When you picture a magnificent flying bird, it is usually not a chicken that comes to mind. I've never seen a chicken portrayed in flight-many eagles, but no chickens. We quote the Scripture from Isaiah 40:31 that talks about being borne up on the wings of eagles or with wings like eagles. There is a difference, however, between being on His wings and being under His wings.
This promise in Psalm 91 is not elaborating on the flying wing but on the sheltering wing. One indicates strength and accomplishment, while the other denotes protection and familiarity. When you imagine the warmth of a nest and the security of being under the wings of the nurturing love of a mother hen with chicks, it paints a vivid picture of the sheltering wing of God's protection that the psalmist refers to in this passage.