Stymphalian birds

A flock of man-eating birds
they infested the woods
creatures of myth yes but
they were real enough
talking about them Stymphalian birds

Hercules drove them away, he rid the region
of these voracious birds
he clashed the krotala (a kind of clapper or
        castanet used in religious dances
        by groups in ancient Greece)
Athena was credited with an assist

They saw off the bloodthirsty birds
so numerous they destroyed the crops
they were carnivorous too
they lived in a swamp in Στυμφαλία
         in present-day, a closed karst basin
         located in the north-eastern
         part of the Peloponnese
also, most monstrous

Their feathers were sharp, metallic
    - are you sure about that?
they could be thrown like arrows
     - yes it is a matter of record 

Their beaks were bronze
    - no word of a lie
their dung was poisonous
    - you'd better believe it

They were the size of a crane
they became confused in cork
migrated to a marsh in Arcadia
destroyed the fruit trees
and tormented the townsfolk
talking about them Stymphalian birds