Birds phonetically suggested by a feature of 17-, 27- and 51-Across

TOUCANS

Think of colorful birds whose names sound like a repeated "two" in the answers to those clues.

The clue hints at birds that sound like a feature shared by the answers to 17-, 27-, and 51-Across. The word "toucans" sounds like "two cans," suggesting that each of those three answers contains the word "can" twice. For example, if those answers were "candle," "canyon," and "cantina," each has "can" appearing twice phonetically, leading to the playful answer "toucans."