By Yoav Perlman
An Imperial Eagle was found in Holland on September 27th. It was on show for a short while and then went missing, to the disappointment of quite many twitchers. On October 3rd it was relocated and showed much better. From the start there was debate whether it is a Spanish or an Eastern. At this age, fourth-plumage, both species are not easy to separate. Björn Malmhagen (remember him from Stejneger’s Stonechats?) posted in a Facebook discussion this beautiful annotated photo-composite demonstrating why it is an Eastern Imperial Eagle (Aquila heliaca) rather than Spanish (A. adalberti). I thought it is worth publishing here.
Björn based his knowledge on proper research he did with Hans Larsson. They studied field photos, and also spent time at NHM Tring studying skins there. They published a great article in the Swedish magazine Vår Fågelvärld in 2012. Here is a taster:
Many thanks to Björn and Hans for sharing this exciting material. Björn asked me to thank Mark Adams of NHM Tring for allowing access to the materials for their study.