The superpowers of migratory birds revealed by science

You admired the performances of the athletes at the Paris Olympic and Paralympic Games ? You can marvel at even more incredible feats by looking up and watching migrating birds fly through the clouds. When the sports media are amazed at the record – not approved – established in 2019 by the marathon runner Eliud Kipchoge, which fell below the two-hour mark, the tiny Anadyr sandpiper, which does not exceed 30 cm and 250 g, covers several a non-stop flight the equivalent of 126 marathons during its annual migration between Australia and Korea.

Such exploits, The world on the wingby Scott Weidensaul, is full of them. In his book – finally translated into French – this American amateur ornithologist and journalist specializing in environmental issues since the 1970s paints a global panorama of migrants and their wonders, but also of the threats that the human species poses to them, risks seeing these champions of the air disappear.

« Golden Age of Ornithology »

We know these wonders better and better thanks to two technological revolutions that have occurred over the last thirty years: the miniaturization of sensors on board birds – barely a gram for some – and geolocation. With fifty years of experience, the author does not hesitate to speak of a « golden age of ornithology »as these new devices, coupled with networks of ground radars, make it possible to push the limits of knowledge on migratory birds.

For a long time, ornithology was also content with« a blinkered vision » and limited itself to the study of the European and North American breeding grounds of migrants, without knowing where these feathered beings went when winter came.

From now on, we measure ever more incredible distances and routes, like the Arctic tern, champion of all categories, which travels approximately 80,000 km during its annual migration from one pole to the other, some pushing up to 92,000 km. A new object of study for ornithology thus appears: migratory connectivity, i.e. the geographical connection of individuals or populations between the different stages of the annual cycle.

« We realized how much we had underestimated the immensity of the physical capabilities of migratory birds »

In addition to the breathtaking distances covered by migrants, this approach highlights the extraordinary physiological capacities that allow them to accomplish such flights. To fly at an altitude of 7,200 m and cross the Himalayas, bar-headed geese have developed a respiratory system capable of renewing the air at such high altitudes. To prepare for their seven to nine day non-stop flight between Alaska and New Zealand, the Godwits accumulate up to seventeen times more fat in their metabolism, which they burn more efficiently. than humans without risk of dehydration.

Unable to throw ballast, some birds become lighter by shrinking their digestive and reproductive organs during the flight, or even by cannibalizing their internal tissues, without long-term damage.

Discovery of new vulnerabilities

Finally, we now know that many migrants use, to orient themselves in the night, nothing less than quantum entanglement which allows two photons to be intertwined, whatever their distance, with one striking the eye. of the bird and the other remaining in the stars by means of which it navigates. In short, « Over the past two decades, we have realized how much we have underestimated the immensity of physical capabilities » migratory birds, observes the ornithologist.

« These are creatures whose full life cycle must be understood »

If migratory connectivity makes these champions of the air even more admirable, it in contrast reveals their fragilities, increased by the damage perpetrated by the human species throughout the planet. Because, as Scott Weidensaul says: « Migratory birds are not residents of a given place, but inhabitants of the whole ; These are creatures whose full life cycle must be understood if we are to have any chance of preserving them against the assaults they endure at every moment and at every stage of their migratory journey. »

What happens in winter affects the entire migration: this is called carryover effects, « which could be decisive for the long-term survival of hundreds of migratory species ».

This is the sad observation made by Californian ornithologists in the 1990s, observing in just a few years the collapse of Swainson's hawks in the Butte Valley, where the raptors were protected. Knowing that the buzzards spent the winter in Argentina, the scientists went there and discovered with horror the transformation of the pastures where the birds were accustomed to living into monocultures of sunflower and soya copiously sprayed with pesticides. The Argentine government's ban on the pesticide quickly reversed the trend and restored the Swainson's Hawk population.

Among the first victims of climate change

Ces « carryover effects » can be seen in both directions: in Western Europe, the population of black flycatchers is collapsing dramatically. With an ever-increasing delay of a few days, these migrants leaving from the West African forests miss the peak abundance of insects on which their juveniles feed. Insufficiently nourished, few newborns reach adulthood.

When they are not directly targeted by human activities, migratory birds, sentinels of nature, are among the first victims of climate change. Many wintering areas risk ending up underwater within a few years. This is the case in the Bahamas, where the islands on which the rare Kirtland's warbler nests — already saved from a first extinction in XX^e century thanks to a federal policy of habitat restoration — do not exceed a few meters in altitude.

Glimmers of hope

Moreover, The world on the wing contains some glimmers of hope. On the one hand, it shows that with political will, we can prevent the decline of migrants. As urbanization and the proliferation of dams ravaged the Yellow Sea, one of the wetlands most frequented by millions of migrants, located between China and Korea, the Chinese government banned development in the mid-2010s. coastal. The positive effects were immediately felt on the avian populations.

In Nagaland, in northeast India, the inhabitants of Pangti agreed in just a few years to put an end to the massive culling of hundreds of thousands of Amur falcons, sources of significant income in this region. Very poor state, where individuals killed or captured were resold. Supported by the federal government and ONG international, they proclaimed their village “ capital of falcons », hoping to turn their former prey into a tourist attraction… and a sustainable source of income.

In the United States, hummingbirds from Alaska have been observed spending the winter in Pennsylvania rather than in the Amazon jungle for some time. Previously, these few stray individuals were stuck there and died in these cold lands without having reproduced, but things are changing now that the winter climate has become milder. These birds, which should have died a few decades ago, now find themselves in the position of pioneers capable of « to transmit [leurs] once-deleterious genes to new generations ».

Such developments, while still marginal, are not happening fast enough for all migrants. If we still wish to contemplate these great and small champions of the skies in the future, the main lever remains within ourselves and in our way of inhabiting and sharing the Earth.