Humans have often contemplated the remarkable ‘sixth sense’ of birds- a sense that allows them to migrate annually to warmer climates in search of replenished resources and mates, without any verbal communication or GPS devices. The question we so incessantly pose remains: how do they do it?
Although we recognise that birds have prerequisites to migrating such as indulging in nourishment for optimising energy expenditure, only a few scientific theories tend to currently explain their matchless behaviour. We have had numerous ideas as to how, why, when and where birds migrate. Today, we have modernised theories that are quite dissimilar to initial propositions, for example the one in which Aristotle claims that birds morph into different animals during the winter season. Instead, English scientist Charles Morton argued that birds journey to the moon, vacationing there until summer struck their homes on Earth. Essentially, when knowledge on bird migration was a modicum, theories such as these seemed fitting; after all, it’s thrilling to envision a petite European Bluebird transforming into a Siberian Tiger.
Charles Morton argued that birds journey to the moon, vacationing there until summer struck their homes on Earth!
Fortunately, modern technology has allowed scientists to stray away from primitive beliefs towards more cogent conclusions based on genuine migration data. Tools such as geolocator loggers and Passive Integrated Transponder (PIT) tags are used to monitor bird movements over space and time, although this still proves to be difficult. Based on statistics gathered by these apparatuses, there are several principle philosophies that explain the sixth sense as we know it today.
Flocking behaviour is often seen in birds. Source: pexels
Unquestionably, the most mesmerising theory reasons that a combination of cryptochromes and iron rich crystals in birds’ eyes enables them to see earth’s magnetic fields, a phenomenon known as magnetoreception. Within these magnetic fields, electrons belonging to free radicals evade bonding to generate a disruption of energy. Existing as blue-green light receptors, the cryptochromes detect such energy inequalities and help pilot birds by affecting their reactiveness to light; effectively, these exclusive morphologies design a visible map of the world below. To validate this assertion, an experiment was conducted by placing a magnetic device nearby a cage in order to alter the direction of earth’s actual magnetic field and craft a false sense of direction. When released, the captive birds flew out from the cage in the manipulated direction, supporting the concept of magnetoreception.
Additionally, birds use landmarks and particular topographies as check and resting points for their relocations. It is fundamental to plan where and when one must stopover on an arduous journey; unfortunately, as they voyage one of the thirteen global flyways, birds are finding it more difficult to recognise landmarks due to the ever-changing geography of the planet. Anthropogenic impacts such as the construction of sky scrapers and the destruction of natural habitats has greatly increased the risk of migration in the past century. A 2014 article in Condor states that annual construction-related bird deaths vary from 360 million to 990 million in the United States- a devastating statistic. Moreover, habitat degradation critically reduces the amount of available rest space, sending the perplexed birds into panic as they are forced to search for another safe site or compete with another species for resources.
Geese flying in a V-formation. Source: pixabay
As if all of this wasn’t shocking enough, it’s time to consider how certain migration aerodynamics exhibit superior travel tactics; the famed flying V formation has contributed to the game plan of hockey teams and the flying of airplanes, but was initially inspired by bird movements. This setup allows the leading bird to generate a series of downwash movements, consequently producing upwash by which the trailing bird can catch a free lift off the rising air. They stay in model formation through being able to sense the vortex created by this recurring motion. This clever strategy allows birds such as the Canadian Goose to lessen drag, and has been estimated to be 71% effective in flying proficiency.
Although scientists have gathered measurements to help support modern migration theories, a restlessness to understand precisely how bird migration occurs still persists; nonetheless, we’ve certainly deviated from thinking birds vacation on the moon, and with the advantage of contemporary technology we can continue exploring the fascinating flight of our feathery friends.
