Why is a vulture that can fly 400km a day never crossing the border?

by christels

And feed on carrion vulture is a large bird of prey (raptors) s can fly more than 400km per day. It turns out that such vultures inhabit many in the eastern Spain on the Iberian peninsula in western Europe, but few in the neighboring west Portugal. A research paper summarizing why vultures do not fly to Portugal has been published.

Invisible barriers: Differential sanitary regulations constrain vulture movements across country borders-ScienceDirect
https://www.sciencedirect.com/science/article/abs/pii/S0006320717315550

Un muro invisible se alza entre los buitres de España y Portugal | Ciencia | EL PAÍS
https://elpais.com/elpais/2018/02/15/ciencia/1518707418_741915.html

There are many vultures in Spain. However, when Eneko Arrondo, an ecologist, attached GPS-mounted tags to 60 white- bellied vultures and 11 black vultures and observed their distribution, it was only in two years that he entered Portugal next to Spain. I found that all of them were back to Spain.

1 / A vulture can fly up to 400 kilometres each day in search of carrion.Little should it care whether this flight takes it from one country to another.The vultures of Spain, however, skirt around the Portuguese border with uncanny accuracy.pic . twitter.com/UE9kjuXWK5

— Bruno Martin ???? (@TurbanMinor) April 3, 2019

The border between Portugal and Spain is along rivers and canyons, and there is no significant difference in climate or topography between the two countries. However, in Spain there are many vultures, whereas in Portugal there are few vultures.

4 / The Portuguese-Spanish border follows river valleys and is not associated with abrupt changes in climate or land-use.What is different on either side, the team learned from Portuguese ornithologists, is the law.pic.twitter.com/8au6Do7CLm

— Bruno Martin ???? (@TurbanMinor) April 3, 2019

Arrondo argues that the treatment of dead cattle is related to the vast population difference between Spain and Portugal. The cow carcass is an important food for vultures whose main food is carcass. In Spain, it is customary to leave cattle carcass intact, but in Portugal it is mandatory by law to dispose of cattle carcasses by burying them or burning them.

In Europe, it was forbidden to leave livestock that died in 2001 due to mad cow disease . However, in Spain, fierce objections have emerged that collecting, transporting, and disposing of dead cattle is costly and that carbon dioxide emitted during incineration causes climate change. As a result, the abandonment of cattle was allowed again in Spain under certain conditions, such as being far away from the city.

In search of carcass to feed, large vulture colonies are distributed along the Spanish border, but due to the lack of carcass due to mad cow disease measures, the number of inhabitants tends to decrease year by year . Arrond commented, “The survey found that the mad cow disease measures taken in the EU had a negative impact on the natural environment.” BirdLife International, an organization that advocates nature conservation in Spain and Portugal, said, “Aligning sanitation policy across borders benefits wildlife.”