Bird migration has been a theme that has at all times fascinated human beings, because the daybreak of time. The look and disappearance of assorted species, relying on the season, has fuelled numerous theories. According to Aristotle, on the finish of summer season the swallows landed on the reeds and magically reworked into frogs.
Incredibly, this speculation remained legitimate till the 18th century. Others, nonetheless, noticing the seasonal disappearance linked to the chilly of winter, believed that they have been getting ready for hibernation. For some peoples, birds have been able to migrating into house, reaching the moon and different planets.
Today, because of more and more exact applied sciences and research, now we have managed to grasp what the phenomenon of migration actually is, debunking the weird theories of the previous.
What can we learn about migration?
Let’s make it clear immediately, migration will not be a easy long-distance motion, however a exact and common phenomenon that repeats seasonally. Migratory birds are actual commuters, transferring cyclically between two areas, the breeding areas, to the north, and the wintering areas, additional south. In spring they head north to nest, in autumn they transfer south to spend the winter in locations with hotter and extra welcoming climates. It happens often yearly, with outlined outward and return migratory flows.
Generally talking, migrations are an adaptive response to seasonal modifications that affect the availability of assets. Birds are compelled emigrate, as they transfer from areas that change into inhospitable to them, with out meals and assets, to different areas that enable them to extra doubtless survive regardless of the risks of the journey.
Among the over 10 thousand recognized chook species, roughly 40% are thought of common migrants, and are current in virtually all orders and households.
In actuality, migration will not be a static and immutable phenomenon over time, it could actually change rather a lot in response to environmental modifications each between species and inside totally different populations of the identical species, and varies from area to area. Almost over 60% of the birds that breed in Northern Europe are migratory.
These excessive percentages are clearly linked to the robust seasonality of those areas. Based on how far the birds journey, they’re divided into two giant classes: full migrants, these during which all of the people of that species migrate, equivalent to swallows (Hirundo rustica) or bee-eaters (Merops apiaster), and partial migrants, these birds during which some populations migrate and others are sedentary, as occurs with blackbirds (Turdus merula) and robins (Erithacus rubecula).
When does migration begin?
Birds migrate primarily based on seasonal modifications, so migrations usually happen in autumn and spring. However, the instances inside these seasons can change enormously from species to species, and rely upon quite a few components equivalent to the gap from the wintering locations, the velocity of motion, the path to be taken, local weather modifications and the availability of meals. Those who need to journey an extended distance are additionally those who take the longest, so most long-distance migrants are among the many first to go away and likewise the final to reach
Those who spend the winter past the Sahara desert, for instance, just like the orioles (Oriolus oriolus) or the hoopoes (Upupa epops), often depart the nesting areas as early as the tip of summer season, between August and September, after which reappears in our woods in late spring, between April and June. Short migrants such because the black redstart (Phoenicurus ochruros) and the robin, nonetheless, migrate later.
They have much less floor to cowl and often have a tendency to go away in autumn, after which be the primary to reappear within the nesting neighbourhoods between the tip of winter and the start of spring. Let’s say that all birds know precisely when it’s time to depart. The variation within the alternation of hours of sunshine or darkness all through the day is usually the important alarm bell. When the second of departure arrives, migrants enter a state of migratory restlessness known as zugunruhe.
When the migratory frenzy will increase, a bit like what occurs to us once we realise that we do not have our luggage prepared two hours earlier than departure, the birds enter a state of agitation, written of their genes, which pushes them to arrange for the journey . In this part the birds begin to eat an increasing number of, to build up fats which is able to assist them face the migration in the very best means.
Where do migrating birds go?
Most migratory birds transfer alongside a North-South course. When winter arrives in Europe, most species transfer in the direction of sub-Saharan Africa, however there are a lot of others that may additionally transfer from East to West, usually in the direction of the Middle East. There are species that make shorter actions, transferring from upstream to the plain. In these instances we speak about vertical migrations, and contain for instance all these species that dwell within the excessive mountains and are available right down to the valley, equivalent to robins and redstarts.
Thanks to applied sciences and the ringing method, at this time we’re lastly beginning to perceive the place precisely the migrants go. Bird ringing for scientific functions is a examine method that entails the seize and individual marking of birds by a hoop utilized to the leg on which a singular alphanumeric code is imprinted, a bit like a automobile license plate.
Thanks to this, at this time we all know that almost all of European swallows winter in a really small space of Nigeria known as Ebbaken, the place many birds with European rings have been recaptured. Or that many migrants use the small islands within the sea as resting locations throughout their lengthy journeys. These small strips of land in the midst of the ocean are actual service stations the place you’ll be able to relaxation, recharge your batteries and set off once more.
Many of those islands are situated proper round Italy. But really distinctive discoveries have been made utilizing GPS information. For instance, GPS has helped us perceive that many migrants observe the coastlines and exploit the Straits, such because the Bosphorus, the Strait of Messina and that of Gibraltar, to maneuver, shortening the time and risking lower than a direct crossing above the ocean.
