Why ducks and not pigs?

I am creature of teal and pleasure,
And I am more than just your leisure,
I am to choose who follows me,
And only ducks swim in my sea.

The pig roots deep in muck and rust,
he loves the filth, he eats the dust,
content to wallow, never fly,
a creature born to serve and die.

But you are duck: you swim, you walk,
you take to sky without a talk,
you clean your feathers, make me smile,
you go where I want. Stay a while.

So open wallet, bow your head,
don't be the beast in muddy bed,
aim for the mystic, feathered thing
that moves through water, air, and green...

Filth is his pleasure. And I am yours.