The most common and most likely answer to this crossword clue is the 8 plus 3 plus 3 plus 5 letter word STRICTLY FOR THE BIRDS
I've seen this crossword clue in The Guardian
S
T
R
I
C
T
L
Y
F
O
R
T
H
E
B
I
R
D
S
Buddy explains!
The cryptic/wordplay part
In cryptic crossword there's often an wordplay/cryptic part as well.This part involves a more complex hint, such as an anagram, homophone, hidden word, etc.
Sadly, We don't have an explanation for this specific crossword clue yet.