09/10/2021 at 6:21 PM CEST
A group of scientists from the Max Planck Institute for Animal Behavior and the University of Konstanz, in Germany, have identified some characteristics in the transoceanic flights of landbirds that allow them to travel enormous distances without stopping, in conditions that at first seem very complex.
According to a press release, the researchers used GPS tracking technologies to be able to appreciate in detail the itineraries that five species of large land birds follow, accustomed to carrying out long sea voyages. The research has been published recently in the journal Proceedings of the Royal Society B.
According to previous studies, birds make these trips taking advantage of the so-called “tailwind”, a horizontal wind current that blows in the direction of flight of the birds, allowing them to save energy. It is worth remembering that maintaining a flapping flight for hundreds of kilometers is an enormous effort and requires a high cost of energy, for large birds and a considerable weight.
If we go back further in time, over the course of several centuries, bird watchers thought that terrestrial species did not exceed a distance of 100 kilometers when flying over the sea, and that they did not directly face the dangers posed by the open oceans. Not only were they wrong, but science has also managed to demonstrate what mechanisms allow birds cross those abysmal distances in supposedly unfavorable contexts.
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The German study has examined the behavior of 65 birds of five different species when crossing the ocean, obtaining unpublished information on how they birds terrestrial they survive such long flights and do not even need to make stopovers to rest or forage.
How do they do it? Apparently, the key is in two variables: wind and elevation. The specialists conclude that the birds take advantage of the best atmospheric conditions to reduce energy costs during the flight, but that it is not a random matter: they select the routes according to these conditions and are even capable of modifying the itineraries to find the ones. ideal characteristics.
The specialists studied the routes for nine years, obtaining global atmospheric information that allowed them to identify the criteria used by birds to select their migration routes over the open sea. For example, they found that most species opt for time periods and flight zones that guarantee them favorable lifting conditions.
The birds optimize the wind support when selecting their sea crossing routes, while choosing higher elevation when adequate wind support is available. This means that “Smart routes” that birds follow are sustained by a combination of the two factors: wind and elevation.
The role of elevation
Why is the elevation? The favorable conditions of elevation allow that the crossing by sea is less demanding in terms of energy, by reducing the resistance. Although the impact of elevation was previously thought to be weak or absent on the sea surface, new research has shown that it plays an important role for birds.
On the other hand, the discoveries also confirm that many landbirds depend on atmospheric support to complete their migrations over the open sea, marking the vulnerability that they present in the face of any change in the Earth’s atmospheric circulation patterns.
The interplay of wind and uplift facilitates over-water flight in facultative soaring birds. Nourani et al. Proceedings of the Royal Society B (2021) .DOI: https: //doi.org/10.1098/rspb.2021.1603
Photo: an Eleonora’s hawk flying over the islet of Alegranza, in the Atlantic Ocean. Despite being powerful fliers, hawks are highly selective of supporting winds during transoceanic migration. Credit: Wouter Vansteelant.