Thanks to more than three decades of monitoring, researchers at the University of Granada reveal how human absence during the pandemic impacted the reproduction of a threatened species: the Bonelli’s eagle

Scientists at the University of Granada (UGR) have revealed the real impact of human activities on endangered wildlife, taking advantage of the ‘natural experiment’ provided by the COVID lockdown. The research has been published in the journal Biological Conservation.

Using data from more than 1,200 reproductions of Bonelli’s eagles (Aquila fasciata), the authors found that their reproduction improved substantially in 2020. That year, the average number of chicks born per pair was the highest recorded in the 31 years of monitoring.

According to José María Gil and Marcos Moleón, scientists from the Department of Zoology at the UGR who led this work, «the lockdown coincided with critical stages of reproduction: the end of the incubation period and the entire time the chicks were growing in the nest. The absence of disturbance by humans in the vicinity of the nesting sites resulted in exceptional reproduction for our times, but reflects what must have been normal before human pressure reached current levels.»

The research reveals that the human factor poses a much greater threat to reproduction than natural elements, and that the activities that have the most negative impact are decoy partridge hunting and traffic: “The former carries a high risk of mortality from shooting of breeding eagles and chicks from lead poisoning, while the latter is related to other secondary activities such as hiking and mountain biking.”

More than three decades of monitoring and a lockdown

“Revealing the real impact of human presence on wildlife is complex, as under normal conditions there is no reference point without human activity with which to compare the extent of other possible natural constraints, such as weather conditions, competition with other species, or prey abundance,” the authors note. In this study, data from three periods were used: pre-COVID (1994-2019), COVID (2020), and post-COVID (2021-2024).

When it comes to endangered species, methods based on experiments are often impractical or directly involve an ethical conflict, so alternative techniques must be used. This analysis is based on the continuous monitoring of the breeding population of Bonelli’s eagles in the province of Granada, which the authors began in the early 1990s.

“Since then, year after year, we have visited all occupied and potential territories to estimate basic parameters, such as the percentage of pairs that successfully raise chicks and the number of chicks that survive,” says José María Gil Sánchez.

The work is innovative. There are hardly any scientific evaluations that take advantage of the COVID lockdown to examine the human impact on wildlife, especially on endangered species and outside urban environments, probably due to the lack of long-term fieldwork and the difficulties of going out to sample during those days.

“In our case,” the authors explain, “monitoring was possible thanks to a special permit issued by the UGR to go into the field, and to the work carried out during the de-escalation by all members of the research team in the province of Granada, in their respective municipalities.”

Caring for the Bonelli’s eagle

The results describe the main measures to be implemented to ensure the conservation of the Bonelli’s eagle in southeastern Iberia. First, the prohibition of decoy hunting for partridges, a practice that is culturally ingrained in areas of southern Spain, “but which is illegal under European law,” the study’s authors emphasize.

Secondly, the regulation and control of access by hikers, visitors, cyclists, and climbers in the vicinity of nesting sites, especially during the eagles’ breeding season, approximately from December to May.

“In the absence of this study, it was difficult to identify the most efficient management actions. Now that they have been identified, it is time to prioritize them and put them into practice, something that is not only the responsibility of environmental managers, but also of society as a whole, so that we can all make responsible use of our natural environment,” the authors conclude.