Larger birds displacing half the swallows (4)
I believe the answer is:
owls
'larger birds' is the definition.
'owls' can be an answer for 'birds' (owl is a kind of bird). I am not certain of the 'larger' bit.
'displacing half the swallows' is the wordplay.
'displacing' indicates an anagram (I've seen 'displaced' mean this).
'half the' means to take half the letters.
'swallows' with half the letters taken is 'lows'.
'lows' anagrammed gives 'OWLS'.
Can you help me to learn more?
(Other definitions for owls that I've seen before include "Slow sort of birds" , "Members of Parliament" , "Avian symbols of wisdom" , "Slow kind of birds" , "Slow (anag) -- birds of prey" .)