The story
Apparently first attested in English in 1839, in the writings of Darwin, and usually said to be from a native name imitating the bird's cry. However, compare dialectal Spanish carrancha (“dog collar with spikes”) (from *carrancula), a form of carlanca (metathesized from *carcannula, from Late Latin carcannum): the birds' coloration does sometimes resemble a collar.
Etymology from Wiktionary, CC BY-SA 4.0.