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The Life of Valkyria: A Golden Eagle’s Journey
10. December 2024
Enrique Navarro, Daniel Gambra
THE AEQUILIBRIUM + PROJECT: Study of the mediterranean golden eagle (Aquila chrysaetos homeyeri) across its distribution range.
The multidisciplinary project “AEQUILIBRIUM” began to take shape in the summer of 2016, based on the principle of collaboration and understanding between two groups that, at least in Spain, have often appeared quite antagonistic in recent years: the “hunting community” and the “conservation community.” From this perspective, efforts and resources were combined to initiate this project as an example of how both worlds can indeed collaborate and generate scientific results.
In its initial phase (2017–2019), the entities TAGONIUS and ACE (Asociación del Corzo Español) jointly developed this project, focusing particularly on the impact of the roe deer (Capreolus capreolus), which is undergoing a significant expansion in central Iberian territories, on the breeding success of Mediterranean golden eagle pairs that share these geographic areas. Over these three years, we conducted several monitoring activities, including nests tracking and tagging of adult territorial individuals, across the provinces of Madrid, Soria, Burgos, Segovia, Cuenca, Toledo, and Guadalajara.
This first phase included the tagging of the adult female identified as “VALKYRIA” (marked with a PVC long-distance readable ring [81]) (Figure 1), the subject of this specific report. This female was first sighted during Christmas of 2010 in one of the breeding territories in southeastern Madrid province that TAGONIUS had been monitoring for years. She was a young female, in her second or third year based on her plumage (hatched in 2008) and was soon observed engaging in courtship flights with the resident male (named “BUCANERO”), who had lost his mate that same autumn. In spring 2011, “VALKYRIA” was observed incubating in a new nest on a small rocky ledge known as “Cueva del Cura” in Nuevo Baztán. However, she failed in her breeding attempt that year.
It was not until the 2012 breeding season that she successfully reared her first two golden eagle chicks as part of the new breeding pair (“BUCANERO”-“VALKYRIA”).
Years passed as we continued monitoring the progress of this breeding territory, coinciding with the birth of the “AEQUILIBRIUM” Project. After successfully raising two chicks in the 2016 season (both of which were ringed at their usual nest), “VALKYRIA” was selected as the first adult individual to be equipped with a GSM/GPS transmitter for the project. In early autumn, we started to attract VALKYRIA culminating on November 15, 2016, when she was captured using a wild boar (Sus scrofa) carcass as lure. Once captured, she was fitted with a 50 gr. e-obs transmitter (TAG-4991) and released at the capture site.
Since that day, “VALKYRIA” has provided continuous data on her territorial use, successfully breeding again in the year following her capture.
By the end of the 2019 season, and given the exceptional scientific results derived from nest tagging and prey monitoring through camera traps installed at the monitored nests, the project transitioned into a new phase called “AEQUILIBRIUM+.” This phase, developed and executed solely by the conservation association TAGONIUS, gained academic support from the Technical University of Madrid (Universidad Politécnica de Madrid), specifically through the School of Forestry, Environmental, and Natural Resource Engineering. This new phase, far more ambitious in terms of resources, geographic scope, and scientific objectives, is currently ongoing. One of the main objectives is monitoring of both territorial adults and young dispersing eagles (tagged in their nests as chicks), with GSM/GPS using e-obs devices as our primary equipment provider.
Eight years after her initial capture, “VALKYRIA” continues to provide invaluable scientific information on her territorial use. Over this time, she has changed consort males twice and has continued to successfully raise chicks almost every year in new nests.
One of the key findings from VALKYRIA’s data is the evolution of her home range over time. Using Kernel density estimation methodology to delineate her territory at the 95% and 50% levels, we observed notable changes since she was tagged in 2016 (Table 1). Specifically, the size of her home range has declined over the years, both for the overall territory (Kernel 95%) and the core area (Kernel 50%). The only exception occurred in 2020, when a reproductive failure resulted in a broader use of her territory.
Table 1. Area (in km2) of VALKYRIA’s home range using 95% and 50% Kernel using GPS data points for eight consecutive years.
| Year | Kernel 95% | Kernel 50% |
| 2017 | 166.63 | 26.07 |
| 2018 | 61.12 | 4.44 |
| 2019 | 77.74 | 7.33 |
| 2020 | 204.72 | 7.19 |
| 2021 | 68.37 | 3.42 |
| 2022 | 31.27 | 2.42 |
| 2023 | 24.62 | 1.67 |
| 2024 | 21.95 | 0.68 |
Valkyria_territory_2017-2024
Several factors may explain this decline in Valkyria’s home range. Firstly, a new pair of golden eagles established a territory adjacent to the western boundary of hers. The female of this pair, named “ÓPERA,” was also equipped with a GPS/GSM transmitter in 2020, specifically a 42 gr. e-obs tag. Since 2021, VALKYRIA’s movements appear restricted in the western region, likely due to competition from this neighbouring pair (Figure 2). Secondly, another new pair of eagles recently settled in the southern area of VALKYRIA’s territory, further constraining her range in that direction.
Additionally, future anthropogenic activities could force VALKYRIA to adjust her home range further. A solar farm is planned between the territories of VALKYRIA and ÓPERA, and this development is likely to impact the boundaries of both territories.
Our long-term objective is to equip both partners of these female golden eagles with e-obs GPS tags. This would enable us to study their interactions throughout the year and assess their behavioral responses to large-scale human developments, such as the photovoltaic farm.
Contact:
Organisation: TAGONIUS asociation, the AEQUILIBRIUM+ project.
Name: Enrique Navarro (Project director)
Phone: +34 667 612 100
E-mail: enrique.navarro@aequilibrium-project.org
Website: https://aequilibrium-project.org/
Social media (IG): https://www.instagram.com/proyecto_aequilibrium/?hl=es
contact@e-obs.de 
+49 (0)89-420016-0 
+49 (0)8153-887 2559 
