The science. Why birds don’t (almost) migrate anymore

Shortening the distance travelled, returning early or simply stopping migration, climate change affects migratory birds on several levels. And this phenomenon is visible from our windows. “There are several hundred white storks in the Charente-Maritime that no longer migrate to Africa because the swamps no longer freeze in winter. Finally, they stay all year round near the breeding grounds,” says Jeremy Dupuis of the Bird Protection League (LPO).

The Charente-Maritime has a population of white storks that no longer migrate to Africa because the swamps no longer freeze over in winter. Jeremy Dupuis of the Bird Protection League

In addition to this sedentary trend, birds that are still migratory return early in the season: “Sub-Saharan migratory species winter hard in the north. On the other hand, they advance the date of their return in order to “stick” to the return of spring, which corresponds to the breaking of leaves and the explosion of insects, ”explains an expert from the association of ornithologists and naturalists. As for those whose wintering zone border is in France, they are sometimes not even observed in France. “In France, some waterfowl, such as ducks, waders or even herons, no longer winter with us. They have shortened the migration distance and they no longer have to travel to Western Europe during the cold season,” he explains.

Darwinian consequences

Are these changes in migratory routes worrisome? According to the LPO expert, this is not so. On the contrary, they demonstrate the ability of birds to adapt to climate change. Nevertheless, the climate hazard with the increase of extreme meteorological events can be fatal. Species that continue to winter south of the Sahara, such as swallows and cuckoos, may die from drought. For people who return early to Europe, beware of annual fluctuations, if the winter is harsh, they may die of cold or starvation.

But the trend towards an early return is not only a consequence of climate change. This behavior already exists outside of temperature rise. Why ? To be the first to arrive at the spawning grounds and enjoy the food. “With climate change, this ability to return earlier and earlier will be selected,” says Jeremy Dupuy. In other words, global warming is playing on natural selection, favoring birds that already tend to return early.

In addition to rising temperatures, migrants are under pressure during the three phases of their cycle – breeding and nesting, migration and wintering. “Bird habitats are being destroyed in breeding and wintering areas. As for the stops needed to replenish fat stores during migration, they often occur in wetlands, which are also at risk, ”specifies Jeremy Dupuy, emphasizing that this explains the complexity of migrant retention programs.

When the birds are no longer where you expect them

Be careful, the count can be misleading. Explanations by Jeremy Dupuis of the LPO: “In the 1990s, there were between 3,000 and 4,000 goldeneyes in France. Today there are less than 100.” Why worry, right? “No, because you need to look at European indicators, which are quite stable. These birds simply no longer come to France to winter, which corresponds to the southern limit of their wintering. »

Icon nameSnow partridge thrown to the height

Climate change affects migration as well as habitat and food resources. Also, rising temperatures have consequences for birds that do not migrate, in particular in France for specialized species in mountain pastures, meadows located at an altitude of more than 2000 meters above sea level. In fact, the forest tends to rise in height. However, the snow partridge, or rock partridge, which cannot adapt to the forest environment, is now forced to climb to higher altitudes to find its open environment with meadows and rock landslides. Fortunately for the gallinaceae, the presence of herds associated with still-existing pastoralism makes it possible to limit the expansion of the forest.

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