Gulls - birds eating whatever's left (5)

'gulls' is the definition.
The answer and definition can be both people as well as being plural nouns.
Maybe they are linked in a way I don't understand?

'birds eating whatever's left' is the wordplay.
'birds' becomes 'tits' (tit is a kind of bird).
'eating' indicates putting letters inside.
'whatever's left' becomes 'w' (I can't explain this - if you can you should give a lot more credence to this answer).
'tits' going around 'w' is 'TWITS'.

Can you help me to learn more?