Madrigals are polyphonic. A madrigal is polyphonic. Madrigals are popular. A madrigal is popular. One other reason why the Indefinite Generic a tiger is ungrammatical with the predicate become extinct is that extinction can only happen to a species, and it means that every member of the species is dead.
Any tiger is in danger of becoming extinct.
That is, becoming extinct isn't something that happens to individual tigers.