Studies led by the Doñana Biological Station – CSIC, the University of Seville, the University Miguel Hernández of Elche with the collaboration of the University of Lisbon warn of the negative consequences coming with the use of landfills and intensive livestock farms as food resources by Eurasian griffon vultures (Gyps fulvus). The research work, carried out in the Ebro Valley, has been published in two scientific journals, Bird Conservation International and Avian Conservation and Ecology.

This work began as a result of the changes in the legislative framework that took place in 2014 and allowed farmers to abandon carcasses in the field instead of incinerating them. The aim was to compare the information obtained before and after this new regulation. Thanks to the information provided by GPS devices and accelerometers placed on 35 adult griffon vultures, the researchers identified 3,500 different places where the birds had found food. After visiting them, they detected that these places had many carrion resources and used to be associated with large rubbish dumps, intensive livestock farms (generally pig farms), and also landfills.

Ainara Cortés Avizanda, a researcher at the Doñana Biological Station – CSIC and scientific director of these research works along with José Antonio Donázar, highlights that "the most worrying thing is that only 9% of the feeding places we reviewed had an administration authorization that allowed to abandon livestock carcasses". This, according to the researcher, raises serious concern about the potential damage it can cause to the health of the birds since these food resources are not sanitary controlled".

The team also investigated whether the response to these food resources varied between vultures of different ages (immatures and adults). They used a mixed approach based on citizen science (observations by photographers and naturalists) and data provided by systematized scientific observations. The results showed that, after the introduction of the new European health regulations, the proportion of immature individuals substantially increased throughout the study area and was particularly higher in landfills and places with much carrion.

"This could happen due to the fact that these places have highly predictable food resources. The immatures would also avoid to compete with adults, that go to other places where there are better quality resources", explains Lola Fernández, from the University Miguel Hernández of Elche and first author of the study. "This poses a great risk to the health of immature individuals since, despite the fact that the food is guaranteed, they have a high probability of contracting diseases, becoming intoxicated or malnourished, all due to the lower quality of food".

The current regulations, not enough

As a whole, the results showed that the griffon vultures, the main providers of ecosystem services of all scavenger birds, exclusively depend on resources that could entail risks, either due to their nature (intensive livestock farms and landfills) or because they are usually located in highly humanized areas with higher risk of accidents for birds.

Furthermore, the effects may not be homogeneous within a population. There are regional administrations that have not yet modified their regulation according to the European health legislation, so extensive livestock farmers are not allowed yet to abandon the carcasses. In the regions in which the legislation already applies, farmers who have not yet used the new permits should be encouraged to do it. "Let the extensive livestock carcasses remain available for scavenger birds should be a priority. Sanitarian regulation that allow the abandon of carrion in the fields are insufficient, probably because they have not been applied with the same intensity, nor at the same time in all administrations", says José Antonio Donázar, one of the scientific directors of the studies. "This underlines the need to create policies beyond administrative borders".

On the other hand, according to the researcher, administrations should avoid that the remains of intensive livestock farms are left available for scavenger birds. They should also review the role of landfills, where many birds gather and where accidents and intoxications are common. "These food resources are a double-edged sword", Donázar explains. "They are extremely attractive for scavenger birds, but they can have very negative effects that go unnoticed".

According to the research team, it is necessary to obtain long-term information that allows to study populations as a dynamic effect to address the conservation of these long-lived species. This would also help to ensure the preservation of the ecosystem services provided by scavenger birds, a group that may be seriously threatened by the loss of extensive livestock farming and the homogenization of human and landscape uses in rural environments in the future.

Researchers from different organizations have collaborated in these studies: University of Seville (Ainara Cortés Avizanda), University Miguel Hernández of Elche (Lola Fernández Gómez, Eneko Arrondo Floristán), Doñana Biological Station - CSIC (Fiach Byrne, José Antonio Donázar, Marina García Alfonso) and the University of Lisbon (Patricia Tiago). The studies have been funded by the Community of Barcenas Reales in Navarra.

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Reference:

Lola Fernández-Gómez, Ainara Cortés-Avizanda, Patricia Tiago, Fiach Byrne, José Antonio Donázar. Food subsidies shape age structure in a top avian scavenger. Avian Conservation Ecology. https://doi.org/10.5751/ACE-02104-170123

Lola Fernández-Gómez, Ainara Cortés-Avizanda, Eneko Arrondo, Marina García-Alfonso, Olga Ceballos, Eugenio Montelío, José Antonio Donázar. Vultures feeding on the dark side: current sanitary regulations may not be enough. Bird Conservation International (2022). https://doi.org/10.1017/S0959270921000575