Just come across this thread from looking for alternative lyrics to go with the tune - I was always told the lyrics below related to the English civil war (not sure they are authentic) but that the tune is originally 16thC. with different lyrics which I am trying to track down!

Here is how I learnt it -

Ah Poor bird
Take thy flight
Far above the sorrows of this dark night

When all men
Keep their own
Strive they not to put themselves upon the throne

This King now
He hath placed
In the hall of Jesus Christ his own slim face

Brother 'gainst brother
Fathers, sons fight
How are we to stem the wounds by reason's might?

Ah Poor bird
Take thy flight
Far above the sorrows of this dark night