In Native American mythology, a bird-like supernatural spirit. It was believed to cause thunder when it beat its wings and flash lightning from its eyes. The thunderbird was also said to have the ability to remove its bird skin and assume human form. Web resource here.

‘Namgis artist (of the Kwakwaka’wakw). Thunderbird Transformation Mask. 19th century. Alert Bay, Vancouver Island, British Columbia, Canada. Cedar, pigment, leather, nails, metal plate. Brooklyn Museum.