A format supported by an increasing number of music programmes is Music XML (See List).
I believe Sibelius imports it, but needs an expensive plug-in before it will export the format directly.
There is, however a work-around. PDFtoMusic does a good attempt at converting the PDF scores output by Sibelius into Music XML. It is a commercial programme, as is it's big brother PDFtoMusic Pro. The free demo versions are limited to converting the first page of a score, but a single folk tune doesn't even need a full page, so no problem there.
The conversion I tried as a test had a couple of obvious errors, but wouldn't need much tweaking or correcting.
Quack!
Geoff the Duck.
p.s. are those maggots nice big fat juicy ones? ;¬)