Stroke a seabird with a decorative design (7)
I believe the answer is:
pattern
'a decorative design' is the definition.
(I've seen this before)
'stroke a seabird' is the wordplay.
'stroke' becomes 'pat' (pat can mean to stroke or touch).
'a seabird' becomes 'tern' (tern is a kind of seabird).
'pat'+'tern'='PATTERN'
'with' is the link.
(Other definitions for pattern that I've seen before include "Stencil" , "Repeated decorative design" , "Sewing plan" , "Arrangement of repeated parts of design" , "Decorative design; model" .)