What does the cryptic crossword clue "Diving bird endlessly showing signs of breathlessness (6)" mean?

The definition is "Diving bird". The wordplay uses a deletion. PUFFIN (deletion) = PUFFIN; definition: "Diving bird" The answer is PUFFIN.

Diving bird endlessly showing signs of breathlessness (6)

Times Cryptic #28657 | 1 Across | 2023-07-17 flower