Things to know about bird migration
It clatters and creaks. It sounds like a tractor rolling up. Far and wide we can’t see one. After a time of disorientation a view into the sky provides an explanation:
Thousands of cranes fly over the chain of hills in the middle of Germany, in the neighborhood of Wetzlar. The cranes crank up into the heights from their resting areas in the riverside systems. Soon, after some chaos in the beginning, they build their typical V-formation in the sky.
The strong, experienced birds fly at the top in the middle and form the first offshoots of the V in the front. After them at the sides the families with their on average two young stocks follow.
The formation is the secret how each individual bird with reduced effort overcomes the distance from the middle of Europe, Scandinavia or the Baltic countries towards the south.
At an average of 80 kilometers per hour the cranes could make it from the middle of Germany to Southern Europe without a stop. Nevertheless, they sometimes take a pause, sometimes fog or bad weather forces them to stay on the ground for days.
The bird of luck as one of the tallest birds of migration
More than one hundred thousand cranes stay in France, while the majority travels to Spain, mainly to the light oak forests at Extremadura. Just a few thousand birds move to Portugal or Northern Africa. Cranes are resident on five continents and even in Europe, and in size with just one single species of the Common Crane (Grus grus) it is significantly taller than the Gray Heron or the White Stork. The Common Crane makes it up to the size of a school child with its 120-130 cm.
While the tallest species of cranes, the Sarus Crane (Grus antigone) in South East Asia and Northern Australia reaches the size of a grown-up with 170 centimeters. As omnivores cranes harvest rests of vegetables or cereal grains on the fields during their way southwards.
However, for their brood and the breeding of the young stock they need wet habitats. These are decreasing on a global scale and endanger single populations.
The rather tall bird of migration was regarded as particularly alert and clever in the Greek mythology, it was named the bird of luck. Also in China cranes were considered as wise, they promised a long life when seeing them.
From hibernation to a flight to the moon
Cranes are only one, although a very tall and fast migrating bird species. From all globally roughly 10,000 bird species more than half migrate in winter. The way and distance differs depending on the species.
Short-distance migrants like cranes, lapwings, fieldfares, meadow pipits or skylarks take their way on search for food in winter only to warmer parts of Western Europe or the Mediterranean regions. They adapt to weather conditions, stay longer in breading areas in a warm fall or come back earlier in mild winters.
Whereas nightingales, white storks, cuckoos, red-backed shrikes or swifts as long-distance migrants always start their migration at the same time of the year. They fly towards areas south of the Sahara, the Garden Warbler even travels from the center of Europe to Southern Africa for the winter. Arctic Terns travel half of the circumference of the earth, when flying 25,000 kilometers into its wintering grounds and back. In its life the Arctic Tern collects in average one million kilometers. Sandpipers manage 10,000 kilometers without a pause, but even small birds reach non-stop-flights of up to 3,000 kilometers. It makes them survive when they have to cross the sea and deserts.
Aristoteles was one of the first to observe the bird migration in a scientific way.
However, he lacked a sufficient data base and explanations. He interpreted the disappearance of migrating birds with them going into hibernation. Less scientific oriented observers strongly believed that the birds migrated to the moon in winter. The first realistic assessment why and where birds disappeared happened by Friedrich II. of Hohenstaufen in the 13th century. On the first congress for ornithologists 1884 in Vienna the participants finally decided to observe the migration of birds in a systematic way. Following the model of astronomical observatories they established the first bird observatory in Rossitten, East Prussia, in the year 1901. There researchers introduced bird ringing then.
The genes determine
A study in North America on the Swainson’s Thrush revealed that the genetic specification for the way and the time of bird migration of each species is determined in a relatively small group of about 60 genes.
The Swainson’s Thrush divides into two subspecies: the one occupies the Canadian east coast in summer and migrates west to Mexico and South America, whereas the other subspecies flies from Canada’s interior via the southeast of the US into the south.
Hybrids of both subspecies take a dangerous route in the middle of both flight paths across mountains and deserts. With this the hybrids have only marginal chances of survival. Thanks to them though the researchers could identify the genetic anchoring of the migration birds’ behavior.
Within three to six generations migratory birds adapt their behavior to environmental changes. They are strongly affected by climate change and the ongoing land consumption. As migratory birds they are dependent on intact habitats in their breeding areas, at resting places as well as on food supply at their wintering areas.
According to a study of BirdLife International only 13% of the species profit of the climate change, many deal with big risks for surviving. Among the endangered species one third fight for their survival in consequence of the changing climate. The British nature conservation organization RSPB found that birds like the nightingale will have to overcome enormous distances without nutrition on their flight way because of the growing deserts. To find the right migration route birds orient themselves on the sun, the stars and mainly on the magnetic field of the earth. Researchers at the university in Oldenburg found molecules called crypthochromes let birds perceive the magnetic field as visual pattern in their retina.
For managing the flight in the best way birds prefer to migrate in social associations not only with the own species.
Dr. Wulf Gatter has observed the migration at the Swabian Alb for decades, supported by ZEISS. According to his observations birds get together depending on their individual speed and their daily pattern of migrating. Birds may adapt to the group. One example he shows are bramblings, where males may have nearly double the weight of female Common Chaffinches. Still bramblings fly with chaffinches and head the group, although they are slower than if they travel only with their own species.
The community of travelers saves energy for each individual bird this way and they are better protected from raptors. Sören Rust finds outside of Hamburg, at the Carl Zeiss’ bird station in the marshland of Wedel, the best conditions to observe birds in social associations or pure groups of one species. The member of the young birders’ club tested his new digiscoping equipment at bird migration in October and describes us his experiences.
Fall in the marshlands
After late summer this year continued with summerly temperature and lots of sun until well into October, fall really came on now. In bird life the last weeks around Carl Zeiss’ bird station in the marshlands were characterized by a change of shifts among the birds. The breeding birds collected and migrated southwards, while numerous migratory birds used the nutritious Wadden area of the river Elbe to rest. Also the first winter guests slowly arrive. First the swallows and the Yellow Wagtails left the marshlands.
During September they gathered around the Carl Zeiss’ bird station to cross the Elbe together at the smallest area close to the marina. On some days we could view thousands of swallows in the mornings or evenings from the station as they spent the night at the water there. In mid-September the birds of prey migration reached its peak. In minute intervals marsh harriers, ospreys, honey buzzards and sparrow hawks crossed the marshlands.
My personal highlight has been two Pallid Harriers, who flew over the station within two hours on their way to the south. Those were my first sights of Pallid Harriers and at the same time only the fifth and sixth evidence of this species for Hamburg. In the beginning of October bird migration gained rather late momentum despite the summerly temperature. In the marshlands of Wedel the first barnacle geese showed up and more than 300 snipes rested at high tide close to the station.
I have never seen so many snipes before in the area. During low tide they searched for food in the Wadden area together with lapwings and Eurasian Golden Plovers. At high tide they paused at the islands of our bird station and I could perfectly film and photograph them with my ZEISS Conquest Gavia spotting scope and the adapter for digiscoping. While on water resting ducks and waders dominated, the sky was full of cranes and Greater White-Fronted Geese on their way west.
On the water close to the clay tapping point, there is at the moment another spectacle to observe when hundreds of cormorants collectively hunt fish.
The collaborative hunting helps to drive the fish into the bay at the shore, so they are easier to capture for the cormorants. The wintering great white egrets have learned this and just wait for the hunt of the cormorants to get the fish served at the shore. Often you see dozens of herons lining up at the waterfront who wait.
Excitement comes into bird life when suddenly a sea eagle approaches and lands on one of the islands directly in front of the observation hide. In this moment you first realize how tall a sea eagle really is, when it directly sits in front of you and not only circles in the sky.