The establishment of 3 territories in the study area after 11 years of releases can be considered a success according to the criteria of the IUCN/SSC (2013), especially considering that the maximum number recorded in the 90s for the Bonelli's eagle in the region was 5–7 pairs (Torrea et al. 2021). However, this positive result is also due to the rest of the actions carried out within the life projects, such as the correction of power lines, improvements in the habitat or the awareness of the hunters in Navarra, which have allowed the released birds to survive and reach to settle in the area.
The first year survival of the released individuals (54.38%) is within the values described for the species in different wild populations of the Iberian Peninsula (Real & Mañosa 1997; Arroyo et al. 1998; Balbontín et al. 2003; Soutullo et al. 2008) and southern France (Hernández-Matias et al. 2011), with a minimum survival of 36% (Arroyo et al. 1998) and a maximum of 69% (Balbontin et al. 2003), and is very similar to that recorded in previous works with the species on the island of Mallorca with specimens from captive breeding (53.33% Badia-Boher et al. 2021).
Regarding the causes of death detected, our work coincides with previous studies carried out in the Iberian Peninsula in that the majority of deaths are due to causes of anthropic origin, mainly electrocution (Real et al., 2001; Rollan et al. 2016, Grefa, 2020). However, our results show percentages of birds electrocuted, poisoned or shot to death that are much lower than those described in these studies. This difference is due to the great importance that predation acquires in our area, reaching 44% of casualties, while, for example, in the work of Real et al (2001) it did not reach 0.5%. The increased role of predation is due, in our opinion, not only to an increase experienced by the Golden Eagle (Aquila chrysaetos) (Del Moral, 2009) and the Eagle Owl (Bubo bubo) (Escandell and Escudero, 2020) main predators identified, but above all to a decrease in deaths from human causes. Throughout these 11 years, agreements have been signed with the main electricity companies present in Navarra to guarantee that electric pole designs with low risk of electrocution are used in the new lines and that the existing ones are progressively corrected in accordance with guidelines and courses implemented (Grefa, 2020) and a subsidy line has been created for the correction of power lines of small owners (Gobierno de Navarra, 2022). Because of these actions, several thousand kilometers of power lines have been corrected, making the electrocution rate in Navarra 50 times lower than that found in the south of the Peninsula (GREFA, 2020). However, the large movements that this species makes throughout the Iberian Peninsula (Real and Mañosa, 1997; Cadahia et al. 2009) and even the south of France (Hernandez-Matías et al. 2010) means that these correction measures lines are insufficient if they are not applied throughout the country or even at European level.
When correcting the causes that led to its disappearance at the end of the 90s, those of natural origin that were hidden by the high number of electrocutions, poisonings or deaths by gunshots that occurred in those years appear. After this unexpected result, it is necessary to reassess the capacity of current habitats to house the Bonelli's eagle, taking into account the current abundance of both its prey (Carrascal and Seoane, 2009; Caro et al. 2011; Real et al. al., 2016; Martínez-Miranzo et al. 2019), as well as their competitors and even predators (Carrete et al. 2006; López-López, 2011; Gil Sánchez, 2018). Our work shows that it is possible to recover historical territories of Bonelli's eagle through the release of birds with hacking techniques, but also that many highly interrelated factors intervene in the management of the species and that require a continuous review of the criteria. The development of long-term monitoring with radio-tagged specimens will allow obtaining the necessary information to direct the management of the species.