This is a video of a cinereous harrier.
Translated from Dutch daily Leidsch Dagblad:
On the day before Christmas, a worker at this museum in Leiden discovered that. The cinereous harrier (Circus cinereus) has already been in the Naturalis collection for nearly 150 years. However, so far it had not been linked to the British naturalist Charles Darwin, founder of evolutionism. ,,A special find”, a museum spokeswoman says.
See also here.
Bird evolution: here.