction. Magnetite is believed to be present in abundance in a bird's beak. From here, the information is passed on to the brain through a branch of a nerves called the trigeminal nerves.
➢ Another possible mechanism, researchers suggest, is that birds have cryptochromes, or we could say 'specialized' molecules in the retina of their eye.
When light enters, these receptors cause a chemical reaction, and changes their chemistry, and the magnetism of the Earth can influence them. Birds possibly create images in the retina with these light-sensing cells, which enables them to navigate locations.
➢ Initially, a direct connection could not be proved, however, it is now found that these connections exist between a region responsible for vision in the brain of a bird, which is called 'Cluster-N', and the retinal cells that contain cryptochrome.

Making Mental Maps

➢ A complex system of spatial memory is found in birds. This memory can be described as the memory that stores places, and also the relationships between two places. Birds use this memory for orientation, thus creating mental maps. This is how they can remember routes, and also calculate distances and safest routes to reach a particular location.
➢ Birds also support their mental maps with the help of gradient maps. A gradient map has a minimum of two gradients of the landmarks which intersect at a specified angle. So, with the increase or decrease in gradient, birds will know the direction. They also compare their home gradient with current location, and are able to determine their way back home.

Sense of Smell

➢ A study conducted by researchers also found that birds used their olfactory senses (sense of smell) to navigate. Birds may follow the smell that wind brings along their route of navigation.

➢ An experiment proved this theory, where birds oriented to a certain smell. For example, that of food. Gradient maps that are created by foods and other smells could give birds some directional information.

Sense of Sound

➢ Some birds also use their hearing senses as cue to orientation. Birds can actually detect the sound of frequency that is below 10 Hz. The nocturnal call notes from rivers, frog calls, breaking surfs, and from flying, are some of the auditory cues that they use. They find the source of the sound by the frequencies of the detected signals.
➢ Inter-aural delay helps them define the direction of sound. Other factors, like the difference in phase, time arrival, and amplitude of sound, also helps them with the source of sound. Many migratory birds also use their sensory receptors to navigate and extract directional information from nature and the surroundings.

Sun Navigation

➢ Birds also use the position of the stars and the Sun to navigate. A bird may take cue from the position of the Sun to determine the time and its path. It is believed that the circadian rhythm of birds is tied to the Sun's compass.
➢ An experiment proved this theory. Starlings were kept in a cage that had opaque walls and a glass top. When the skies were clear and in good sunlight, the starlings oriented in the correct direction. However, under cloudy skies and low sunlight, the birds oriented randomly. So, it is the Sun that helps the birds orient, and hence, assist navigation.
➢ It is also believed that birds use polarized light, which is the light that occurs in an arc, 90 degrees from the position of the Sun. This light helps them navigate even in low light or cloudy conditions.

Star Navigation

While the Sun helps birds to navigate during the day and to migrate, there are some birds that migrate at night. So, they use the stars as cue to orientation.
The position of the stars, like constellations, are also helpful in orientation for some birds. In a study conducted, it was observed that birds changed their orientation when a star pattern was shifted. They not only use the North star, but also the pattern of constellations to navigate.
These were some of the navigational strategies that birds use. Much research has been a part of all the above findings by many researchers. The pattern that these birds have adapted and their navigational skills have evolved over the years. So, we could say that environmental cues and genetics have made navigation possible for birds.
Even with all the research, a concrete understanding of the 'sixth sense' that birds use for navigation, remains a mystery. We can only imagine the kind of math and calculation that takes place in the mind of a bird, the moment it spreads its wings for a flight!