What does the cryptic crossword clue "Rocky boulder is revealing avian pest (9)" mean?

The definition is "avian pest". The wordplay uses an anagram. anagram of BOULDER + IS = BIRDLOUSE; definition: "avian pest" The answer is BIRDLOUSE.

Rocky boulder is revealing avian pest (9)

Independent Cryptic #11708 | 11 Across | 2024-04-19 flower