Caress a seabird with a decorative design (7)
I believe the answer is:
pattern
'a decorative design' is the definition.
(I've seen this in another clue)
'caress a seabird' is the wordplay.
'caress' becomes 'pat' (patting is a kind of caressing).
'a seabird' becomes 'tern' (tern is a kind of seabird).
'pat'+'tern'='PATTERN'
'with' acts as a link.
(Other definitions for pattern that I've seen before include "Blueprint, design" , "Ornamentation" , "Stencil" , "Arrangement of decorative motifs" , "Sewing plan" .)