MLA

Howe, Susan, 1937-. Purple Heron.. 61 (Broadside). 1971-1972. https://collections.library.yale.edu/catalog/10171152.

APA, 6th edition

Howe, Susan, 1937-. (["61 (Broadside)"])(1971-1972)[Purple Heron.]. https://collections.library.yale.edu/catalog/10171152.