A team of Spanish and Portuguese scientists led by the UGR has unraveled the ancestral history of one of the most iconic birds of prey in the current Iberian fauna: the Bonelli’s eagle (Aquila fasciata).
The study, published in the scientific journal People and naturecombines evidence from several disciplines, including paleontology, genetics and ecology, to answer questions about when and why Bonelli’s eagle, a species found mainly in tropical and subtropical regions, colonized the Mediterranean region.
As Marcos Moleón Paiz, senior lecturer at the UGR Department of Zoology and lead author of the paper, explains: “The Bonelli’s eagle is a ‘newcomer’ in Europe. This species probably began to establish itself in the Mediterranean region in no more than 50,000 individuals. years ago, while others, such as the golden eagle (Aquila chrysaetos), have been here much longer, as evidenced by the fossil record.”
The spatial analysis conducted in the study showed that cold climate periods are largely unfavorable for the Bonelli’s eagle, but not for the golden eagle. “During the last ice age, the Bonelli’s eagle could only find refuge in warm coastal areas, and that is exactly where the oldest fossils of this species have been found,” says Moleón. Genetic analysis confirmed that around the Last Glacial Maximum the Mediterranean population of Bonelli’s eagles consisted of only a few individuals. This ancestral population of Bonelli’s eagles flourished as temperatures rose in the Mediterranean and the human population grew and became sedentary.
But as Moleón notes, “Once the question of ‘when’ was resolved, the inevitable question arose: why did the Bonelli’s eagle begin to colonize the Mediterranean during such a complex climatic period? And why did he settle during the last ice age? cycle and not before?”
The role of our ancestors
According to Moleón, “after testing several alternative hypotheses, all the pieces of the puzzle indicated that the first colonists of our species (Homo sapiens) in Europe played a fundamental role.”
The study collected and analyzed the most comprehensive information currently available on the competitive interactions between Bonelli’s eagles and golden eagles. This allowed the scientists to confirm that the golden eagle is the dominant species and the Bonelli’s eagle is the subordinate species in this relationship. Thus, the results showed that Bonelli’s eagles can only survive in places where golden eagles are rare, and that is mainly in areas densely populated by humans.
Moleón continues: “Moreover, our mathematical models showed that if we could eliminate all existing golden eagle pairs in climatically favorable areas, we would expect a significant increase in the number of Bonelli eagle pairs, but not the other way around. We also know that golden eagles can kill Bonelli’s eagles and take over their territories, but not the other way around.”
It is worth noting that golden eagles are less tolerant of human presence than Bonelli’s eagles. The authors hypothesize that with the arrival of the first anatomically modern humans in Europe, some of the golden eagle areas closest to human settlements were abandoned and that these “empty” areas were then occupied by Bonelli’s eagles from the Middle East. ‘In short, Bonelli’s eagles had not been able to establish themselves in the Mediterranean before the arrival of the first Homo sapiens because the competitive pressure from golden eagles and other species would have been too overwhelming,” the UGR researcher adds.
Living close to or far from people
Knowledge of the ability of humans to influence the distribution of species is nothing new. The novelty of this study lies in revealing a mechanism called ‘human-mediated competitive release’ through which our species, including our ancestors, could indirectly influence the distribution of other species, including long-lived species. “To understand what we observe in nature today, we often have to look to the past,” says Moleón.
However, the advantage that living close to humans once gave to Bonelli’s eagles has now turned against them. “Paradoxically, the future of the Bonelli’s eagle in the Mediterranean is currently threatened by the relentless intensification of human activities in the environment, which is reflected, among other things, in deaths caused by power lines, the lack of prey and the disruption of breeding sites ”, the authors conclude.
