The most common and most likely answer to this crossword clue is the 8 letter word CHICKENS
I've seen this crossword clue in The Daily Telegraph
C
H
I
C
K
E
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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 = chickens.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 CHICKENS mean?
CHICKENS noun- A domestic fowl, Gallus gallus, especially when young.
- The meat from this bird eaten as food.
- The young of any bird; a chick.
- A coward.
- A young or inexperienced person.
- A young, attractive, slim man, usually having little body hair; compare chickenhawk.
- The game of dare.
- A simple dance in which the movements of a chicken are imitated.
- To avoid a situation one is afraid of.