Bats -- small fliers (7)

I believe the answer is:

cuckoos

'fliers' is the definition.
(cuckoo is a kind of bird)

'bats small' is the wordplay.
'bats' becomes 'cuckoo' (both can mean mad).
'small' becomes 's' (abbreviation - e.g. clothes size).
'cuckoo'+'s'='CUCKOOS'

(Another definition for cuckoos that I've seen is " They lay eggs in other birds' nests".)

I've seen this clue in The Telegraph.

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