1955-1970 the maker’s mark was used with a copyright symbol. However, the Artist Series enamel brooches weren’t a thing until the 70s, so I would say this one is between 1970 and 1975.
Manufactured by Fallon and Kappel of New York.
Scuff on the head of the bird, otherwise in excellent condition.
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Eisenberg Enamel bird brooch, from the Artist’s Series