Proof that Once She Was a Mermaid

[Magpie]

This is good, not a lot to say as regards critique for me, I've left a couple of notes below

Proof that once she was a mermaid --- I do like the title as it sets the premise of accusation, however the poem for me doesn't offer any 'proof' as such.

She denies it with a laugh -
shakes her head and disagrees -
but dips a taste of sourwood honey --- nice word choice with 'dips', 
and doesn't fear the bees.

Her warm green eyes swim --- 'warm green' not working for me
with memories of the seas  --- I like the first stanza and the rhymes up to this line, but then the rest of the poem doesn't have any rhymes. Is this intentional? It seemed odd 
and when a siren calls -
some ambulance from hidden streets --- would a 'police' siren work better considering the accusatory tone
of dreary londontown -   --- London town?
she doesn't harbor  --- good word choice
secret fears that it's for her
just shakes her head in sympathy for me.

She loves the taste of animals that hoof
the earth and graze the fields so openly -
who would not pretend to love
the taste of fish or salad greens?

But I won't sow the earth with seeds of salt 
or hide my eyes and ears to free my dreams.
No, bind me to this mast and let me hear her song
as others cry with emptiness -
the king's men starving at a feast.

Lots of good word choices throughout. Really enjoyed reading