What unique facial structure does the Northern Harrier share with owls, hypothesized to aid in sound location?

Answer

Facial disc

The Northern Harrier possesses facial feathering that creates a facial disc, a feature rare among diurnal raptors but shared with owls, which is thought to help funnel sound to their ears.

What unique facial structure does the Northern Harrier share with owls, hypothesized to aid in sound location?
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