They resemble gulls wheeling around the stern (5)
I believe the answer is:
terns
'they resemble gulls wheeling' is the definition.
The definition suggests an adverb but the answer is not.
'around the stern' is the wordplay.
'around' indicates anagramming the letters.
'stern' anagrammed gives 'TERNS'.
Can you help me to learn more?
(Other definitions for terns that I've seen before include "Sea bird with long forked tail" , "Rents out these birds" , "Aquatic birds" , "Sea birds with long forked tails" , "Seabirds" .)