Deathless seabird observed in wild lea (7)
I believe the answer is:
eternal
'deathless' is the definition.
(thesaurus)
'seabird observed in wild lea' is the wordplay.
'seabird' becomes 'tern' (tern is a kind of seabird).
'observed in' indicates putting letters inside.
'wild' indicates anagramming the letters.
'lea' is an anagram of 'eal'.
'tern' put within 'eal' is 'ETERNAL'.
(Other definitions for eternal that I've seen before include "Never-ending, existing always" , "Undying" , "Perpetual" , "Ceaseless" , "Not stopping" .)