The most common and most likely answer to this crossword clue is the 7 letter word LINNETS
I've seen this crossword clue in The Daily Telegraph
L
I
N
N
E
T
S
Buddy explains!
The straight part
We know that "Birds" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case birds = linnets.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.
What does LINNETS mean?
LINNETS noun- A small passerine bird, the common linnet (Linaria cannabina, syn. Carduelis cannabina), in the finch family Fringillidae, native to Europe, western Asia, and north Africa.
- A house finch (Haemorhous mexicanus), of North America.