I found a somewhat longer quote in the book, "Michael Collins: A Biography," by Tim Pat Coogan, page 13, found by Google Book Search. The only source given is "Mary Collins Powell quotes a ballad of the time, 'which, no doubt, left a lasting impression on Michael's young mind.' "

Great faith I have in moral force
Great trust in thought and pen
I know the value of discourse
To sway the minds of men
But why should words my frenzy whet
Unless we are to strike
Our despot lords who fear no threat
But reverence the pike
Oh, do be wise, leave moral force
The strength of thought and pen
And all the value of discourse
To lily-livered men.
But if you covet not to die
Of hunger in a dyke
If life we prize is liberty
A Pike – A Pike – A Pike.