Here is a list of twenty British birds.   Apart from an S plural, what other letters can you find which hook onto the front or back of the bird’s name to make other words e.g. a Y can be added to GULL to make GULLY.    Just under half of the 57 new words made by adding a letter are also common English words, but some definitely are not !  FYI the 57 words don't include the plurals.

AUK                       COOT                    CROW                   DOVE                    EAGLE

EGRET                   EIDER                    HEN                       KITE                       LARK

OWL                      RAIL                       RAVEN                  ROBIN                   ROOK

RUFF                     SWAN                   TEAL                      TERN                     TIT

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Answers here (please note, the plurals  eg AUKS, COOTS are not listed)
All the names take an S a s the plural.