Great Grey Owl - Standing 27 in tall with a wingspan of 52 inches this is USA's longest owl (Strix Nebulosa). USA. When vole populations crash in the boreal forests where they nest they often move south in search of food. Photographed in northern Minnesota during one of the largest invasions on record in the winter of 2004/2005.They breed in North America, Alaska and from Scandinavia across northern Asia.