What typically influences why northern populations of Eurasian Eagle-Owls tend to be larger than southern ones?

Answer

Colder, northern regions yielding larger birds

Generally, birds in colder, northern regions tend to be larger than their southern counterparts, a principle often related to Bergmann's rule where larger bodies retain heat better.

What typically influences why northern populations of Eurasian Eagle-Owls tend to be larger than southern ones?
birdsizeowlEurasian Eagle-owl