I don’t know how you think of this story, and I don’t know how long you’ve worked at it, so please take everything I’m about to say as being like a fellow writer/editor in a writers’ group workshop. Whatever suggestions I might make (and that’s all they are, suggestions), this is in quite good shape and shows a lot of good thought behind it.
I think you’ve struck a good balance between conveying a different time period through linguistic constraint without making this early tribe sound stupid. I didn’t like ‘sibs’, either, especially as you had already used ‘brothers and sisters’ about a page earlier, but that’s a detail that may have struck you in a later draft.
Another nit-pick detail - first page, sixth paragraph - I’d suggest leaving the sentence at ‘despite his great youth.’ Your story’s narrative doesn’t seem to cover much more than a year, whereas saying ‘his great youth at that time.’ (italics mine) leads me to expect that you are about to tell the story of much more of his life.
I think the most important thing is to stress that Gerg’s ‘heightened’ style of singing is very different from the ‘everyday’ style of singing that is common in the tribe. The line about ‘our singing led to our talking’ is a little misleading - I was expecting something like Wales, where singing is a massive part of the culture and they take great pride in the quality of their music, and their ability to sing anywhere, anytime at the drop of a hat. Perhaps you meant that this tribe speaks a pitch language like Mandarin; if so, I’ve no idea how to describe that in the linguistic constraint you have chosen.
I’m curious about the evolution of his ritual - he sings to the sun once on the first day of no frost, and this develops into singing three times a day during a period in which no one is speaking about his singing. ‘Why?’ is an interesting question that doesn’t get answered. It’s cool - all prophets had to have a first day when they presented their ideas, and the first day of no frost seems like as good a day to thank the sun as any.
Is it really necessary for Mana and Gerg to have practiced? Totally fine if your answer is ‘yes’; I’m just thinking that it would have been challenging for them to sing without being heard by the others, it would have meant that Gerg was doing what was, to him at least, a sacred ritual out of context. Whereas the idea of someone spontaneously joining in seems more interesting to me.
How radical was the choice of the narrator as new Elder? I didn’t get a sense of the narrator being very old, and in fact, being banished for a time for the remark about Erona’s singing, along with the unthinking nature of the remark itself, made me think that the narrator was only slightly older than Gerg.
I don’t know why, specifically, but I had a strong sense that the narrator was a woman. I cannot put my finger on what gave me that sense.
Just some quick, random thoughts after a couple of readings. This is really good work, it makes me curious about what else you have written, and it makes me hope that you will join in some of the SDMB Short Fiction contests in the future.