Doctors, popular with seabirds (7)
I believe the answer is:
interns
'doctors' is the definition.
(intern is a kind of doctor)
'popular with seabirds' is the wordplay.
'popular' becomes 'in' ('in' can mean trendy).
'with' is a charade indicator (letters next to each other).
'seabirds' becomes 'terns' (tern is a kind of seabird).
'in'+'terns'='INTERNS'
(Other definitions for interns that I've seen before include "Hospital residents" , "those confined" .)