White Faced Owl

A White Faced Owl in a private collection. But is it a Northern or a Southern White Faced Owl? What are the distinguishing features that make it one or the other?

Thanks.

The eye-colour will usually tell Northern and Southern apart:
Northern = eyes vary from deep amber-yellow to orange
Southern = eyes are red

So the one in the photo is a Northern then?

Thank you very much Mike - that's really useful information.

The Northern White-faced Owl is generally paler than the Southern, but the other main difference (besides eye-colour) is in their vocalizations: the call of the Southern is described as "a series of fast, bubbling hoots". The Northern has a very different, two-note call.
(Which is of zero help when identifying birds from photographs )