Fascinating and ancient like man, the attitude to migrations is still today of a remarkable species of animals. At the head of the row are the birds, which demonstrate a mysterious ability to navigate and orient that scientists still cannot fully explain.
An instinctive tendency as ancient as the world and like the seasons, migration is an entirely animal attitude that is well suited to the world of birds, although it has not rarely been associated with human communities. The basic logic is always the same: we move from place x to place y due to climate change and food shortages.
When we talk about birds, however, in addition to these really important elements, we cannot even forget the wonderful and precise instinct that moves them, helping them in navigation and above all in orientation.
In order to have additional data on these innate abilities of all birds, numerous scientific studies and ornithological research have been conducted, which thanks to the observation and ringing of the species under study, are giving really interesting answers.
In principle, it can be said that the migrations of birds, which began in prehistoric times, when there was no lack of seasonal alternations, are probably caused mainly by the length of the days and therefore by photoperiodism.
When, to be clear, the hours of daylight are reduced there is also a biological regression of the development of particular glands of the birds which determine their aggressiveness and intolerance and which therefore allow the aggregation into groups necessary for departure.
The same conditions should stimulate the return journey and the abandonment of the wintering places, directed towards the nesting places.
If the outward journey is commonly called post-nuptial or pass, the return journey is rather known as a review and pre-nuptial flight.
Generally speaking, when we talk about migrations by birds, we can refer to a diurnal or nocturnal migration.
Very fascinating studies on diurnal migration were carried out in the early fifties by Gustav Kramer, who, placing birds subject to seasonal migration, inside large cages, noticed that they attempted to move, during the migratory period, with reference to the sun.
During the cloudy days, however, the birds moved chaotically, without a precise direction.
By altering the position of the sun, with a game of mirrors, Kramer could see that the birds followed the direction of the sun, albeit tampered with.
Studies made it clear that, while not observing the sun directly, birds subject to diurnal migration rely on the direction of sunlight to provide correct flight information.
Obviously in natural conditions the flocks will be able to rely not only on the sun, but on references of various kinds: first of all those of a topographical nature.
Kramer found out more! Birds are equipped with a “clock” and biological rhythm that guides them, 24 hours long that is well connected to the solar rotation and of course to the photo periodicity.
Unfortunately, still today we do not have a precise and confirmed idea of how birds are able to use this solar compass, which they now undoubtedly possess.
It remains to be discovered how and why some species are able to move easily with fog or perhaps clouds. According to some, acoustic navigation would come into play in this case.
Another type of migration is the so-called nocturnal one, moreover the one most practiced by birds which, even if they are active during the day, prefer the night to "travel".
Although there are few scientific studies that explain nocturnal migration, there is certainly no shortage of theories and experiments.
For example, it is assumed that many birds prefer to store energy during the day, through food, and fly for an entire night.
According to other theories, exactly how the sun would influence diurnal migrants, the moon would have the same role with the nocturnal one, yet the theory was very soon discredited by Drost and Kramer.
Griffin, however, in the late sixties demonstrated during his experimentation, that mallards, American garganeys, pintails and Canadian geese immediately found the right path only during nights with a clear, cloudless moon. On the other hand, situations of disorientation and panic could be encountered in the case of liberating nocturnal birds in cloudy nights. Yet the doubt remains: do nocturnal migrants use the moon or the stars to orient themselves?
Nor is there any explanation for the ability of nocturnal migrants to fly through thick clouds and fog without losing direction. Help could come to them from the noises they hear during the journey, but these are still unproven theories.
What seems clear is that several components come into play during migration. First of all that instinctive, since migration is innate, hereditary, and common to all animals. Migration is also familiar as young people usually migrate in the company of adults and experts.
Furthermore, migration occurs by imitation and thanks to memory and experience.
Younger groups learn family movements by imitation, relying also and above all, in case of need, on the hereditary component. Memory is also a very important factor for the orientation ability of migratory birds. It seems that they are able to mentally record environmental characteristics and local noises, which help them not to lose their way. Suffice it to say that the sound of a rifle shot causes an increase in flight altitude or even a change in the route.