How does the great gray owl appear so large?

The great gray owl (Strix nebulosa) appears exceptionally large, often reaching lengths of more than 70 cm (2.3 feet), primarily due to its plumage.3

This species is characterized by very full, fluffy feathers that provide significant insulation against the cold in its northern forest habitats. While the bird is indeed among the largest of the owls, much of its perceived size is an illusion created by this dense, loose feathering rather than its actual body mass.123