The most common and most likely answer to this crossword clue is the 5 plus 7 letter word HOUSE SPARROW
I've seen this crossword clue in The Sunday Telegraph
H
O
U
S
E
S
P
A
R
R
O
W
Buddy explains!
The straight part
We know that "is one chirpy?" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case is one chirpy? = house sparrow.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.