Short swim for each bird (6)
I believe the answer is:
dipper
'bird' is the definition.
(dipper is a kind of bird)
'short swim for each' is the wordplay.
'short swim' becomes 'dip' (I've seen this in another clue).
'for each' becomes 'per' (per person).
'dip'+'per'='DIPPER'
(Other definitions for dipper that I've seen before include "Scoop" , "Ladle; bird" , "Diving bird" , "one browses selectively" , "Water bird - Great Bear" .)