Observations on Short-toed Eagles nest in 1972
This is one more article from the Ardeola website:
• IRIBARRER, J.J. and RODRÍGUEZ-ARBELOA, A.., 1973 – Observaciones en un nido del Águila Culebrera (Circaetus gallicus), Navarra 1972 // Ardeola 19(1), 101-106. – 
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The text was published in 1973 including some black-and-white images. The placed PDF doesn’t have the best quality, but it’s fairly readable.