Having gone back & actually read the full lyrics (OK - I should have done that to start with) - this song seems like its about times when a group of men (male voices) are singing together at work and relaxing throughout the rural. I can't see any reason why this should be considered sexist. The meaning of the song would change substantially if you uni-sex-ise it. I don't think the changed version would be as strong and evocative - but that doesn't mean that you shouldn't be allowed to sing it that way....don't think there would be much point though. The sex of the observer is not specified - so its not as if there's that reason to change it in order for a woman to sing it.

Kris