here's what I came up with:

Once I had a duck and I named him "Earl"
I later found out that Earl was a girl
But it didn't seem to matter to the duck at all
'Cause Earl would always come to me whenever I would call

I gave my duck a shelter from the wind and rain
He slept in my barn and ate up all my grain
You may say that ducks are simple and they have no sense at all
But Earl would always come to me whenever I would call

Well Earl was feeling lonely so I got another duck
I thought it would be nice to name her "Lady Luck"
But as it turned out Lady Luck was a boy
Which made Earl the girl simply "Quack!" for joy

Chorus

Very soon I realized that they would like to be alone awhile
So I left them with a wink, and a knowing smile
But Lady Luck, he turned cold and just didn't feel right
Screaming "E-a-r-l!" in the passions of the night

Well, they came up with a fix, though I thought it rather strange
It was that each of them (you guessed it) should have a sex change
Seems they didn't realize, and I guess that I just didn't say
That they only had to switch their names to save the day

Well, brushing all this aside, they settled down to raise their family
And I decided not to name the ducklings too hastily
I used to think that all the ducks – they were the same
But now I wonder which comes first – the duck, or the name?

And why do all the ducks come in disguise
When some of them are girls, and some of them are guys?