The immense bird of many North American nations whose wings are thunder and whose eyes are lightning.
Documented
On poles and stone
Thunderbirds crown totem poles of the Northwest Coast and mark petroglyphs across the continent, documented by ethnographers from Boas onward. Nations from the Pacific to the Plains hold related traditions.
Assessment: Documented in art, ceremony, and ethnographic record across hundreds of communities.
Stories
The mechanics of a storm
The stories give the weather an anatomy: wingbeats crack the thunder, the blink of its eyes is the lightning, and its enemies are the horned underwater serpents. Storms are battles in a war older than people.
Assessment: A complete explanatory system in folklore form. As meteorology it fails; as meaning it has outlasted empires.
Interesting claims
A memory of the giant teratorns
The claim: Thunderbird preserves an Ice Age memory of teratorns, condor-like birds with wingspans past five meters that overlapped with the first peoples of the Americas.
Assessment: The birds were real and the overlap was real. Whether memory survives eleven thousand years intact is exactly the question this archive cannot answer, which is what makes it a good one.
Sources and further reading
Boas, Tsimshian Mythology (1916)
Bureau of American Ethnology reports, petroglyph records
Plains and Northwest Coast ceremonial documentation
Teratorn fossil record, for the chronological claim
Worth asking
If the storm is an animal, what does that make the weather forecast?