The most common and most likely answer to this crossword clue is the 6 plus 4 plus 5 letter word SPREAD ONES WINGS
I've seen this crossword clue in The Daily Telegraph
S
P
R
E
A
D
O
N
E
S
W
I
N
G
S
More clues leading to the result SPREAD ONES WINGS
Buddy explains!
The straight part
We know that "Act as a proud bird might/find new things to do" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case act as a proud bird might/find new things to do = spread ones wings.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.