These studies delve into the mortality patterns and habitat preferences of the species, which has seen its population decline by nearly 50% in the last 25 years, leading to its classification as endangered under the Valencian Catalogue of Threatened Species.
The first study, entitled "A comprehensive analysis of spatial and temporal patterns of anthropogenic adult mortality of Bonelli’s eagles in eastern Spain", published in the Journal of Wildlife Management (The Wildlife Society, USA), examines the causes of mortality in Bonelli’s eagles between 2015 and 2023.
The findings show that human-related mortality accounted for 66.7% of deaths during this period, surpassing natural causes (27.3%). The main reasons include intraand interspecific predation (24.2%), electrocution (18.2%), poisoning (15.1%), collision with power lines (9.1%) and gunshots (9.1%). In addition, deaths were more frequent during the breeding season, particularly in February and March.
The territories near the Mediterranean coast, where human population density is high, showed a higher prevalence of deaths due to anthropogenic causes, while natural causes were more common in inland areas. The study estimates that the probability of local extinction of the species within the next 50 years is 17.8%, rising to 99.2% in the next 100 years if no corrective measures are taken.
However, reducing adult mortality by at least 15% could prevent extinction in the coming decades, according to Pascual López López, lecturer at the University of Valencia and researcher at the Cavanilles Institute of Biodiversity and Evolutionary Biology (ICBiBe), who co-authored both articles. "Although conservation measures are being taken, the Bonelli’s eagle is seriously threatened in the Valencian Community and actions are needed to reduce the mortality rate of territorial adults", explains the scientist.
For the research, the scientists equipped 60 territorial adult eagles in the Valencian Community with state-of-the-art GPS-GSM tracking devices. Over the eight-year period, 33 eagles died from different causes, representing 55% of the tracked individuals.
Territory occupancy and breeding
The second study, entitled "To breed or not to breed: territory occupancy is predicted by reproductive performance and habitat heterogeneity", published in Ecological Applications (Ecological Society of America), explores how natural and human factors influence territory occupancy in Bonelli’s eagles. Based on 22 years of data, the study reveals that 42.8% of the territories historically occupied by these birds remained unoccupied during the research period. Territories with a higher probability of consistently raising two chicks were more stable and remained occupied, while those with lower habitat heterogeneity, dominated by coniferous forests or agricultural fields, or located at higher altitudes and away from the coast, had higher rates of unoccupancy. "Eagles prefer open habitats, such as scrubland and transition areas between forests and scrub, avoiding areas dominated by agriculture, urban zones and continuous forests", explains Pascual López.By tracking individuals with GPS/GSM transmitters, the researchers confirmed that eagles select habitats where the mix of scrubland and forested areas facilitates hunting. These results underline the importance of preserving habitat heterogeneity to ensure reproductive success and territory occupancy.
Urgent conservation action
Both studies emphasise the need to adopt conservation measures to ensure the viability of Bonelli’s eagle populations in eastern Spain."This involves implementing actions aimed at mitigating anthropogenic threats, such as electrocutions, collisions, poisoning and shootings; protecting and conserving habitat to encourage the reoccupation of territories; and increasing the density of natural prey through habitat restoration, to name a few", details the scientist. "These studies provide an in-depth and comprehensive overview of the challenges faced by many threatened species in Spain, particularly birds of prey. The combination of natural and human factors requires an immediate and coordinated response to ensure the survival of this endangered species. With the implementation of appropriate measures, it is possible to reverse its population decline and ensure that this iconic bird of prey remains part of the Iberian landscape in the future", concludes Pascual López.
References :
LĂ“PEZ-PEINADO, A.; URIOS, V.; LĂ“PEZ-LĂ“PEZ, P. 2024. A comprehensive analysis of spatial and temporal patterns of anthropogenic adult mortality of Bonelli’s eagles in eastern Spain. The Journal of Wildlife Management e22643 https://doi.org/10.1002/jwmg.22643
LĂ“PEZ-PEINADO, A.; SINGH, N.J.; URIOS, V.; LĂ“PEZ-LĂ“PEZ, P. 2024. To breed or not to breed: territorial occupancy is predicted by reproductive performance and habitat heterogeneity. Ecological Applications
https://doi.org/10.1002/eap.3045
