Air bhioran - literally on a stick. In Norwegian we have an expression saying that you "står på pinne for ..." - are standing on a stick for someone. But in that case it means that you are on your toes, eager to help and please the one that you are "standing on a stick for." I'm wondering if that expression could have the same roots?
What you are heading is the R sound, which comes out sounding to English speakers more like RD. This happens because Gaidhlig uses a rolled R. In English when you pronounce an R the tongue isn't used, so it will likely be hovering in the middle of the mouth or pulled back out of the way. In Gaidhlig for every R sound the tongue will touch the roof of the mouth or the back of the upper teeth (varied by dialect or individual).
It's easy for English speakers to think of a rolled R as something that only happens when the R is extended, but it also happens with quick Rs too. This explains most of the odd sounding effects around Rs. For example, the S sound that manifests in the word ceart is actually a whistle effect that comes from moving the tongue from the top of the mouth to between the teeth