Endless energy seen by seabird on the wing without end (7)
I believe the answer is:
eternal
'without end' is the definition.
(I've seen this before)
'endless energy seen by seabird on the wing' is the wordplay.
I cannot really see how this works, but
'energy' could be 'e' (physics symbol as in E=mc2) and 'e' is located in the answer.
'seabird' could be 'ern' (I've seen this in another clue) and 'ern' is present in the answer.
'the' could be 't' (the is pronounced as a 't' sound in some dialects) and 't' is present in the answer.
'wing' could be 'l' and 'l' is found in the answer.
A single letter 'a' remains which might be clued in a way I don't see.
This explanation may well be incorrect...
Can you help me to learn more?
(Other definitions for eternal that I've seen before include "like Rome?" , "Never-ending, existing always" , "going on for ever" , "Timeless" , "One being forever" .)